ArticlePDF AvailableLiterature Review

Unhealthy Landscapes: Policy Recommendations on Land Use Change and Infectious Disease Emergence

Authors:

Abstract and Figures

Anthropogenic land use changes drive a range of infectious disease outbreaks and emergence events and modify the transmission of endemic infections. These drivers include agricultural encroachment, deforestation, road construction, dam building, irrigation, wetland modification, mining, the concentration or expansion of urban environments, coastal zone degradation, and other activities. These changes in turn cause a cascade of factors that exacerbate infectious disease emergence, such as forest fragmentation, disease introduction, pollution, poverty, and human migration. The Working Group on Land Use Change and Disease Emergence grew out of a special colloquium that convened international experts in infectious diseases, ecology, and environmental health to assess the current state of knowledge and to develop recommendations for addressing these environmental health challenges. The group established a systems model approach and priority lists of infectious diseases affected by ecologic degradation. Policy-relevant levels of the model include specific health risk factors, landscape or habitat change, and institutional (economic and behavioral) levels. The group recommended creating Centers of Excellence in Ecology and Health Research and Training, based at regional universities and/or research institutes with close links to the surrounding communities. The centers' objectives would be 3-fold: a) to provide information to local communities about the links between environmental change and public health; b) to facilitate fully interdisciplinary research from a variety of natural, social, and health sciences and train professionals who can conduct interdisciplinary research; and c) to engage in science-based communication and assessment for policy making toward sustainable health and ecosystems.
Content may be subject to copyright.
1092
VOLUME 112 | NUMBER 10 | July 2004
Environmental Health Perspectives
Human-induced land use changes are the
primary drivers of a range of infectious disease
outbreaks and emergence events and also modi-
fiers of the transmission of endemic infections
(Patz et al. 2000). These land use changes
include deforestation, road construction, agri-
cultural encroachment, dam building, irri-
gation, coastal zone degradation, wetland
modification, mining, the concentration or
expansion of urban environments, and other
activities. These changes in turn cause a cascade
of factors that exacerbate infectious disease
emergence, such as forest fragmentation,
pathogen introduction, pollution, poverty, and
human migration. These are important and
complex issues that are understood only for a
few diseases. For example, recent research has
shown that forest fragmentation, urban sprawl,
and biodiversity loss are linked to increased risk
for Lyme disease in the northeastern United
States (Schmidt and Ostfeld 2001). Expansion
and changes in agricultural practices are inti-
mately associated with the emergence of Nipah
virus in Malaysia (Chua et al. 1999; Lam and
Chua 2002), cryptosporidiosis in Europe and
North America, and a range of food-borne ill-
nesses globally (Rose et al. 2001). Road build-
ing is linked to the expansion of bushmeat
consumption that may have played a key role
in the early emergence of human immunodefi-
ciency virus types 1 and 2 (Wolfe et al. 2000),
and simian foamy virus has been found in
bushmeat hunters (Wolfe et al. 2004).
In recognition of the complexity of land
use change and the risks and benefits to
human health that it entails, a special collo-
quium titled “Unhealthy Landscapes: How
Land Use Change Affects Health” was con-
vened at the 2002 biennial meeting of the
International Society for Ecosystem Health
(6–11 June 2002, Washington, DC) to
address this issue. The invited experts worked
to establish consensus on the current state of
science and identify key knowledge gaps
underlying this issue. This article condenses
the working group’s report and presents a new
research and policy agenda for understanding
land use change and its effects on human
health. Specifically, we discuss land-use drivers
or human activities that exacerbate infectious
diseases; the land–water interface, common to
many infectious disease life cycles; and conclu-
sions and recommendations for research and
training from the working group.
Land-Use Drivers of Infectious
Disease Emergence
The emerging infectious diseases (EIDs)
resulting from land use change can be entirely
new to a specific location or host species. This
may occur either from “spillover” or cross-
species transmission or simply by extension of
geographic range into new or changed habi-
tats. More than 75% of human diseases are
zoonotic and have a link to wildlife and
domestic animals (Taylor et al. 2001).
Address correspondence to J.A. Patz, Center for
Sustainability and the Global Environment (SAGE),
Nelson Institute for Environmental Studies and the
Department of Population Health Sciences,
University of Wisconsin–Madison, 1710 University
Avenue, Room 202A, Madison, WI 53726-4087
USA. Telephone: (608) 265-9119. Fax: (608) 265-
4113. E-mail: jpatz@wisc.edu
Members of the Working Group on Land Use
Change and Disease Emergence, convened at the
biennial meeting of the International Society for
Ecosystem Health: A.A. Aguirre, F.P. Amerasinghe,
R.W. Ashford, D. Barthelemy, R. Bos, D.J. Bradley,
A. Buck, C. Butler, E.S. Chivian, K.B. Chua,
G. Clark, R. Colwell, U.E. Confalonieri, C. Corvalan,
A.A. Cunningham, P. Daszak, J. Dein, A.P. Dobson,
J.G. Else, J. Epstein, H. Field, J. Foufopoulos, P. Furu,
C. Gascon, D. Graham, A. Haines, A.D. Hyatt, A.
Jamaluddin, A.M. Kilpatrick, E.F. Kleinau, F. Koontz,
H.S. Koren, S. LeBlancq, S. Lele, S. Lindsay, N.
Maynard, R.G. McLean, T. McMichael, D.
Molyneux, S.S. Morse, D.E. Norris, R.S. Ostfeld, J.
Patz, M.C. Pearl, D. Pimentel, L. Rakototiana, O.
Randriamanajara, J. Riach, J.P. Rosenthal, E. Salazar-
Sanchez, E. Silbergeld, G.M. Tabor, M. Thomson,
A.Y. Vittor, N.D. Wolfe, L. Yameogo, and V. Zakarov.
Funding for the Special Colloquium, “Unhealthy
Landscapes: How Land Use Change Affects Health,”
was provided by the National Fish and Wildlife
Foundation, V. Kann Rasmussen Foundation,
Overbrook Foundation, and New York Community
Trust. The colloquium was cosponsored by the
World Health Organization and the United Nations
Environment Program.
The authors declare they have no competing financial
interests.
Received 25 November 2003; accepted 22 April
2004.
Unhealthy Landscapes: Policy Recommendations on Land Use Change and
Infectious Disease Emergence
Jonathan A. Patz,
1
Peter Daszak,
2
Gary M. Tabor,
3
A. Alonso Aguirre,
4
Mary Pearl,
4
Jon Epstein,
2
Nathan D. Wolfe,
5
A. Marm Kilpatrick,
2
Johannes Foufopoulos,
6
David Molyneux,
7
David J. Bradley,
8
and Members of the Working
Group on Land Use Change and Disease Emergence
1
Center for Sustainability and the Global Environment (SAGE), Nelson Institute for Environmental Studies and the Department of
Population Health Sciences, University of Wisconsin, Madison, Wisconsin, USA;
2
Consortium for Conservation Medicine, Palisades,
New York, USA;
3
Wilburforce Foundation, Bozeman, Montana, USA;
4
Wildlife Trust, Palisades, New York, USA;
5
Department of
Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, USA;
6
School of Natural Resources and
Environment, University of Michigan, Ann Arbor, Michigan, USA;
7
Lymphatic Filariasis Support Centre, Liverpool School of Tropical
Medicine, Liverpool, United Kingdom;
8
Centre on Global Change and Health, London School of Hygiene and Tropical Medicine, London,
United Kingdom
Anthropogenic land use changes drive a range of infectious disease outbreaks and emergence events
and modify the transmission of endemic infections. These drivers include agricultural encroach-
ment, deforestation, road construction, dam building, irrigation, wetland modification, mining, the
concentration or expansion of urban environments, coastal zone degradation, and other activities.
These changes in turn cause a cascade of factors that exacerbate infectious disease emergence, such
as forest fragmentation, disease introduction, pollution, poverty, and human migration. The
Working Group on Land Use Change and Disease Emergence grew out of a special colloquium
that convened international experts in infectious diseases, ecology, and environmental health to
assess the current state of knowledge and to develop recommendations for addressing these envi-
ronmental health challenges. The group established a systems model approach and priority lists of
infectious diseases affected by ecologic degradation. Policy-relevant levels of the model include spe-
cific health risk factors, landscape or habitat change, and institutional (economic and behavioral)
levels. The group recommended creating Centers of Excellence in Ecology and Health Research and
Training, based at regional universities and/or research institutes with close links to the surround-
ing communities. The centers’ objectives would be 3-fold: a) to provide information to local com-
munities about the links between environmental change and public health; b) to facilitate fully
interdisciplinary research from a variety of natural, social, and health sciences and train profession-
als who can conduct interdisciplinary research; and c) to engage in science-based communication
and assessment for policy making toward sustainable health and ecosystems. Key words: biodiver-
sity, deforestation, ecosystems, emerging infectious diseases, land use, Lyme disease, malaria, urban
sprawl, wildlife, zoonosis. Environ Health Perspect 112:1092–1098 (2004). doi:10.1289/ehp.6877
available via http://dx.doi.org/ [Online 22 April 2004]
Research
Meeting Report
The working group developed an extensive
list of processes by which land use affects
human health (specifically, infectious disease
occurrence) and of other factors that contribute
to this relationship: agricultural development,
urbanization, deforestation, population move-
ment, increasing population, introduction of
novel species/pathogens, water and air pollu-
tion, biodiversity loss, habit fragmentation,
road building, macro and micro climate
changes, hydrological alteration, decline in
public health infrastructure, animal-intensive
systems, eutrophication, military conflict,
monocropping, and erosion (ranked from high-
est to lowest public health impact by meeting
participants). The four mechanisms that were
felt to have the greatest impact on public
health were changes to the physical environ-
ment; movement of populations, pathogens,
and trade; agriculture; and urbanization. War
and civil unrest were also mentioned as a
potentially acute and cross-cutting driver.
Infectious disease agents with the strongest
documented or suspected links to land use
change are listed in Table 1.
Changes to the biophysical environment.
Deforestation. Rates of deforestation have
grown exponentially since the beginning of
the 20th century. Driven by rapidly increasing
human population numbers, large swaths of
species-rich tropical and temperate forests, as
well as prairies, grasslands, and wetlands, have
been converted to species-poor agricultural
and ranching areas. The global rate of tropical
deforestation continues at staggering levels,
with nearly 2–3% of forests lost globally each
year. Parallel with this habitat destruction is an
exponential growth in human–wildlife interac-
tion and conflict. This has resulted in expo-
sure to new pathogens for humans, livestock,
and wildlife (Wolfe et al. 2000). Deforestation
and the processes that lead to it have many
consequences for ecosystems. Deforestation
decreases the overall habitat available for
wildlife species. It also modifies the structure
of environments, for example, by fragmenting
habitats into smaller patches separated by agri-
cultural activities or human populations.
Increased “edge effect” (from a patchwork of
varied land uses) can further promote interac-
tion among pathogens, vectors, and hosts.
This edge effect has been well documented for
Lyme disease (Glass et al. 1995). Similarly,
increased activity in forest habitats (through
behavior or occupation) appears to be a major
risk factor for leishmaniasis (Weigle et al.
1993). Evidence is mounting that deforesta-
tion and ecosystem changes have implications
for the distribution of many other microor-
ganisms and the health of human, domestic
animal, and wildlife populations.
One example of the effects of land use
on human health is particularly noteworthy.
Deforestation, with subsequent changes in
land use and human settlement patterns, has
coincided with an upsurge of malaria and/or its
vectors in Africa (Coluzzi 1984, 1994; Coluzzi
et al. 1979), in Asia (Bunnag et al. 1979), and
in Latin America (Tadei et al. 1998). When
tropical forests are cleared for human activities,
they are typically converted into agricultural or
grazing lands. This process is usually exacer-
bated by construction of roads, causing erosion
and allowing previously inaccessible areas to
become colonized by people (Kalliola and
Flores Paitán 1998). Cleared lands and culverts
that collect rainwater are in some areas far
more suitable for larvae of malaria-transmitting
anopheline mosquitoes than are intact forests
(Charlwood and Alecrim 1989; Jones 1951;
Marques 1987).
Another example of the effects of land use
on human health involves deforestation and
noninfectious disease: the contamination of
rivers with mercury. Soil erosion after defor-
estation adds significant mercury loads, which
are found naturally in rainforest soils, to
rivers. This has led to fish in the Amazon
becoming hazardous to eat (Fostier et al.
2000; Veiga et al. 1994).
Habitat fragmentation. This alters the
composition of host species in an environment
and can change the fundamental ecology of
microorganisms. Because of the nature of food
webs within ecosystems, organisms at higher
trophic levels exist at a lower population den-
sity and are often quite sensitive to changes in
food availability. The smaller patches left after
fragmentation often do not have sufficient prey
for top predators, resulting in local extinction
of predator species and a subsequent increase
in the density of their prey species. Logging
and road building in Latin America have
increased the incidence of cutaneous and vis-
ceral leishmaniasis (Desjeux 2001), which in
some areas has resulted from an increase in the
number of fox reservoirs and sandfly vectors
that have adapted to the peridomestic environ-
ment (Patz et al. 2000). Foxes, however, are
not very important reservoirs for leishmaniasis
in Latin America (Courtenay et al. 2002), and
a more important factor in the transmission
cycle includes domestic dogs.
Ostfeld and Keesing (2000) have demon-
strated that smaller fragments in North
American forests have fewer small mammal
predators. Results suggest that the probability
that a tick will become infected depends on
not only the density of white-footed mice but
also the density of mice relative to that of other
hosts in the community. Under this scenario,
the density effect of white-footed mice, which
are efficient reservoirs for Lyme disease, can be
“diluted” by an increasing density of alternative
hosts, which are less efficient at transmitting
Lyme disease. These results suggest that
increasing host diversity (species richness) may
decrease the risk of disease through a “dilution
effect” (Schmidt and Ostfeld 2001).
Extractive industries. Gold mining is an
extractive industry that damages local and
regional environments and has adverse human
health effects, because mercury is used to
extract gold from riverbeds in the tropical
forests. Not only does mercury accumulate in
local fish populations, making them toxic to
eat (Lebel et al. 1996, 1998), but mercury also
suppresses the human immune system. Also,
in gold-mining areas, more mosquito-breeding
sites and increased malaria risk result from
digging gem pits in the forest and from craters
resulting from logging; broader disease spread
occurs as populations disperse throughout the
region (Silbergeld et al. 2002).
Movement of populations, pathogens, and
trade. The movement of humans, domestic
animals, wildlife populations, and agricultural
products through travel, trade, and transloca-
tions is a driver of infectious disease emer-
gence globally. These sometimes inadvertent,
sometimes deliberate movements of infectious
disease and vectors (e.g., the introduction of
Meeting Report
|
Land use change and infectious disease emergence
Environmental Health Perspectives
VOLUME 112 | NUMBER 10 | July 2004
1093
Table 1. Agents and infectious diseases with suspected or known links to landscape change.
a
Vector-borne
and/or zoonotic Soil Water Human Other
Malaria Melioidosis Schistosomiasis Asthma Hemorrhagic fevers
Dengue Anthrax Cholera Tuberculosis Foot and mouth
Lyme disease Hookworm Shigellosis Influenza Rice blast
Yellow fever Coccidioidomycosis Rotavirus Triachoma
Rift Valley fever Salmonellosis
Japanese encephalitis Leptospirosis
Onchocerciasis Cryptosporidiosis
Trypanosomiasis
Plague
Filariasis
Meningitis
Rabies
Leishmaniasis
Kyasanur Forest fever
Hantavirus
Nipah virus
a
Those with the strongest evidence for a link with land use.
smallpox and measles to the Americas by
Spanish conquistadors) will continue to rise
via continually expanding global travel and by
development of Third World populations.
Human introduction of pathogens, hosts, or
materials into new areas has been termed
“pathogen pollution” (Daszak et al. 2000).
Land use changes drive some of these intro-
ductions and migrations and also increase the
vulnerability of habitats and populations to
these introductions. Human migrations also
drive land use changes that in turn drive infec-
tious disease emergence. For example, in
China’s Yunnan Province, an increase in live-
stock populations and migration has led to an
increase in the incidence of schistosomiasis
(Jiang et al. 1997). In Malaysia, a combination
of deforestation, drought, and wildfires has led
to alterations in the population movements
and densities of flying foxes, large fruit bats
known to be the reservoir for the newly emer-
gent zoonosis Nipah virus (Chua et al. 1999).
It is believed that the increased opportunity for
contact between infected bats and pigs pro-
duced the outbreak of the disease in pigs,
which then was transmitted to people in con-
tact with infected pigs (Aziz et al. 2002).
Another example of human-induced ani-
mal movement on a much larger scale is the
international pet trade. This movement of ani-
mals involves many countries and allows for
the introduction of novel pathogens, such as
monkeypox, with the potential to damage
ecosystems and threaten human and animal
health. Monkeypox was originally associated
with bushmeat hunting of red colobus mon-
keys (Procolobus badius); after a localized epi-
demic emerged in humans, monkeypox
persisted for four generations via human-to-
human contact (Jezek et al. 1986).
Human movement also has significant
implications for public health. Not only are
travelers (tourists, businesspeople, and other
workers) at risk of contracting communicable
diseases when visiting tropical countries, but
they also can act as vectors for delivering
infectious diseases to another region or, in the
case of severe acute respiratory syndrome
(SARS), potentially around the world.
Refugees account for a significant number of
human migrants, carrying diseases such as
hepatitis B and tuberculosis and various para-
sites (Loutan et al. 1997). Because of their
status, refugees become impoverished and are
more exposed to a wide range of health risks.
This is caused by the disruption of basic
health services, inadequate food and medical
care, and lack of clean water and sanitation
(Toole and Waldman 1997). People who cross
international boundaries, such as travelers,
immigrants, and refugees, may be at increased
risk of contracting infectious diseases, espe-
cially those who have no immunity because
the disease agents are uncommon in their
native countries. Immigrants may come from
nations where diseases such as tuberculosis and
malaria are endemic, and refugees may come
from situations where crowding and malnutri-
tion create ideal conditions for the spread of
diseases such as cholera, shigellosis, malaria,
and measles [Centers for Disease Control and
Prevention (CDC) 1998].
Zoonoses. The importance of zoonotic
diseases should be emphasized. Zoonotic
pathogens are the most significant cause of
EIDs affecting humans, both in the propor-
tion of EIDs that they cause and in the impact
that they have. Some 1,415 species of infec-
tious organisms are known to be pathogenic to
people, with 61% of them being zoonotic. Of
the emerging pathogens, 75% are zoonotic,
and zoonotic pathogens are twice as likely to
be associated with emerging diseases than are
nonzoonotic pathogens (Taylor et al. 2001).
More important, zoonotic pathogens cause a
series of EIDs with high case fatality rates and
no reliable cure, vaccine, or therapy (e.g.,
Ebola virus disease, Nipah virus disease, and
hantavirus pulmonary syndrome). Zoonotic
pathogens also cause diseases that have some
of the highest incidence rates globally [e.g.,
acquired immunodeficiency syndrome
(AIDS)]. AIDS is a special case, because it is
caused by a pathogen that jumped host from
nonhuman primates and then evolved into a
new virus. Thus, it is in origin a zoonotic
organism (Hahn et al. 2000).
Because of the important role of zoonoses
in current public health threats, wildlife and
domestic animals play a key role in the
process by providing a “zoonotic pool” from
which previously unknown pathogens may
emerge (Daszak et al. 2001). The influenza
virus is an example, causing pandemics in
humans after periodic exchange of genes
among the viruses of wild and domestic birds,
pigs, and humans. Fruit bats are involved in a
high-profile group of EIDs that includes
rabies and other lyssaviruses, Hendra virus
and Menangle virus (Australia), and Nipah
virus (Malaysia and Singapore), which has
implications for further zoonotic disease
emergence. A number of species are endemic
to both remote oceanic islands and more pop-
ulous suburban and rural human settlements;
these may harbor enzootic and potentially
zoonotic pathogens with an unknown poten-
tial for spillover (Daszak et al. 2000).
Thus, some of the current major infec-
tious threats to human health are EIDs and
reemerging infectious diseases, with a particu-
lar emphasis on zoonotic pathogens transfer-
ring hosts from wildlife and domestic
animals. A common, defining theme for most
EIDs (of humans, wildlife, domestic animals,
and plants) is that they are driven to emerge
by anthropogenic changes to the environ-
ment. Because threats to wildlife habitat are
so extensive and pervading, many of the cur-
rently important human EIDs (e.g., AIDS,
Nipah virus disease) are driven partly by
human-induced changes to wildlife habitat
such as encroachment and deforestation. This
is essentially a process of natural selection in
which anthropogenic environmental changes
perturb the host–parasite dynamic equilib-
rium, leading to the expansion of those strains
suited to the new environmental conditions
and facilitating expansion of others into new
host species (Daszak et al. 2001).
Agriculture. Crop irrigation and breeding
sites. Agriculture occupies about half of the
world’s land and uses more than two-thirds of
the world’s fresh water (Horrigan et al. 2002).
Agricultural development in many parts of the
world has increased the need for crop irriga-
tion, which reduces water availability for other
uses and increases breeding sites for disease
vectors. An increase in soil moisture associated
with irrigation development in the southern
Nile Delta after the construction of the Aswan
High Dam has caused a rapid rise in the mos-
quito Culex pipiens and consequential increase
in the arthropod-borne disease Bancroftian
filariasis (Harb et al. 1993; Thompson et al.
1996). Onchocerciasis and trypanosomiasis
are further examples of vector-borne parasitic
diseases that may be triggered by changing
land-use and water management patterns. In
addition, large-scale use of pesticides has had
deleterious effects on farm workers, including
hormone disruption and immune suppression
(Straube et al. 1999).
Food-borne diseases. Once agricultural
development has expanded and produced
food sufficient to meet local need, the food
products are exported to other nations, where
they can pose a risk to human health. The
increase in imported foods has resulted in a
rise in food-borne illness in the United States.
Strawberries from Mexico, raspberries from
Guatemala, carrots from Peru, and coconut
milk from Thailand have caused recent out-
breaks. Food safety is an important factor in
human health, because food-borne disease
accounts for an estimated 76 million illnesses,
325,000 hospitalizations, and 5,200 deaths in
the United States each year (CDC 2003).
Other dangers include antibiotic-resistant
organisms, such as Cyclospora, Escherichia coli
O157:H7, and other pathogenic E. coli
strains associated with hemolytic uremic syn-
drome in children (Dols et al. 2001).
Secondary effects. Agricultural secondary
effects need to be minimized, such as the
emerging microbial resistance from antibiotics
in animal waste that is included in farm runoff
and the introduction of microdams for irri-
gation in Ethiopia that resulted in a 7-fold
increase in malaria (Ghebreyesus et al. 1999).
Urbanization. On a global basis, the pro-
portion of people living in urban centers will
Meeting Report
|
Patz et al.
1094
VOLUME 112 | NUMBER 10 | July 2004
Environmental Health Perspectives
increase to an unprecedented 65% by the year
2030 (Population Reference Bureau 1998).
The 2000 census shows that 80% of the U.S.
population now lives in metropolitan areas,
with 30% living in cities of 5 million or
more. The environmental issues posed by
such large population centers have profound
impacts on public health beyond the city lim-
its (Knowlton 2001).
Alterations of ecosystems and natural
resources contribute to the emergence and
spread of infectious disease agents. Human
encroachment of wildlife habitat has broad-
ened the interface between wildlife and
humans, increasing opportunities for both the
emergence of novel infectious diseases in
wildlife and their transmission to people.
Rabies is an example of a zoonotic disease car-
ried by animals that has become habituated to
urban environments. Bats colonize buildings,
skunks and raccoons scavenge human refuse,
and in many countries feral dogs in the streets
are common and the major source of human
infection (Singh et al. 2001).
Infectious diseases can also pass from
people to wildlife. Nonhuman primates have
acquired measles from ecotourists (Wallis
and Lee 1999). Also, drug resistance in gram-
negative enteric bacteria of wild baboons
living with limited human contact is signifi-
cantly less common than in baboons living
with human contact near urban or semiurban
human settlements (Rolland et al. 1985).
The Land–Water Interface
Another major driver of infectious disease
emergence results from the land–water inter-
face. Land use changes often involve water
projects or coastal marine systems in which
nutrients from agricultural runoff can cause
algal blooms.
Currently the seventh cholera pandemic
is spreading across Asia, Africa, and South
America. In 1992, a new serogroup (Vibrio
cholerae O139) appeared and has been respon-
sible for epidemics in Asia (Colwell 1996). The
seasonality of cholera epidemics may be linked
to the seasonality of plankton (algal blooms)
and the marine food chain. Studies using
remote-sensing data of chlorophyll-containing
phytoplankton have shown a correlation
between cholera cases and sea surface tempera-
tures in the Bay of Bengal. Interannual vari-
ability in cholera incidence in Bangladesh is
also linked to the El Niño southern oscillation
and regional temperature anomalies (Lobitz
et al. 2000), and cholera prevalence has been
associated with progressively stronger El Niño
events spanning a 70-year period (Rodo et al.
2002). This observation on cholera incidence
may represent an early health indicator of
global climate change (Patz 2002).
Infectious diseases in marine mammals and
sea turtles could serve as sentinels for human
disease risk. Sea turtles worldwide are affected
by fibropapillomatosis, a disease probably
caused by one or several viruses and character-
ized by multiple epithelial tumors. Field stud-
ies support the observation that prevalence of
this disease is associated with heavily polluted
coastal areas, areas of high human density, agri-
cultural runoff, and/or biotoxin-producing
algae (Aguirre and Lutz, in press). This repre-
sents the breakdown of the land–water inter-
face, to the point that several pathogens typical
of terrestrial ecosystems have become estab-
lished in the oceans. Toxoplasmosis in the
endangered sea otter (Enhydra lutris) represents
an example of pathogen pollution. Massive
mortalities in pinnipeds and cetaceans reaching
epidemics of tens of thousands are caused
by four morbilliviruses evolving from the
canine distemper virus (Aguirre et al. 2002).
Additionally, overfishing has myriad ramifica-
tions for marine ecosystems and sustainable
protein food sources for human populations.
Cryptosporidium, a protozoan that com-
pletes its life cycle within the intestine of mam-
mals, sheds high numbers of infectious oocysts
that are dispersed in feces. A recent study
found that 13% of finished treated water still
contained Cryptosporidium oocysts, indicating
some passage of microorganisms from source
to treated drinking water (LeChevallier and
Norton 1995). The protozoan is highly preva-
lent in ruminants and is readily transmitted to
humans. Thus, management of livestock cont-
amination of watersheds is an important public
health issue.
One example of how overexploitation of a
natural water resource led to infectious disease
is that of Lake Malawi in Africa. Overfishing
in the lake reduced the population of snail-
eating fish to such a level that snail popula-
tions erupted. Subsequently, schistosomiasis
incidence and prevalence markedly rose after
this ecologic imbalance (Madsen et al. 2001).
Recommendations from the
Working Group
Conceptual model: bringing land use into pub-
lic health policy. The recommendations stem-
ming from the international colloquium are
highly relevant to the Millennium Ecosystem
Assessment (MEA), a broad multiagency/foun-
dation-sponsored scientific assessment of
degraded ecosystem effects on human well-
being. A conceptual framework of the MEA
already provides an approach to optimize the
contribution of ecosystems to human health
(MEA 2003). This framework offers a mecha-
nism to a) identify options that can better
achieve human development and sustainable
goals, b) better understand the trade-offs
involved in environment-related decisions, and
c) align response options at all scales, from the
local to the global, where they can be most
effective. This conceptual framework focuses
on human well-being while also recognizing
associated intrinsic values. Similar to the
MEA, focus is particularly on the linkages
between ecosystem services and human health.
Workshop participants developed a conceptual
model (Figure 1). Like the MEA, it assumes a
dynamic interaction between humans and
ecosystems that warrants a multiscale assess-
ment (spatial and temporal).
By using this framework, policy makers
may approach development and health at var-
ious levels. These levels include specific health
risk factors, landscape or habitat change, and
institutional (economic and behavioral) levels.
For sound health policy, we must shift away
from dealing primarily with specific risk
factors and look “upstream” to underlying
land-use determinants of infectious disease
and ultimately the human behavior and estab-
lished institutions that are detrimental to
sustainable population health. The World
Health Organization (WHO) has developed a
similar DPSEEA (driving forces, pressures,
state, exposure, effect, actions) model that in a
similar way describes the interlinkage between
human health and different driving forces and
environmental change (WHO 1997).
As such understanding increases, it will
become more feasible to plan how to prevent
new infectious disease emergence. Yet, because
these are rare events, accurate predictions will
remain daunting. It is already evident that
inserting humans into complex ecosystems can
lead to a variety of EIDs, but health outcomes
depend on the economic circumstances of the
human population. In poor and tropical com-
munities, land use change can lead to major
shifts in infectious disease patterns. For these
situations, many conventional public health
interventions can prevent several infectious
diseases at relatively low cost. In rich and tem-
perate-climate communities, the infectious
disease shifts tend to be more disease specific,
for example, in the case of Lyme disease and
habitat fragmentation.
Research on deforestation and infectious
disease. Considering the deforestation that
usually accompanies agricultural development,
new conservation-oriented agriculture should
be pursued. As discussed above, water project
development and modern livestock manage-
ment present major health disease risks.
However, often the secondary unintended
consequences can also wreak havoc; for exam-
ple, a leaking dam may present greater risks
than the reservoir itself. A distressingly large
number of development projects not only
have adverse effects on human health but also
fail to attain their primary economic purposes
in a sustainable manner.
Habitat fragmentation, whether caused by
forest destruction, desertification, or land-use
conversion, affects human and wildlife health
and ecosystem processes. There is already
Meeting Report
|
Land use change and infectious disease emergence
Environmental Health Perspectives
VOLUME 112 | NUMBER 10 | July 2004
1095
much research undertaken by landscape ecolo-
gists on the consequences of habitat fragmenta-
tion for wildlife, especially larger animals. It
would be important to study the effects of
landscape fragmentation on public health haz-
ards. Such research could entail three com-
ponents. The first component consists of
gathering baseline data, including using histori-
cal data where possible and beginning moni-
toring programs where necessary. Key data
include identifying and quantifying the rele-
vant pathogen load of wildlife, livestock, and
human communities in fragmented landscapes.
The goals of this data collection are, first, to
identify key infectious diseases, both chronic
and emergent or reemergent and, second, to
document the consequences of fragmentation
on relative abundance of wildlife and subse-
quent pathogen load. For example, the loss of
large predators in fragmented habitats in the
northeastern United States has led to a super-
abundance of rodent vectors for Lyme disease.
The second component of the research pro-
gram would involve health impact modeling,
primarily in three areas: a) estimating changes
in the relative abundance of organisms, includ-
ing infectious disease vectors, pathogens, and
hosts; b) projecting potential vector or transmis-
sion shifts (e.g., should the Nipah virus shift to
pulmonary as well as neurologic expression in
humans as in swine); and c) projecting the
impact of infectious diseases in a region on
different geographic scales.
The results of these analyses, if successful,
could support the third component of
research: development of decision-support
tools. Improved decisions on land-use policy
could be made from a better understanding of
costs and benefits to health and environmental
decision makers. In all probability, however,
they will be very location specific. For example,
to construct an irrigation scheme in India
would likely invite a malaria epidemic, whereas
the same activity in sub-Saharan Africa may
have little effect on malaria transmission. It is
worth mentioning that costs and benefits could
depend on the time course over which they are
assessed. For example, some land-use changes
can lead to short-term increases in transmission
followed by longer-term decreases (e.g., irriga-
tion and malaria in Sri Lanka) or vice versa
(e.g., deforestation and cutaneous leishmaniasis
in Latin America).
Policies to reduce microbial traffic/
pathogen pollution. In today’s interconnected
world, it becomes very important to invest in
the worldwide control of infectious diseases in
developing countries, for example. It is also
necessary to control transport to stem the flow
from one place to the next.
Improved monitoring of trade is war-
ranted in order to target infectious disease
introductions. In the attempt to prevent the
invasion of a pathogen (and drug-resistant
organisms) into the vulnerable areas subject to
land use changes, we need to pay greater atten-
tion to controls at the sources. We need to
document and map these trades and investi-
gate the vectors, the infectious diseases they
harbor, and the populations they threaten.
Risk assessment should guide surveillance and
the development of test kits, targeting point-
of-origin intervention to preempt these
processes. Assessments must further include
nonmarket costs (usually to the detriment of
the environment and long-term sustainable
health). We should communicate to both the
exporters and consumers the need to make
their trades clean, economically viable, and
certified “clean and green” by an independent
scientific agency at the source and/or destina-
tion. Additionally, strategies for screening
travelers for pathogens that may be introduced
to a region should be improved.
Centers of Excellence in Ecology and
Health Research and Training. One approach
to developing the issues to which this article
draws attention is the creation of a system of
regional- or subregional-based interdiscipli-
nary Centers of Excellence in Ecology and
Health Research and Training. Based at
regional universities and/or research institutes
but with very close links to the surrounding
communities, these centers would have the
following objectives:
Providing information based on good sci-
ence to local communities about the links
between environmental change and public
health, including the factors that contribute
to specific infectious disease outbreaks. The
new research agenda must gather informa-
tion on household and community perspec-
tives about proposals for the use of their
land. These perspectives are key to assessing
the cost/benefit of a proposed project.
Training local professionals in environmen-
tal, agricultural, and health science issues,
with a particular focus on granting degrees
in a new “trans”-discipline linking health
and the environment, would be emphasized.
Acting as centers of integrated analysis of
infectious disease emergence, incorporating
perspectives and expertise from a variety of
natural, social, and health sciences. Research
activities would range from taxonomy of
pathogens and vectors to identifying best
practices for influencing changes in human
behavior to reduce ecosystem and health risks.
Incorporating a “health impact assessment”
as an important cross-sectorial decision-
making tool in overall development plan-
ning (parallel to an environmental impact
Meeting Report
|
Patz et al.
1096
VOLUME 112 | NUMBER 10 | July 2004
Environmental Health Perspectives
Figure 1. A systems model of land use change that affects public health. This model shows relationships
between drivers of land use change and subsequent levels of environmental change and health conse-
quences. Various levels of investigation and intervention are evident and range from specific risks factors
and determinants of population vulnerability to larger institutional and economic activity.
Wealth–poverty status
Exogenous
variables
Primary
determinant
Economic activity
Climate
change
Resource
consumption
Possibility of
economic gain
Proximate
determinants
Ecological factors Factors facilitating exploitation of resources
Land use
change
Biodiversity Habitat
Ecosystem
services
Policy Technology Infrastructure
Agriculture
Extractive enterprises
Habitat fragmentation, deforestation
Human settlement
Land/water interface (coastal and watershed)
Movement of populations, trade, and pathogens
Intervening
variables
Ecological effects Human behavior
Biodiversity Climate Habitat
Ecosystem
services
Pathogen presence and dynamics
Outcomes of
health
revelance
Health impact
Pathogenicity
Means of
transmission
Susceptible populations
(to infection and disease)
Cases of disease
Biome
Presence
of natural
resources
Human
population
dynamics
Exposure to
environments
with pathogens
Disease
risk-reduction
practices
Health care
system
assessment), along with the need for doing
more research.
Equipping professionals with the ability to
recommend policy toward maintaining
ecosystem function and promoting sustain-
able public health for future generations. For
example, the link between forest fragmenta-
tion and Lyme disease risk could lead to pre-
serving more intact tracts of forest habitat by
planning “cluster” housing schemes.
Implementing research and policy pro-
grams. In selecting areas for research and the
placement of centers of excellence, it is impor-
tant to choose geographically representative,
highly diverse areas around the world. In addi-
tion, research projects should take place in
regions or landscapes that have both well char-
acterized and less characterized patterns of
infectious disease emergence or transmission
for comparison purposes. Local health and
environment professionals, who are in the best
position to understand local priorities, should
make the choices within each region for initial
research areas and sites.
Addressing trade-offs among environ-
ment, health, and development. There are
some inherent trade-offs when considering
land-use change and health. They are ethical
values, environmental versus health choices,
and disparities in knowledge and economic
class. Trade-offs are between short-term bene-
fit and long-term damage. For example, drain-
ing swamps may reduce vector-borne disease
hazards but also destroy the wetland ecosystem
and its inherent services (e.g., water storage,
water filtration, biologic productivity, and
habitats for fish and wildlife). Research can
help decision making by identifying and
assessing trade-offs in different land-use-
change scenarios. Balancing the diverse needs
of people, livestock, wildlife, and the ecosys-
tem will always be a prominent feature.
Conclusions
When considering issues of land use and
infectious disease emergence, the public needs
to be attentive to entire ecosystems rather
than simply their local environs. Although we
may not live within a certain environment,
its health may indirectly affect our own. For
example, intact forests support complex
ecosystems and provide essential habitats for
species that are specialized to those flora and
that may be relevant to our health. If these
complex relationships are disrupted, there
may be unforeseen impacts on human health,
as the above examples clearly demonstrate.
Encouraging initiatives. Three new initia-
tives are rising to the challenges presented
above. The first initiative, the Consortium for
Conservation Medicine (CCM), was formed
recently to address these health challenges at the
interface of ecology, wildlife health, and public
health (Figure 2). At its core, conservation med-
icine champions the integration of techniques
and partnering of scientists from diverse disci-
plines, particularly veterinary medicine, conser-
vation biology, and public health. Through the
consortium, therefore, these experts work with
educators, policy makers, and conservation pro-
gram managers to devise approaches that
improve the health of both species and humans
simultaneously [more information is available
from the CCM website (CCM 2004)].
The second initiative, the new international
journal EcoHealth, focuses on the integration of
knowledge at the intersection of ecologic and
health sciences. The journal provides a gather-
ing place for research and reviews that integrate
the diverse knowledge of ecology, health, and
sustainability, whether scientific, medical, local,
or traditional. The journal will encourage devel-
opment and innovation in methods and prac-
tice that link ecology and health, and it will
ensure clear and concise presentation to facili-
tate practical and policy application [more
information is available from
the EcoHealth
website (
EcoHealth 2004)].
The third initiative, the MEA, is an inter-
national work program designed to meet the
needs of decision makers and the public for
scientific information concerning the conse-
quences of ecosystem change for human
health and well-being and for options in
responding to those changes. This assessment
was launched by United Nations Secretary-
General Kofi Annan in June 2001 and will
help to meet the assessment needs of interna-
tional environmental forums, such as the
Convention on Biological Diversity, the
Convention to Combat Desertification, the
Ramsar Convention on Wetlands, and the
Convention on Migratory Species, as well as
the needs of other users in the private sector
and civil society [more information is available
from
the
Millennium Assessment Working
Groups website
(
Millennium Assessment
Working Groups 2004)].
Challenges ahead. As this working group of
researchers continues to work on these topics,
we face three challenges. First, strong trans-
disciplinary research partnerships need to be
forged to approach the research with the
degree of creative thinking and comprehen-
siveness required by the nature of the prob-
lems. Second, if the work is to influence policy,
the choice of questions and the research must
be undertaken collaboratively with the local
community and also through discussion with
decision makers in government, industry, civil
society, and other sectors. Third, investigators
must consider how they can integrate their
findings into the social, economic, and political
dialogue on both the environment and health,
globally and locally. As links between land use
and health are elucidated, an informed public
will more readily use such discoveries to better
generate political will for effective change.
REFERENCES
Aguirre AA, Lutz P. In press. Marine turtles as sentinels of
ecosystem health: is fibropapillomatosis an indicator?
EcoHealth.
Aguirre AA, Ostfeld RS, Tabor GM, House C, Pearl MC (eds.).
2002. Conservation Medicine: Ecological Health in
Practice. New York:Oxford University Press.
Aziz AJ, Nor SK, Chua KB, Shamshad S. 2002. Emerging
Infectious Diseases—A Malaysian Perspective. Tokyo:OIE
Regional Representation for Asia and the Pacific. Available:
http://www.rr-asia.oie.int/topics/detail011_03.html
[accessed 10 April 2003].
Bunnag T, Sornmani S, Pinithpongse S, Harinasuta C. 1979.
Meeting Report
|
Land use change and infectious disease emergence
Environmental Health Perspectives
VOLUME 112 | NUMBER 10 | July 2004
1097
Figure 2. The main elements converging under the Consortium for Conservation Medicine. Conservation medi-
cine combines conservation biology, wildlife veterinary medicine, and public health. Adapted from Tabor (2002).
Translocation
Human
encroachment
Domestic animal
encroachment
Technology and
industry
“Spillover”
introduction
Natural
resource
extraction
Biodiversity
loss
Agricultural
intensification
Global travel
Urbanization
Biochemical
manipulation
Wildlife and
domestic animal
diseases
Ecosystem
functioning
Human
diseases
Conservation medicine
Meeting Report
|
Patz et al.
1098
VOLUME 112 | NUMBER 10 | July 2004
Environmental Health Perspectives
Surveillance of water-borne parasitic infections and studies
on the impact of ecological changes on vector mosquitoes
of malaria after dam construction. Southeast Asian J Trop
Med Public Health 10:656–660.
CCM. 2004. Conservation Medicine. Palisades, NY:Consortium
for Conservation Medicine. Available: http://www.
conservationmedicine.org/ [accessed 10 May 2003].
CDC. 1998. Addressing the problem of diseases of travelers,
immigrants, and refugees. In: Emerging Infectious Diseases:
A Strategy for the 21st Century. Atlanta, GA:National Center
for Infectious Diseases, Centers for Disease Control
and Prevention. Available: http://www.cdc.gov/ncidod/
emergplan/travel/page_2.htm [accessed 10 May 2003].
CDC. 2003. Foodborne Illness. Atlanta, GA:Division of Bacterial
and Mycotic Diseases, National Center for Infectious
Diseases, Centers for Disease Control and Prevention.
Available: http://www.cdc.gov/ncidod/dbmd/diseaseinfo/
foodborneinfections_g.htm [accessed 10 May 2003].
Charlwood JD, Alecrim WA. 1989. Capture-recapture studies
with the South American malaria vector Anopheles darlingi,
Root. Ann Trop Med Parasitol 83:569–576.
Chua KB, Goh KJ, Wong KT, Kamarulzaman A, Tan PS, Ksiazek
TG, et al. 1999. Fatal encephalitis due to Nipah virus among
pig-farmers in Malaysia. Lancet 354:1257–1259.
Coluzzi M. 1984. Heterogeneities of the malaria vectorial system
in tropical Africa and their significance in malaria epidemiol-
ogy and control. Bull WHO 62(suppl):107–113.
Coluzzi M. 1994. Malaria and the Afrotropical ecosystems: impact
of man-made environmental changes. Parassitologia
36:223–227.
Coluzzi M, Sabatini A, Petrarca V, Di Deco MA. 1979. Chromosomal
differentiation and adaptation to human environments in the
Anopheles gambiae complex. Trans R Soc Trop Med Hyg
73:483–497.
Colwell RR. 1996. Global climate and infectious disease: the
cholera paradigm. Science 274:2025–2031.
Courtenay O, Quinnell RJ, Garcez LM, Dye C. 2002. Low infec-
tiousness of a wildlife host of Leishmania infantum: the
crab-eating fox is not important for transmission.
Parasitology 125(pt 5):407–414.
Daszak P, Cunningham AA, Hyatt AD. 2000. Emerging infectious
diseases of wildlife—threats to biodiversity and human
health. Science 287:443–449.
Daszak P, Cunningham AA, Hyatt AD. 2001. Anthropogenic
environmental change and the emergence of infectious
diseases in wildlife. Acta Trop 78:103–116.
Desjeux P. 2001. The increase in risk factors for leishmaniasis
worldwide. Trans R Soc Trop Med Hyg 95(3):239–243.
Dols CL, Bowers JM, Copfer AE. 2001. Preventing food- and
water-borne illnesses. Am J Nurs 101:24AA–24HH.
EcoHealth. 2004. Conservation Medicine, Human Health,
Ecosystem Sustainability. New York:Springer Verlag.
Available: http://www.ecohealth.net/ [accessed 4 April
2003].
Fostier AH, Forti MC, Guimaraes JR, Melfi AJ, Boulet R,
Espirito Santo CM, et al. 2000. Mercury fluxes in a natural
forested Amazonian catchment (Serra do Navio, Amapa
State, Brazil). Sci Total Environ 260:201–211.
Ghebreyesus TA, Haile M, Witten KH, Getachew A, Yohannes
AM, Yohannes M, et al. 1999. Incidence of malaria among
children living near dams in northern Ethiopia: community
based incidence survey. BMJ 319:663–666.
Glass GE, Schwartz BS, Morgan JM III, Johnson DT, Noy PM,
Israel E. 1995. Environmental risk factors for Lyme disease
identified with geographic information systems. Am J
Public Health 85:944–948.
Hahn BH, Shaw GM, De Cock KM, Sharp PM. 2000. AIDS as a
zoonosis: scientific and public health implications. Science
287:607–614.
Harb M, Faris R, Gad AM, Hafez ON, Ramzy R, Buck AA. 1993.
The resurgence of lymphatic filariasis in the Nile delta.
Bull WHO 71:49–54.
Horrigan L, Lawrence RS, Walker P. 2002. How sustainable agri-
culture can address the environmental and human health
harms of industrial agriculture. Environ Health Perspect
110:445–456.
Jezek Z, Arita I, Mutombo M, Dunn C, Nakano JH, Szczeniowski
M. 1986. Four generations of probable person-to-person
transmission of human monkeypox. Am J Epidemiol
123:1004–1012.
Jiang Z, Zheng QS, Wang XF, Hua ZH. 1997. Influence of live-
stock husbandry on schistosomiasis transmission in
mountainous regions of Yunnan Province. Southeast Asian
J Trop Med Public Health 28:291–295.
Jones TW. 1951. Deforestation and epidemic malaria in the
wet and intermediate zones of Ceylon. Indian J Malariol
5:135–161.
Kalliola R, Flores Paitán S (eds.). 1998. Geoecología y Desarrollo
Amazónico. Estudio Integrado en la Zona de Iquitos, Perú.
Sulkava, Peru:Finnreklama Oy.
Knowlton K. 2001. Urban history, urban health. Am J Public
Health 91:1944–1946.
Lam SK, Chua KB. 2002. Nipah virus encephalitis outbreak in
Malaysia. Clin Infect Dis 34(suppl 2):S48–S51.
Lebel J, Mergler D, Branches F, Lucotte M, Amorim M, Larribe F,
et al. 1998. Neurotoxic effects of low-level methylmercury
contamination in the Amazonian Basin. Environ Res
79:20–32.
Lebel J, Mergler D, Lucotte M, Amorim M, Dolbec J, Miranda D,
et al. 1996. Evidence of early nervous system dysfunction in
Amazonian populations exposed to low-levels of methyl-
mercury. Neurotoxicology 17:157–167.
LeChevallier MW, Norton WD. 1995. Giardia and cryptosporid-
ium in raw and finished water. J Am Water Works Assoc
87:54–68.
Lobitz B, Beck L, Huq A, Wood B, Fuchs G, Faruque AS, et al.
2000. Climate and infectious disease: use of remote sensing
for detection of Vibrio cholerae by indirect measurement.
Proc Natl Acad Sci USA 97:1438–1443.
Loutan L, Bierens de Haan D, Subilia L. 1997. The health of asy-
lum seekers: from communicable disease screening to
post-traumatic disorders [in French]. Bull Soc Pathol Exot
90:233–237.
Madsen H, Bloch P, Phiri H, Kristensen TK, Furu P. 2001. Bulinus
nyassanus is an intermediate host for Schistosoma haema-
tobium in Lake Malawi. Ann Trop Med Parasitol 95:353–360.
Marques AC. 1987. Human migration and the spread of malaria
in Brazil. Parasitol Today 3:166–170.
MEA (Millennium Ecosystem Assessment). 2003. Ecosystem
and Human Well-being: A Framework for Assessment.
Washington, DC:Island Press.
Millennium Assessment Working Groups. 2004. Millennium
Ecosystem Assessment: Strengthening Capacity to
Manage Ecosystems Sustainably for Human Well-being.
Washington, DC:Meridian Institute. Available: http://www.
millenniumassessment.org [accessed 3 May 2004].
Ostfeld SR, Keesing F. 2000. Biodiversity and disease risk: the
case of Lyme disease. Conserv Biol 14:722–728.
Patz JA. 2002. A human disease indicator for the effects of
recent global climate change. Proc Natl Acad Sci USA
99:12506–12508.
Patz JA, Graczyk TK, Geller N, Vittor AY. 2000. Effects of envi-
ronmental change on emerging parasitic diseases. Int J
Parasitol 30:1395–1405.
Population Reference Bureau. 1998. 1998 World Population
Data Sheet. Washington, DC:Population Reference Bureau.
Rodo X, Pascual M, Fuchs G, Faruque AS. 2002. ENSO and
cholera: a nonstationary link related to climate change?
Proc Natl Acad Sci USA 99:12901–12906.
Rolland RM, Hausfater G, Marshall B, Levy SB. 1985. Antibiotic-
resistant bacteria in wild primates: increased prevalence in
baboons feeding on human refuse. Appl Environ Microbiol
49:791–794.
Rose JB, Epstein PR, Lipp EK, Sherman BH, Bernard SM, Patz JA.
2001. Climate variability and change in the United States:
potential impacts on water- and foodborne diseases
caused by microbiologic agents. Environ Health Perspect
109(suppl 2):211–221.
Schmidt KA, Ostfeld RS. 2001. Biodiversity and the dilution
effect in disease ecology. Ecology 82:609–619.
Silbergeld EK, Nash D, Trevant C, Strickland GT, de Souza JM,
da Silva RS. 2002. Mercury exposure and malaria preva-
lence among gold miners in Para, Brazil. Rev Soc Bras
Med Trop 35:421–429.
Singh J, Jain DC, Bhatia R, Ichhpujani RL, Harit AK, Panda RC,
et al. 2001. Epidemiological characteristics of rabies in Delhi
and surrounding areas, 1998. Indian Pediatr 38:1354–1360.
Straube E, Straube W, Kruger E, Bradatsch M, Jacob-Meisel M,
Rose HJ. 1999. Disruption of male sex hormones with
regard to pesticides: pathophysiological and regulatory
aspects. Toxicol Lett 107:225–231.
Tabor GM. 2002. Defining conservation medicine. In: Conservation
Medicine: Ecological Health in Practice (Aguirre AA, Ostfeld
RS, Tabor GM, House CA, Pearl MC, eds). New York:Oxford
University Press, 8–16.
Tadei WP, Thatcher BD, Santos JM, Scarpassa VM, Rodrigues IB,
Rafael MS. 1998. Ecologic observations on anopheline vec-
tors of malaria in the Brazilian Amazon. Am J Trop Med Hyg
59:325–335.
Taylor LH, Latham SM, Woolhouse ME. 2001. Risk factors for
human disease emergence. Philos Trans R Soc Lond B Biol
Sci 356:983–989.
Thompson DF, Malone JB, Harb M, Faris R, Huh OK, Buck AA,
et al. 1996. Bancroftian filariasis distribution and diurnal
temperature differences in the southern Nile delta. Emerg
Infect Dis 2:234–235.
Toole MJ, Waldman RJ. 1997. The public health aspects of
complex emergencies and refugee situations. Annu Rev
Public Health 18:283–312.
Veiga MM, Meech JA, Onate N. 1994. Mercury pollution from
deforestation [Letter]. Nature 368:816–817.
Wallis J, Lee DR. 1999. Primate conservation: the prevention of
disease transmission. Int J Primatol 20:803–826.
Weigle KA, Santrich C, Martinez F, Valderrama L, Saravia NG.
1993. Epidemiology of cutaneous leishmaniasis in
Colombia: environmental and behavioral risk factors for
infection, clinical manifestations, and pathogenicity.
J Infect Dis 168:709–714.
WHO. 1997. Health and Environment in Sustainable Development:
5 Years after the Earth Summit. Geneva:World Health
Organization. Available: http://www.who.int/archives/
inf-pr-1997/en/pr97-47.html [accessed 11 October 2003].
Wolfe ND, Eitel MN, Gockowski J, Muchaal PK, Nolte C,
Prosser AT, et al. 2000. Deforestation, hunting and the
ecology of microbial emergence. Global Change Hum
Health 1:10–25.
Wolfe ND, Switzer WM, Carr JK, Bhullar VB, Shanmugam V,
Tamoufe U, et al. 2004. Naturally acquired simian
retrovirus infections in central African hunters. Lancet
363(9413):932–937.
... The interaction between the host, the host microbiome, the pathogen, and the environment is called a four-way interaction, and it is complex, and it explains the emergence of pathogens and predicts the epidemic risks due to anthropogenic actions ( Figure 2) [59]. Anthropogenic actions, for example, drive the increasing rate of wildlife-human contact and the human-driven introductions of pathogens by providing conditions that promote our interaction with wild animal populations due to fundamental changes in the environment [60][61][62][63][64][65][66]. These impacts are not restricted to the emergence of zoonotic viruses, however, anthropogenic pollutants have been linked to several chronic diseases such as Parkinson's disease and diabetes [67][68][69][70]. ...
... Therefore, this set of environmental changes favors the interaction of pathogen agents with their vector, and with wild and domestic hosts, in addition to humans [76]. Consequently, there can be serious implications for environmental dynamics, such as the disappearance of species that Anthropogenic actions, for example, drive the increasing rate of wildlife-human contact and the human-driven introductions of pathogens by providing conditions that promote our interaction with wild animal populations due to fundamental changes in the environment [60][61][62][63][64][65][66]. These impacts are not restricted to the emergence of zoonotic viruses, however, anthropogenic pollutants have been linked to several chronic diseases such as Parkinson's disease and diabetes [67][68][69][70]. ...
Full-text available
Article
Population growth and industrialization have led to a race for greater food and supply productivity. As a result, the occupation and population of forest areas, contact with wildlife and their respective parasites and vectors, the trafficking and consumption of wildlife, the pollution of water sources, and the accumulation of waste occur more frequently. Concurrently, the agricultural and livestock production for human consumption has accelerated, often in a disorderly way, leading to the deforestation of areas that are essential for the planet’s climatic and ecological balance. The effects of human actions on other ecosystems such as the marine ecosystem cause equally serious damage, such as the pollution of this habitat, and the reduction of the supply of fish and other animals, causing the coastal population to move to the continent. The sum of these factors leads to an increase in the demands such as housing, basic sanitation, and medical assistance, making these populations underserved and vulnerable to the effects of global warming and to the emergence of emerging and re-emerging diseases. In this article, we discuss the anthropic actions such as climate changes, urbanization, deforestation, the trafficking and eating of wild animals, as well as unsustainable agricultural intensification which are drivers for emerging and re-emerging of zoonotic pathogens such as viral (Ebola virus, hantaviruses, Hendravirus, Nipah virus, rabies, and severe acute respiratory syndrome coronavirus disease-2), bacterial (leptospirosis, Lyme borreliosis, and tuberculosis), parasitic (leishmaniasis) and fungal pathogens, which pose a substantial threat to the global community. Finally, we shed light on the urgent demand for the implementation of the One Health concept as a collaborative global approach to raise awareness and educate people about the science behind and the battle against zoonotic pathogens to mitigate the threat for both humans and animals.
... Due to the accelerated impacts of global change, many ecosystems are facing a series of problems such as species extinction, biological invasion, pest outbreaks, and disease transmission (Patz et al., 2004;Pimm et al., 2014;Haddad et al., 2015), which is largely driven by the decrease in biodiversity and stability of ecosystems (Hooper et al., 2005;Dirzo et al., 2014). The relationship between diversity and stability is a focus of community ecology (Tilman and Downing, 1994;Rooney and Mccann, 2012), which has been debated in ecology for several decades, both theoretically and empirically (May, 1972;Thebault and Fontaine, 2010;Downing et al., 2020). ...
... Previous studies suggest that more pests or diseases often outbreak in monoculture forests or human-disturbed forests (Patz et al., 2004;Dirzo et al., 2014). We found rodent populations fluctuated more noticeably in younger stands than in older stands, which often imposed heavy damage on seed regeneration or reforestation projects, and provide strong evidence that a disturbing system with poor diversity is less stable and prone to pest or disease outbreaks. ...
Full-text available
Article
The relationship between diversity and stability is a focus in community ecology, but the relevant hypotheses have not been rigorously tested at trophic and network levels due to a lack of long-term data of species interactions. Here, by using seed tagging and infrared camera tracking methods, we qualified the seed-rodent interactions, and analyzed the associations of rodent community stability with species diversity, species abundance, and seed-rodent network complexity of 15 patches in a subtropical forest from 2013 to 2021. A total of 47,400 seeds were released, 1,467 rodents were marked, and 110 seed-rodent networks were reconstructed to estimate species richness, species abundance, and seed-rodent network metrics. We found, from younger to older stands, species richness and abundance (biomass) of seeds increased, while those of rodents decreased, leading to a seed-rodent network with higher nestedness, linkage density, and generality in older stands, but higher connectance in younger stands. With the increase of temperature and precipitation, seed abundance (biomass), rodent abundance, and the growth rate of rodent abundance increased significantly. We found rodent community stability (i.e., the inverse of rodent abundance variability) was significantly and positively associated with seed diversity, seed availability, linkage density and generality of seed-rodent networks, providing evidence of supporting the Bottom-Up Diversity-Stability Hypotheses and the Abundant Food Diversity-Stability Hypothesis. Our findings highlight the significant role of resource diversity and availability in promoting consumers' community stability at trophic and network levels, and the necessity of protecting biodiversity for increasing ecosystem stability under human disturbance and climate variation. (2022) High seed diversity and availability increase rodent community stability under human disturbance and climate variation.
... The interaction between the host, the host microbiome, the pathogen, and the environment is called a four-way interaction, and it is complex, and it explains the emergence of pathogens and predicts the epidemic risks due to anthropogenic actions ( Figure 2) [59]. Anthropogenic actions, for example, drive the increasing rate of wildlife-human contact and the human-driven introductions of pathogens by providing conditions that promote our interaction with wild animal populations due to fundamental changes in the environment [60][61][62][63][64][65][66]. These impacts are not restricted to the emergence of zoonotic viruses, however, anthropogenic pollutants have been linked to several chronic diseases such as Parkinson's disease and diabetes [67][68][69][70]. ...
... Therefore, this set of environmental changes favors the interaction of pathogen agents with their vector, and with wild and domestic hosts, in addition to humans [76]. Consequently, there can be serious implications for environmental dynamics, such as the disappearance of species that Anthropogenic actions, for example, drive the increasing rate of wildlife-human contact and the human-driven introductions of pathogens by providing conditions that promote our interaction with wild animal populations due to fundamental changes in the environment [60][61][62][63][64][65][66]. These impacts are not restricted to the emergence of zoonotic viruses, however, anthropogenic pollutants have been linked to several chronic diseases such as Parkinson's disease and diabetes [67][68][69][70]. ...
Full-text available
Article
Population growth and industrialization have led to a race for greater food and supplyproductivity. As a result, the occupation and population of forest areas, contact with wildlife andtheir respective parasites and vectors, the trafficking and consumption of wildlife, the pollution ofwater sources, and the accumulation of waste occur more frequently. Concurrently, the agriculturaland livestock production for human consumption has accelerated, often in a disorderly way, leadingto the deforestation of areas that are essential for the planet’s climatic and ecological balance. Theeffects of human actions on other ecosystems such as the marine ecosystem cause equally seriousdamage, such as the pollution of this habitat, and the reduction of the supply of fish and otheranimals, causing the coastal population to move to the continent. The sum of these factors leadsto an increase in the demands such as housing, basic sanitation, and medical assistance, makingthese populations underserved and vulnerable to the effects of global warming and to the emergenceof emerging and re-emerging diseases. In this article, we discuss the anthropic actions such asclimate changes, urbanization, deforestation, the trafficking and eating of wild animals, as well asunsustainable agricultural intensification which are drivers for emerging and re-emerging of zoonoticpathogens such as viral (Ebola virus, hantaviruses, Hendravirus, Nipah virus, rabies, and severeacute respiratory syndrome coronavirus disease-2), bacterial (leptospirosis, Lyme borreliosis, andtuberculosis), parasitic (leishmaniasis) and fungal pathogens, which pose a substantial threat to theglobal community. Finally, we shed light on the urgent demand for the implementation of the OneHealth concept as a collaborative global approach to raise awareness and educate people about thescience behind and the battle against zoonotic pathogens to mitigate the threat for both humansand animals.
... Mudanças no uso e ocupação do solo induzidas pelo Homem são as causas primárias de uma gama de surtos e emergência de doenças infecciosas, bem como de alterações nos mecanismos de transmissão de doenças endêmicas. O uso e ocupação do solo causam alterações no ambiente, e estas por sua vez iniciam uma cascata de fatores que exacerbam a emergência de doenças infecciosas (PATZ et al., 2004). O ambiente tem uma relação importante com a saúde da população. ...
Article
O objetivo do estudo foi identificar os aspectos da epidemiologia da Síndrome Pulmonar por Hantavírus (SPH) no Estado de Minas Gerais, Brasil, e sua relação com uso e ocupação do solo. Utilizaram-se dados de casos notificados e confirmados de SPH registrados no SINAN (Sistema de Informação de Agravo de Notificação) no período de 2002 a 2009. Nesse período ocorreram 209 casos de hantavirose, com média anual de 28 casos/ano. Maior número de casos (40) em 2005. As taxas de incidência e letalidade variaram 7,63 a 20,79/10.000.000 habitantes e 20% a 52%, respectivamente. Os casos concentraram-se nas macrorregiões do Triângulo Mineiro e Alto Paranaíba. Homens, da raça branca, na faixa etária de 21 a 40 anos, com 4 a 7 anos de estudo foram os mais acometidos. O local provável de infecção (LPI) mais frequente foi a zona rural (62,68%). Houve maior concentração em áreas de cerrado, com correlação positiva forte com culturas de feijão (Região Sul/Sudoeste) e soja no Triângulo Mineiro. Este estudo constitui a base para estudos de modelação mais complexos para quantificar e prever a importância dos fatores ambientais sobre a distribuição espacial do hantavírus neste estado.
... The dominance, shape, and connectivity of the landscape affect environmental health risks and sustainable urban development. For example, the higher the LSI, the higher the risk of infectious diseases [64,65]. Better landscape connectivity means higher species richness [66]. ...
Full-text available
Article
The ecological restoration of territorial space emphasizes the synergy between ecology and social development. On this basis, we used landscape index analysis methods to explore the spatiotemporal evolution of landscape patterns in urban areas on a district scale. Then, we used multiple regression analysis to explore the driving factors behind this evolution. The results showed the following: (1) Landscape compositions have changed significantly. The growth rate of construction land in the main districts was about three times that in the urban area. (2) There were differences in the characteristics of landscape pattern evolution. Arable land is becoming more fragmented as construction land expands outward. The shapes of public green spaces, arable land, and woodlands tend to be simple and regular. The degree of both urban sprawl and agglomeration decreased in the urban area and the main districts. Meanwhile, landscape separation first decreased and then increased, and landscape diversity increased. (3) Population growth, industrial development, changes in industrial structure, and real estate development are the main driving factors of landscape pattern evolution. Based on this, this study puts forward some suggestions for landscape pattern optimization, which is significant for ecological restoration planning and promotion.
Full-text available
Preprint
Background: The recent geographic expansion of Leishmania infantum vectors in the triple border area of Argentina, Brazil, and Paraguay has highlighted the need to know the seasonality, parasite infection rate, and the factors that contribute the dispersal and handling of this parasite. Methods: Entomological, quantitative longitudinal studies were conducted in Foz do Iguaçu, Brazil, where sand fly abundance was higher in cross-sectional studies. Monthly sand fly samplings occurred in 2014-2015. LeishmaniaDNA was detected by PCR and subsequently sequenced, classified, and the infection rate was estimated. The study also featured an observational and descriptive design. Environmental variables were analyzed at the micro- and mesoscales, and the data were evaluated along with entomological and infection inputs. Results: A total of 3,582 sand flies were caught. Lutzomyia longipalpiswas the predominant species (71.5%) among 13 species found in one year of sampling. Four species, Evandromyia edwardsi, Expapillata firmatoi, Micropygomyia ferreirana, and Pintomyia christenseni were reported for the first time. The NDVI, distance from water, sex, west-to-east wind, and wind speed were significant variables for the intra-environment presence and/or abundance of vectors. The presence and/or abundance of vectors in peri-domicile were influenced by rain, altitude, maximum temperature, minimum and maximum relative humidity, west-to-east wind, wind speed, and sex. Considering PCR positivity, females infected with L. infantum were found throughout the year, and especially with Lu. longipalpis (prevalence means of 16.4). Conclusions: Vector colonization concentrates on urban and peri-urban hotspot areas, with some individuals being present in various parts of the city and few sites showing high vector abundance. This distribution suggests that the risk of actual contact between humans and parasitic vectors in urban areas during the epidemic period is associated with patches of peri-urban vegetation and then spreads across urban areas. We can state that, in the period of this study, the most critical transmission phase for L. infantum in the region is from January to May. Therefore, future management plants to reduce access to reservoirs might reduce sand fly infection and consequently human and animal infections.
Article
Phlebotomines (Diptera: Psychodidae) are vectors of protozoa of the genus Leishmania and distributed throughout Brazil, formerly restricted to rural areas, have expanded including to periurban and urban regions, been recorded in different habitats. This study aimed to understand the dynamics of sand flies in different ecotopes in the municipality of Pains. Sand flies were captured during thirty samplings using HP light traps installed in seven different ecotopes for two consecutive nights, once a month, from August 2018 to July 2019. A total of 1,352 sand flies were captured, representing 24 species belong to ten genera. Evandromyia edwardsi was the most abundant species, followed by Evandromyia lenti and Micropygomyia quinquefer. Leishmania DNA was detected in seven female sand flies in four ecotopes, for an infection rate of 0.9%. Sand flies were collected in all seven ecotopes, although forest (23.04%), cave (20.88%) and pasture (17.75%) had higher abundance and richness. Similarity was found among ecotopes, indicating that they are all important for the maintenance of the sand fly community. Spatial analysis indicated high densities of sand flies in areas with natural characteristics. All ecotopes in the municipality were evidenced to have an adequate and harmonious epidemiological profile for the transmission and expansion of leishmaniasis throughout the territory. Because of the increasing environmental changes and deforestation in the municipality, the risk of generating ecological imbalance and increased cases of leishmaniasis is imminent, which highlights the importance of developing preventive and control strategies.
Article
The Colobines are a group of Afroeurasian monkeys that exhibit extraordinary behavioural and ecological diversity. With long tails and diverse colourations, they are medium-sized primates, mostly arboreal, that are found in many different habitats, from rain forests and mountain forests to mangroves and savannah. Over the last two decades, our understanding of this group of primates has increased dramatically. This volume presents a comprehensive overview of the current research on colobine populations, including the range of biological, ecological, behavioural and societal traits they exhibit. It highlights areas where our knowledge is still lacking, and outlines the current conservation status of colobine populations, exploring the threats to their survival. Bringing together international experts, this volume will aid future conservation efforts and encourage further empirical studies. It will be of interest to researchers and graduate students in primatology, biological anthropology and conservation science. Additional online resources can be found at www.cambridge.org/colobines.
Article
Land conversion and the resulting contact between domesticated and wild species has arguably been the single largest contributor to the emergence of novel epizootic and zoonotic diseases in the past century. An unintended consequence of these interactions is zoonotic or epizootic disease spillovers from wild species to humans and their domesticates. Disease spillovers are edge effects of land conversion and are sensitive to the size and shape of converted areas. We combine spatial metrics from landscape ecology with theoretical epidemiological models to understand how the size and shape of land conversion affect epizootic and zoonotic disease transmission of single and two species populations. We show that the less compact the converted area, and the greater the depth of the contact zone, the more rapidly will an introduced disease spread through the domesticated population.
Full-text available
Thesis
Infectious diseases are an increasing threat to biodiversity and human health. Therefore, developing a general understanding of the drivers shaping host-pathogen dynamics is of key importance in both ecological and epidemiological research. Disease dynamics are driven by a variety of interacting processes such as individual host behaviour, spatiotemporal resource availability or pathogen traits like virulence and transmission. External drivers such as global change may modify the system conditions and, thus, the disease dynamics. Despite their importance, many of these drivers are often simplified and aggregated in epidemiological models and the interactions among multiple drivers are neglected. In my thesis, I investigate disease dynamics using a mechanistic approach that includes both bottom-up effects - from landscape dynamics to individual movement behaviour - as well as top-down effects - from pathogen virulence on host density and contact rates. To this end, I extended an established spatially explicit individual-based model that simulates epidemiological and ecological processes stochastically, to incorporate a dynamic resource landscape that can be shifted away from the timing of host population-dynamics (chapter 2). I also added the evolution of pathogen virulence along a theoretical virulence-transmission trade-off (chapter 3). In chapter 2, I focus on bottom-up effects, specifically how a temporal shift of resource availability away from the timing of biological events of host-species - as expected under global change - scales up to host-pathogen interactions and disease dynamics. My results show that the formation of temporary disease hotspots in combination with directed individual movement acted as key drivers for pathogen persistence even under highly unfavourable conditions for the host. Even with drivers like global change further increasing the likelihood of unfavourable interactions between host species and their environment, pathogens can continue to persist with heir hosts. In chapter 3, I demonstrate that the top-down effect caused by pathogen-associated mortality on its host population can be mitigated by selection for lower virulent pathogen strains when host densities are reduced through mismatches between seasonal resource availability and host life-history events. I chapter 4, I combined parts of both theoretical models into a new model that includes individual host movement decisions and the evolution of pathogenic virulence to simulate pathogen outbreaks in realistic landscapes. I was able to match simulated patterns of pathogen spread to observed patterns from long-term outbreak data of classical swine fever in wild boar in Northern Germany. The observed disease course was best explained by a simulated high virulent strain, whereas sampling schemes and vaccination campaigns could explain differences in the age-distribution of infected hosts. My model helps to understand and disentangle how the combination of individual decision making and evolution of virulence can act as important drivers of pathogen spread and persistence. As I show across the chapters of this thesis, the interplay of both bottom-up and top-down processes is a key driver of disease dynamics in spatially structured host populations, as they ultimately shape host densities and contact rates among moving individuals. My findings are an important step towards a paradigm shift in disease ecology away from simplified assumptions towards the inclusion of mechanisms, such as complex multi-trophic interactions, and their feedbacks on pathogen spread and disease persistence. The mechanisms presented here should be at the core of realistic predictive and preventive epidemiological models.
Full-text available
Article
At Cape Maclear on the Nankumba Peninsula, close to the southern end of Lake Malawi, Schistosoma haematobium is highly prevalent in the local people and many tourists become infected with this parasite each year. A ‘Bilharzia Control Programme’ was initiated in this area in August 1998, as a development collaboration between the Government of Malawi, the Danish Agency for Development Assistance (Danida), and the Danish Bilharziasis Laboratory. Although Bulinus globosus is a known host for S. haematobium, B. nyassanus has not previously been incriminated as an intermediate host. However, schistosome-infected B. nyassanus were discovered in surveys to identify transmission sites on the peninsula. Experimental infections of wild-caught B. nyassanus with S. haematobium proved successful and S. haematobium eggs were found in hamsters experimentally exposed to cercariae retrieved from schistosome-infected, field-collected B. nyassanus. These are remarkable observations since, although there are very few reports of diploid members of this species group being experimentally infected with S. haematobium, B. nyassanus is a diploid member (2n = 36) of the truncatus/tropicus group. Bulinus nyassanus is probably responsible for transmission in Lake Malawi, along rather exposed shorelines, devoid of aquatic macrophytes, with a substrate of sand or gravel.
Full-text available
Article
Utilitarian arguments concerning the value of biodiversity often include the benefits of animals, plants, and microbes as sources of medicines and as laboratory models of disease. The concept that species diversity per se may influence risk of exposure to disease has not been well developed, however. We present a conceptual model of how high species richness and evenness in communities of terrestrial vertebrates may reduce risk of exposure to Lyme disease, a spirochetal ( Borrelia burgdorferi) disease transmitted by ixodid tick vectors. Many ticks never become infected because some hosts are highly inefficient at transmitting spirochete infections to feeding ticks. In North America, the most competent reservoir host for the Lyme disease agent is the white-footed mouse ( Peromyscus leucopus), a species that is widespread and locally abundant. We suggest that increases in species diversity within host communities may dilute the power of white-footed mice to infect ticks by causing more ticks to feed on inefficient disease reservoirs. High species diversity therefore is expected to result in lower prevalence of infection in ticks and consequently in lower risk of human exposure to Lyme disease. Analyses of states and multistate regions along the east coast of the United States demonstrated significant negative correlations between species richness of terrestrial small mammals (orders Rodentia, Insectivora, and Lagomorpha), a key group of hosts for ticks, and per capita numbers of reported Lyme disease cases, which supports our “dilution effect” hypothesis. We contrasted these findings to what might be expected when vectors acquire disease agents efficiently from many hosts, in which case infection prevalence of ticks may increase with increasing diversity hosts. A positive correlation between per capita Lyme disease cases and species richness of ground-dwelling birds supported this hypothesis, which we call the “rescue effect.” The reservoir competence of hosts within vertebrate communities and the degree of specialization by ticks on particular hosts will strongly influence the relationship between species diversity and the risk of exposure to the many vector-borne diseases that plague humans. Resumen: Argumentos utilitarios relacionados con el valor de la biodiversidad frecuentemente incluyen los beneficios de animales, plantas y microbios como recursos para medicinas y como modelos de enfermedades en laboratorio. Sin embargo, la idea de que la diversidad de especies por sí misma puede influenciar el riesgo de exposición a enfermedades no ha sido bien desarrollada. Presentamos un modelo conceptual de cómo la riqueza de especies y la uniformidad en comunidades de vertebrados terrestres puede reducir el riesgo de exposición a la enfermedad de Lyme, una enfermedad causada por una espiroqueta ( Borrelia burgdorferi) y transmitida por una garrapata ixódida. Muchas garrapatas nunca son infectadas debido a que los huéspedes son altamente ineficientes en la transmisión de espiroquetas a las garrapatas que se alimentan de ellos. En Norte América, el huésped reservorio más competente del agente de la enfermedad de Lyme es el ratón de patas blancas ( Peromyscus leucopus), una especie de amplia dispersión y localmente abundante. Sugerimos que los incrementos en la diversidad de especies dentro de las comunidades de huéspedes pueden diluir el potencial de infección de las garrapatas por el ratón de patas blancas al ocasionar que más garrapatas se alimenten de reservorios ineficientes en la transmisión de la enfermedad. Por lo tanto, se esperaría que una alta diversidad de especies resulte en una prevalencia de infección de garrapatas reducida y, por lo tanto, en una disminución del riesgo de exposición de humanos a la enfermedad de Lyme. Un análisis por estado y de varios estados a lo largo de la costa este de los Estados Unidos demostró correlaciones significativamente negativas entre la riqueza de especies de mamíferos terrestres pequeños (órdenes Rodentia, Insectivora, y Lagomorfa), un grupo clave de huéspedes para garrapatas, y los números per capita de casos de la enfermedad de Lyme reportados, lo cual apoya nuestra hipótesis de efecto de dilución. Contrastamos estos resultados con lo que se podría esperar cuando los vectores adquieren eficientemente agentes de la enfermedad de muchos huéspedes, caso en el cual, una alta diversidad causaría la prevalencia de infección de garrapatas permaneciendo alta aún cuando la diversidad de huéspedes disminuyera. Una correlación positiva entre los casos de la enfermedad de Lyme per capita y la riqueza de especies de aves residentes del suelo apoya esta hipótesis, que hemos llamado efecto de rescate. La capacidad de reservorio de huéspedes dentro de las comunidades de vertebrados y el grado de especialización de las garrapatas en huéspedes particulares, influenciaría fuertemente la relación entre la diversidad de especies y el riesgo de exposición a muchas de las enfermedades transmitidas por vectores que infectan a humanos.
Full-text available
Article
Many infectious diseases of humans are caused by pathogens that reside in nonhuman animal reservoirs and are transmitted to humans via the bite of an arthropod vector. Most vectors feed from a variety of host species that differ dramatically in their reservoir competence; that is, their probability of transmitting the infection from host to vector. We explore a conceptual model of what we termed the "dilution effect," whereby the presence of vertebrate hosts with a low capacity to infect feeding vectors (incompetent reservoirs) dilute the effect of highly competent reservoirs, thus reducing disease risk. Using Lyme disease as an example, we demonstrate the presence and estimate the magnitude of the dilution effect for local sites in eastern New York State. We found that the prevalence of Lyme disease spirochetes, Borrelia burgdorferi, in field-collected Ixodes ticks (37.6% and 70.5% for nymphal and adult stages, respectively) was dramatically lower than expected, (∼90% and >95% for nymphal and adult stages, respectively) if ticks fed predominantly on highly competent reservoirs, white-footed mice (Peromyscus leucopus) and eastern chipmunks (Tamias striatus). We inferred the role of additional host species using an empirically based model that incorporated data on tick burdens per host, relative population densities of hosts, and reservoir competence of each host. Assuming an empirically realistic reservoir competence of 5% for non-mouse and non-chipmunk hosts, we determined that alternative hosts must provide 61% and 72% of larval and nymphal meals, respectively. Using computer simulations, we assembled simulated host communities that differed in species richness, evenness, and net interactions between alternative hosts and mice. We found that increasing species richness (but not evenness) reduced disease risk. Effects were most pronounced when the most competent disease reservoirs were community dominants and when alternative hosts had a net negative influence on the dominance of mice as a host for ticks. Our results highlight a critical role of biodiversity and host community ecology in the transmission of vector-borne zoonotic diseases that in turn has important consequences for human health.
Full-text available
Article
Understanding how novel microbes enter into the human population is perhaps the fundamental goal of the study of emerging infectious diseases (EID). The frequency at which microbes will emerge is determined by the diversity of microbes present in the environment, the level of contact between a potential host and this microbial diversity and the susceptibility of the novel host to infection. While a range of microbial media exist, including soils, plants and animals, the greatest emergence risks come through contact with media, such as wild vertebrates, that share susceptibility characteristics with humans and live in regions of high microbial diversity. Lowland tropical forests provide a rich environment for emergence due to their combination of high vertebrate and microbial biodiversity. Human activities that occur in lowland tropical forests, such as ecotourism, logging, and the hunting of wild vertebrates have the potential to increase the frequency of microbial emergence. Of these and other activities considered, hunting and the processing of bushmeat, particularly from nonhuman primates, involve the greatest level of risk for the transmission of microbes. While human hunting in lowland tropical forests poses a serious threat for microbial emergence, it is by no means alone among contemporary human behaviors in doing so, sharing risk characteristics with activities as diverse as lab microbiology, wildlife veterinary work, and modern food production practices.
Article
Evidence of simian immunodeficiency virus (SIV) infection has been reported for 26 different species of African nonhuman primates. Two of these viruses, SIVcpz from chimpanzees and SIVsm from sooty mangabeys, are the cause of acquired immunodeficiency syndrome (AIDS) in humans. Together, they have been transmitted to humans on at least seven occasions. The implications of human infection by a diverse set of SIVs and of exposure to a plethora of additional human immunodeficiency virus–related viruses are discussed.
Article
The American Water System has conducted extensive monitoring of its operations since 1988. Analysis of 347 surface water samples collected between 1988 and 1993 showed that the prevalence rate of Giardia and Cryptosporidium was 53.9 percent and 60.2 percent, respectively. But because the parasite assay does not indicate viability or virulence, these results do not necessarily indicate that these water systems, were at risk from waterborne pathogens. To supplement coagulation and filtration, the average system will have to apply sufficient disinfection to reduce viable Giardia levels by 3.1 log₁₀. An analysis of existing disinfection practices shows that most systems are already applying disinfectant at a level sufficient to reduce Giardia levels. However, the proposed Disinfectants/Disinfection By-products (D/DBP) Rule may hamper the ability of water utilities to apply sufficient disinfection under current operating conditions. Careful integration of the D/DBP and the Enhanced Surface Water Treatment rule is encouraged.