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Links between ecological integrity, emerging
infectious diseases originating from wildlife, and
other aspects of human health - an overview of
the literature
Tom Evans, Sarah Olson, James Watson, Kim Gruetzmacher, Mathieu Pruvot, Stacy Jupiter,
Stephanie Wang, Tom Clements and Katie Jung
April 2020
OUR MISSION
The Wildlife Conservation Society saves wildlife
and wild places worldwide through science,
conservation action, education, and
inspiring people to value nature.
https://wcs.org
OUR VISION
WCS envisions a world where wildlife
thrives in healthy lands and seas, valued
by societies that embrace and benefit
from the diversity and integrity of life on earth.
CONTENTS
Summary 1
Introduction 2
Review of the Evidence 3
Point 1. Degradation has significantly altered ecological systems 3
Point 2. The majority of emerging infectious disease threats are
zoonotic, originate from wildlife, and often have major social and
economic impacts 4
Point 3. Ecological degradation increases the overall risk of zoonotic
disease outbreaks originating from wildlife 5
Point 4. Degradation of ecosystems also has complex effects, often
negative, on many other aspects of human health 8
Solutions and responses 9
References 12
Contacts:
Tom Evans, Lead, REDD+ and Forest Conservation Program,
tevans@wcs.og;
Sarah Olson,
Associate Director of Epidemiology,
solson@wcs.org
;
James Watson, Director, Science and Research Initiative,
jwatson@wcs.org
1
SUMMARY
As a result of the COVID-19 pandemic, there is heightened public interest in the risk factors that
lead to such events. This report contains an overview of the literature linking declines in the
integrity of ecosystems to impacts on human health, in particular the risk of emerging infectious
disease outbreaks that originate in wildlife. The review identified four key findings, as follows.
1. Degradation has significantly altered ecological systems worldwide and continues to
expand into new areas.
2. The majority of emerging infectious disease
1
threats are zoonotic, originate from wildlife,
and often cause major social and economic impacts.
3. Ecological degradation increases the overall risk of zoonotic disease outbreaks
originating from wildlife.
a. This relationship has been shown for multiple individual diseases, in regional
and global studies and in theoretical models, although the proportion of cases of
degradation that lead to substantially increased risk is not well understood.
a. The increased risk results from multiple interacting pathways including increased
human contact with pathogens and disruption in pathogen ecology.
b. The key “ingredients” that accentuate the risk of an emerging infectious disease
spillover event are activities (e.g., creation of new habitat edges, wildlife trade and
consumption, agricultural intensification) in areas of high biodiversity that
elevate contact rates between humans and certain high-risk wildlife species.
4. Degradation of ecosystems also has complex effects, feedback loops, and some notable
negative impacts on many other aspects of human health, including: the prevalence of
long-established (endemic) zoonotic diseases, the prevalence of vector-borne and water-
borne diseases; air quality; nutrition; mental health; and access to traditional medicines;
as well as effects on human health through the impacts of climate change.
Hence, avoiding ecosystem degradation (by keeping ecosystems as intact as possible and
avoiding the creation of high-risk interface zones and high-risk activities that increase human-
wildlife contact), combined with broader One Health
2
approaches that address the full range of
risk factors, will help to reduce the risk to humanity from emerging zoonoses and can have other
beneficial health outcomes as well.
Protecting ecological integrity should be a priority action within any comprehensive plan to
avoid future zoonotic outbreaks, alongside other critical measures such as ending the
commercial wildlife trade for human consumption, closing commercial wildlife markets,
building surveillance and response systems, providing global access to health care, and
mitigating disease risks associated with domestic animals.
A One Health approach, optimizing human health and ecological integrity, can be used to find
solutions for different landscape contexts (e.g. remote intact landscapes, mixed, partly natural
landscapes, and heavily human-dominated landscapes).
1
‘Emerging infectious diseases can be defined as infections that have newly appeared in a population or have
existed but are rapidly increasing in incidence or geographic range’ (Morse 1995).
2
www.wcs.org/one-planet-one-health-one-future; www.onehealthglobal.net/what-is-one-health/
2
These conclusions are based on a range of evidence types including detailed case studies, global
analyses, modelling, and broad expert consensus.
Whilst the key conclusions are clear, it is important to acknowledge that the science is still
somewhat incomplete and it is difficult to make predictions at the scale of individual
ecosystems, locations or infectious agents, especially as outbreaks are inherently rare events and
the exact relationship between pathogen dynamics and ecosystem change is often context-
specific and subject to interactions with many other environmental, socio-economic, political
and cultural factors.
In addition to lowering disease spillover risk, avoiding environmental degradation has many
related benefits, including: climate change mitigation; climate change adaptation and
environmental resilience; maintenance of watersheds and rainfall patterns; biodiversity
conservation; and the protection of the homelands and livelihoods of Indigenous Peoples and
local communities.
INTRODUCTION
The devastating emergence of the virus causing COVID-19 has led to increased interest in the
factors that result in pandemics and other disease outbreaks. There is an extensive body of
literature on emerging infectious diseases that originate from wild animals, much of it built up
since the SARS epidemic of 2002-2004 raised global awareness of the topic. The wildlife trade
has been identified as one key risk factor and has rightly drawn a great deal of attention. This
review examines information relating to another commonly postulated risk factor - damage to
the integrity of ecosystems. It was developed to inform the institutional position WCS takes on
this topic, and the advice we share with our many partners around the world.
The review, whilst not intended to be a comprehensive or systematic review, considers a wide
sample of publications through to March 2020, with a focus on the peer-reviewed literature, and
draws on the combined expertise of scientific and policy staff from across WCS, including our
dedicated programs on wildlife health and on the conservation of intact forests.
In broad terms the integrity of an ecosystem is the degree of
naturalness
or, equivalently, degree
of absence of human modification. A widely used definition of ecosystem integrity is 'the ability
of an ecological system to support and maintain a community of organisms that has species
composition, diversity, and functional organization comparable to those of natural habitats
within a region (Parrish et al. 2003).
Damage to the integrity of ecosystems can take many forms, including deforestation,
fragmentation, construction of linear infrastructure, mining, extraction of oil or gas, pollution,
altered fire regimes, logging and the draining or flooding of natural habitats. As described
below, such changes often increase the likelihood that humans will be exposed to unfamiliar
and sometimes deadly micro-organisms. We do not review data on the wildlife trade in detail,
but it is closely linked to the issue of ecological integrity, because so much of the wildlife trade is
associated with areas where degradation is taking place, often enabled by increases in access to
newly fragmented or exploited frontier regions. Furthermore, the loss of wildlife populations
(‘defaunation’) is itself an important form of ecosystem degradation, disrupting many ecological
processes.
Beyond the health aspects discussed here, high ecological integrity is also important for a wide
range of other critical values and benefits to humanity, as reviewed recently by Watson et al.
(2018) for forests.
3
Julie Larsen Maher © WCS
REVIEW OF THE EVIDENCE
The following sections cover the four linked points set out in the summary.
Point 1. Degradation has significantly altered ecological systems
Humanity has been reshaping Earth’s ecosystems for millennia. We engage in large-scale
conversion of natural habitats to agricultural crops and urban areas to feed and house our
burgeoning population, and we change the state of natural systems through activities like
hunting, logging, resource extraction, infrastructure construction, recreation and fire
management. There has been a myriad of recent attempts to map the level of anthropogenic
environmental degradation across the land and ocean with some estimates showing that ~80%
of both realms have clear evidence of anthropogenic modification, varying in extent across
particular ecosystems (Venter et al., 2016; Jones et al. 2018).
The IPBES global synthesis report released in 2019 (IPBES 2019) clearly outlined the recorded
evidence of the multitude of impacts of human activity on ecological systems, including:
• significantly altered global patterns of species composition and abundance,
• loss and appropriation of primary productivity,
• changes in land-surface hydrology and albedo,
• alterations to the biogeochemical cycles of carbon, nitrogen, and phosphorus.
Many natural scientists argue that the anthropogenic degradation placed on ecosystems has
meant Earth has entered a human-dominated geological era termed the Anthropocene (Malhi et
al. 2014) and we are increasingly transgressing catastrophic environmental boundaries (Steffen
et al. 2015).
4
Point 2. The majority of emerging infectious disease threats are zoonotic, originate
from wildlife, and often have major social and economic impacts.
The World Organization for Animal Health (OIE) defines zoonotic diseases ‘as infectious
diseases that are naturally transmitted from vertebrate animals to humans and vice versa’ (Wang
and Crameri 2014). Emerging infectious diseases can be defined as infections that have newly
appeared in a population or have existed but are rapidly increasing in incidence or geographic
range (Morse 1995). An outbreak is the occurrence of one or more cases in a group of individuals
in a defined region. Spillover occurs when an animal pathogen successfully jumps to humans.
2a) The majority of emerging infectious disease threats are zoonotic
• More than 335 emerging infectious disease outbreaks (involving 183 distinct pathogens)
were reported worldwide during 1940-2004, more than 50/decade, and the rate of
outbreaks is increasing (Jones et al. 2008).
• In recent years, 52% of all emerging infectious disease events originated in wildlife.
Among emerging zoonoses specifically, 72% of outbreaks have originated in wildlife
(with the rest from domestic animals). The frequency of outbreaks originating in wildlife
is increasing. All facts under this bullet are from Jones et al. (2008).
• Populations of wild animals carry a high diversity of the types of infectious agents that
could potentially jump to humans, with higher diversity of such agents where the
diversity of host animals is higher (e.g. Anthony et al. 2017). Most diseases in wild
animals remain very poorly studied, many pathogens remain unidentified, and many
spillover events are overlooked (Johnson et al. 2020).
• The global connectivity of human society greatly increases the long-distance transport of
disease vectors (Tatem et al. 2006) and of animals infected with infectious pathogens
(Can et al. 2019), increasing the number of human-wildlife interfaces where pathogens
can spill over into humans. Connectivity also facilitates subsequent human-human
transmission.
• Less than 300 viruses from 25 high-risk viral families are known to infect people, yet
scientists have estimated there are around 1.7 million viruses from these same viral
families that are not yet discovered in mammals and birds, of which 700,000 are believed
to have zoonotic potential (Carroll et al. 2018).
2b) Economic and societal impacts of zoonotic diseases
• Zoonoses of domestic and wildlife origin combined are mostly long-established as
endemic threats. The 13 top ranked zoonotic diseases by scale of impact largely fall into
this category and annually they are estimated to be responsible for over 2 million deaths
and 2 billion illnesses (ILRI 2012).
• Emerging zoonoses have significant implications in terms of both public health and
economic stability, with the costs of many individual recent major outbreaks such as
SARS, MERS and Ebola reckoned in the tens of billions of US dollars and exceeding 1-2%
of GDP in less wealthy countries (GPMB 2019).
o The impact of the 2002-2004 SARS Coronavirus epidemic (774 deaths) on
tourism, food and travel in mainland China alone was estimated at US$8.5bn
(Beutels et al., 2009). The total global cost, associated with lost economic activity,
is estimated to have been around $40 billion (Knobler et al. 2004).
o The 2014 Ebola outbreak in West Africa cost an estimated US$2.2bn in GDP
alone and wiped out many of the recent development gains in Guinea, Liberia,
5
and Sierra Leone, which had been among the fastest growing economies in the
world (CDC, 2016; International Working Group On Financing Preparedness,
2017).
• The costs of a single severe future influenza pandemic, which are also indicative of the
potential costs of a pandemic originating from wildlife, were predicted to reach US$1.5
trillion or 3.1% of global GDP for one year at 2006 prices (Burns et al. 2006), whilst the
annualized cost to the global economy of occasional severe pandemics averaged over
long periods was estimated at $80-$500 bn/year (up to 0.6% of global GDP) depending
on whether or not deaths were ascribed an economic cost (Fan et al. 2018).
• Recent estimates suggest that the cost of the unfolding COVID-19 pandemic to the world
economy, in purely monetary terms, will be US$1-2 trillion, possibly more (UNCTAD
2020), with huge additional costs to human life and wellbeing.
Point 3. Ecological degradation increases the overall risk of zoonotic disease
outbreaks originating from wildlife
There are multiple interacting lines of evidence that support this conclusion, which is reflected
in numerous recent reviews of the topic (e.g. Patz et al. 2004, Karesh et al. 2012, Gottdenker et al.
2014, Murray et al. 2016, UNEP 2016, Watson et al. 2018, DiMarco et al. 2020). The issue is also
reflected in the recently issued ‘Berlin Principles on One Health’ white paper
3
.
The land-use changes
4
that tend to elevate disease risk include deforestation, forest degradation
(e.g. through logging), fragmentation, expansion of infrastructure (e.g. roads, railways,
powerlines, dams), changes in drainage, and hunting and capture for trade (Patz et al. 2004, Loh
et al. 2015). Risks are further multiplied by large movements of human populations, agricultural
intensification near to natural areas, and climate change, among other factors (Gebreyes et al.
2014, Karesh et al. 2012).
The main lines of evidence summarized below are (a) case studies, (b) global/regional analyses
and (c) theoretical modelling. They point to (d) a range of different pathways or mechanisms by
which the effects take place.
a)
Case studies
Multiple examples of zoonotic disease outbreaks from wildlife have been reported in the
literature as being associated with forest degradation, human encroachment on forests, and
wildlife trade chains that connect biodiverse forests to markets:
• SARS and COVID-19. The evolutionary host of the SARS virus (SARS-CoV) and the
closely-related COVID-19 virus (SARS-CoV-2) are bats and in both cases, index cases
were associated with wildlife markets. It is thought that SARS-CoV passed through civets
(wild or farmed) before infecting humans and it is unknown at this stage if SARS-CoV-2
also passed through an intermediate host (Hu et al. 2017; Lu et al. 2020; Li et al., 2006).
Here the main issue is the volume, mixing, unsanitary conditions, and overcrowding of
wildlife that brought a bat virus into contact with a variety of animals in wildlife trade
chains originating in natural habitats and ending at urban markets.
3
https://www.wcs.org/one-planet-one-health-one-future
4
Following the infectious disease literature, the term 'land-use change' is used here in a broad sense to include
both damage to ecosystems (often called degradation) and ecosystem cover loss (e.g. deforestation)
6
• Hendra virus. In Australia, science suggests declining eucalyptus habitat has altered
flying fox foraging behaviour and increased spillover risk of Hendra virus to humans
(Giles et al. 2018).
• Nipah virus in Malaysia. The emergence of Nipah virus in 1998 is linked to the ecology
of bats in changing landscapes. During this time period, Pteropid fruit bats experienced a
large reduction of flowering and fruiting trees as a result of slash and burn deforestation
and an ENSO-linked drought. This led to these bats ranging into cultivated fruit orchards
that adjoined pig farms which had recently expanded into forest-edge situations (Chua et
al. 2002).
• Nipah virus in Bangladesh. Case villages with Nipah virus spillovers had higher human
population density than control villages and more forest fragmentation than other parts
of the country. The number of bat roosts increased with fragmentation and was thought
to be associated with home gardens of diverse fruit trees that may provide a more
reliable food source than nearby intact forests (Hahn et al. 2014).
• Ebola. In Central Africa, an association was found between Ebola outbreaks and fine-
scale measures of forest fragmentation, consistent with suspected transmission pathways
from forest-dwelling bats to forest-edge human communities (Rulli et al. 2017,
Wilkinson 2018).
• HIV. Human viruses responsible for AIDS have resulted from at least four cross-species
spillovers of simian immunodeficiency viruses involving the Sooty mangabey,
chimpanzee, and western gorilla, all of which live in extensive forests. These lentiviruses
can penetrate mucous membranes so it is believed contact with ape bodily fluids
associated with the hunting, butchering and consumption of animals in trade led to the
spillovers. One of these transmission events, likely occurring between 1910 and 1930,
gave rise to the HIV strain behind pandemic AIDS (Sharp and Hahn, 2011).
• Malaria in Malaysia. In Malaysian Borneo the main vector is
Anopheles leucosphyrus
and the malaria parasite is
Plasmodium knowelsi
, which primarily infects macaques.
Since 2004 it appears deforestation has altered the dynamics of the entire system,
impacting vector habitats as well as abundance and distribution of macaques and
humans. Cleared land within 1 km and deforestation within 4-5 km of households
influenced vector abundance and high historical forest loss is correlated with higher
incidence of infections (Fornace et al. 2016; Brock et al. 2019).
• Lyme disease. In this system, home of the ‘dilution effect’, one reservoir host, the white-
footed mouse, is more competent at transmitting the bacteria that causes Lyme disease to
biting
Ixodes
ticks than other small-mammal hosts (which therefore provide a
dampening or ‘dilution’ effect). The larval and nymphal ticks feed non-selectively so
changes in host composition end up impacting human disease risk. In the presence of
fragmentation, the white-footed mice are more abundant for the larval and nymphal
ticks to feed on (and white-tailed deer are also more abundant for the adult ticks to feed
on). Hence when biodiversity is lost, resilient species like the mouse are more prevalent,
more ticks take more blood meals from the mice and subsequently have higher
prevalence of the bacteria that causes Lyme disease (Keesing et al. 2009, Turney et al.
2014).
b)
Global and regional analyses
There are few truly global-scale quantitative analyses of the relationship between emerging
infectious disease risk and land-use change, but those large-scale studies that do exist
support the conclusion that large-scale disturbance of ecosystems is associated with
increased risk of spillover events.
7
• During 1940-2004 34% of emerging zoonoses were believed to be associated primarily
with either land-use change or activities relating to bushmeat (Loh et al. 2015, UNEP
2016).
• Mapping outbreaks globally suggests that land-use change in tropical forest regions is
one of the key risk factors associated with disease spillovers from wildlife into humans
(Allen et al. 2017).
• Two regional multi-pathogen studies present strongly suggestive evidence that
biodiversity decline and loss of ecosystem integrity play a role in driving zoonotic
outbreaks, for the Asia-Pacific (Morand et al. 2014) and for Australia (McFarlane et al.
2013).
• The number of zoonotic diseases found in different wildlife species varies depending on
a number of factors, including some which relate to threats to the ecosystems that they
occupy. For example, more zoonotic diseases are found in threatened species facing
declines in their habitat, or high pressure from exploitation, compared to those
threatened for other reasons (Johnson et al. 2020).
Following biodiversity loss, abundant species with no extinction risk and increasing
populations (e.g. adaptable or ‘weedy’ species that thrive in heavily modified landscapes) are
also significant carriers of zoonoses, indicating that degradation of intact ecosystems is not
the only pathway to increasing the risk of wildlife-human transmission (Johnson et al. 2020,
Keesing 2010, Salkeld et al. 2013).
c)
Theoretical modelling
Several recent modelling studies provide theoretical support to the plausibility of increased
spillover risk being linked to ecosystem degradation (e.g. Myers et al 2013, Gortazar et al.
2014, Faust et al. 2018, Wilkinson et al. 2018, Borremans et al. 2019).
d)
Mechanisms
Across these various lines of evidence, several multiple interacting pathways are known or
suspected to lead to increased risk of disease transmission. These include:
• Increased contact between humans, livestock and pathogens along newly created edges
o These edges represent areas where newly arrived human and livestock
populations without immunity mix with unfamiliar pathogens, with contacts
sometimes further increased by the movement of host species in response to the
disrupted ecology of their habitat (Bloomfield et al. 2020, Brownstein et al. 2005,
Johnson et al. 2020, da Silva-Nunes et al. 2008). Fragmentation has placed over
70% of the world’s forests within 1 km of an edge (Haddad et al 2015) and is
worsening across the tropics (Taubert et al. 2018).
• Increased contact with humans along wildlife trade chains.
o Much wildlife trade originates from recently opened frontier areas where
populations have not yet been significantly depleted by over-harvest. There is
abundant evidence that large trade volumes, mixing of diverse species, and poor
hygiene practices expose people all along these trade chains to increased risk of
infection (Bloomfield et al. 2020, Greatorex et al. 2016, Pruvot et al. 2019).
• Changes to pathogen abundance due to changes in host abundance, diversity and
susceptibility.
o Degradation can cause increases in the local populations of host or vector species,
raising the chance of transmission. Habitat damage can also place individuals
under increased stress, making them more susceptible to infections (Levi et al.
8
2012, Civitello et al. 2015, Rulli et al. 2017, Olson et al. 2010, Vittor et al. 2006,
2009).
• Rapid evolution/mutation of pathogens due to novel conditions and novel hosts is also
suspected to be a contributory factor (Zohdy et al. 2019).
It is also possible that changes in the biodiversity within ecosystems (e.g. extinctions or local
extirpations of some species) can alter the likelihood of diseases being transmitted among the
remaining species (‘dilution’ and ‘amplification’ effects), although there is insufficient evidence
to confirm how common these alternative patterns are (Keesing et al. 2009, Randolph & Dobson
2012). It is well known for Lyme disease (see above) but has been looked for in other disease
systems (Hanta virus and West Nile virus) with mixed results (Suzan et al. 2009; Luis et al. 2018;
Tran et al. 2017; Koenig et al. 2010; Salkeld et al. 2013).
Point 4. Degradation of ecosystems also has complex effects, often negative, on many
other aspects of human health
Vector-borne and parasitic disease
There are several studies of the prevalence of non-zoonotic vector-borne disease in relation to
ecosystem change. Some show increases, others do not:
● Malaria
○
The Amazon
. Deforestation has altered mosquito ecology, resulting in more
larval breeding habitat and higher human biting rates of
Anopheles darlingi
,
which is a highly competent vector for the more deadly falciparum malaria. This
phenomenon is ephemeral and occurs at the frontier of deforestation events
where new human migrants are also arriving.
○
Africa
. Although data were too limited to take a longitudinal approach, the latest
data-rich assessment at multiple scales and using a pre-registered hypothesis
testing approach (which makes it less subject to selective interpretation) shows no
relationship between deforestation and malaria in Africa. Differences between
Africa and the Amazon are attributed to the fact that forest-human associations in
Africa are long-standing, and do not involve human migration to a deforestation
frontier (Bauhoff & Busch 2020). There are a few local ecological studies from
Kenya that suggest deforestation increases vectorial capacity of
Anopheles
gambiae
through changes in microclimates that influence sporogonic
development and mosquito reproductive fitness (Afrane et al. 2006, 2008).
● Schistosomiasis. In one studied region, dam construction degraded freshwater
ecosystems and led to local extirpation of native prawns. Restoration of these prawns,
which are ‘voracious predators of the snail intermediate hosts for schistosomiasis’,
reduced snail host abundance and as a result, human schistosomiasis prevalence
(Sokolow et al. 2017; Sokolow et al. 2015).
In one community, after adjusting for access to care, health district size,
and spatial trends, a 4.3% increase in deforestation was associated with a
48% increase of malaria incidence (Olson et al. 2010, Vittor et al. 2009, 2006).
9
Water-borne disease
There are examples of water-borne bacterial disease increases associated with ecosystem
degradation:
• Diarrheal disease in children. There is a significant association between tree cover in
upstream watersheds and probability of diarrheal disease among rural children under
age 5, as measured from a dataset from 35 developing countries. The effect of a 30%
increase in upstream tree cover is similar to the effect of improved sanitation (Herrera et
al. 2017).
• Typhoid occurrence. Fragmentation of riparian forests and density of roads crossing
creeks within a watershed is significantly related to incidence of typhoid in Fiji (Jenkins
et al. 2016).
Other established connections between environmental degradation and human health effects
include air quality, nutrition, pharmaceuticals and biomedical discoveries, mental health, access
to traditional medicines, endemic zoonotic diseases, and indirect effects on human health
through the impacts of climate change. More detailed coverage of these topics can be found in
the broad reviews by ILRI (2012), Romanelli et al. (2015), Rohr (2019), Kilpatrick (2017), and
Whitmee et al. (2015).
Guide in the Budongo Forest, Uganda, Julie Larsen Maher © WCS
SOLUTIONS AND RESPONSES
As described above, there are multiple clear lines of evidence pointing towards the conclusion
that declines in the integrity of ecosystems increase the global risk of zoonotic disease spillovers,
and hence the risk of pandemics. Enough is already known to identify the broad steps needed to
ensure that our interactions with nature occur in a way that lowers pandemic risk. It should be
acknowledged that the science is not complete and there are important questions to answer
before we know everything that we would ideally wish to know around the linkages between
the integrity of ecosystems and emerging zoonotic diseases. However, the precautionary
principle necessitates that strong action is taken while this additional research is undertaken
10
The One Health framework, adopted and championed by WHO, FAO, OIE, the Centers for
Disease Control, the World Bank, WCS and many other organizations and institutions, is a
widely applied approach to address zoonotic challenges (Waltner-Toews 2017; Gebreyes et al.
2014). The core One Health principle is that ‘communicable and non-communicable diseases
demand a truly comprehensive understanding of health and disease, and thereby a unity of
approach that is achievable only through convergence of human, domestic animal, wildlife,
plant, and environmental health, on a planetary scale’. One Health should be used as an
umbrella framework to find convergence among ecological and human health challenges. The
Berlin Principles
5
state, ‘going forward...we must overcome sectoral and disciplinary silos; apply
adaptive, forward reasoning, and implement multidisciplinary and multilateral solutions, while
boldly integrating current uncertainties to address the opportunities and challenges ahead’.
Ecological changes are important factors in driving disease outbreaks and as such need
increased levels of attention at international, national and local levels. One Health approaches
relating to the integrity of ecosystems must be placed in the context of how much land
degradation has already occurred in an area, and the ‘three conditions’ described by Locke et al.
(2019) are one useful way to frame these solutions. This framing recognises that there have been
diverse human influences on the Earth’s surface and it is possible, at least broadly, to categorize
landscapes by integrating nature-centric (what remains of nature) and human-centric (human
land-use) assessments of drivers and pressures on biodiversity. Three broad “conditions”
emerge:
• large, intact, mostly natural areas;
• ‘shared’, partially natural landscapes;
• farms and cities with very limited natural space remaining
According to each condition, broad suites of responses can be proposed to improve the state of
ecosystem integrity, to secure nature’s contributions to people, and minimise the risk of future
pandemics. These responses are outlined below. To be achieved, they need to be placed in the
appropriate policy, regulatory and legal frameworks, be supported by finance, engage the full
range of stakeholders in effective ways and be supported by additional science. It is beyond the
scope of this paper to discuss these critical aspects of implementation in detail.
In large wild landscapes we need to retain ecosystem integrity to the greatest extent possible as
by doing this we will minimize the various pathways that increase the risk of pandemics and
other spillover events.
• Maintaining ecosystem integrity means not modifying ecosystems beyond their natural
range of variation, which in practice means avoiding the expansion of large scale
extractive uses (e.g. industrial logging, large-scale harvest of animal and plant products),
not fragmenting areas with infrastructure, pastures and farmland, and not disrupting
natural fire and flood regimes.
• Since many of these areas are inhabited by, and protected by, Indigenous Peoples and
local communities, we must strengthen health care infrastructure to meet the needs of
these populations, and enhance emerging infectious disease surveillance in collaboration
with them (Munster et al. 2018) as well as better understanding the patterns of exposure
and immunity that they experience.
5
https://www.wcs.org/one-planet-one-health-one-future
11
In shared landscapes we need to manage significant ongoing levels of contact between humans,
wildlife and livestock, and be aware of factors (e.g. changing farm practices) that may increase
these levels. In this context we should consider nature-based or ‘One Health’ solutions that
support both human health and the restoration of ecosystem integrity to the fullest extent
possible.
6
Solutions that benefit both human health and environmental targets have the
advantage of contributing to multiple Sustainable Development Goals. A broad
recommendation for shared landscapes is that infectious disease interfaces and pathways that
have been created must either be removed or mitigated.
• Forest edges are an example of an interface that can be reduced in extent in some
settings, e.g. through restoration that reduces fragmentation.
• In other settings forest edge contact zones may be a part of the landscape that cannot be
reduced, in which case the focus should be on mitigating the risks they present.
7
• The commercial wildlife trade is an example of a high-risk interface that can and should
be removed in many cases, and whose risks should be mitigated in the remaining cases.
• Where restoration is not attainable, management decisions should nonetheless avoid
any further degradation of ecological systems
In the ‘third condition’ of the Locke et al. (2019) framework - highly human-dominated, farmed
and urban areas - there remain zoonotic diseases originating from wildlife, such as rabies from
bats or skunks, West Nile virus from birds via mosquito vectors, as well as tularemia, plague, and
hantavirus. Alongside these, such areas are also risky areas for emerging infectious disease
outbreaks from wildlife due to connections between remote source areas and urban and peri-
urban centres of demand for the wildlife trade.
• In these areas, commercial wildlife trade, particularly for human consumption, should
be halted and other forms of domestic animal trade should be improved to ensure
excellent hygiene standards. Public health, biosecurity and disease surveillance and
response systems tend to be more robust for known pathogens in these places, but
defences are less robust for the new, emerging pathogens that also occur in commercial
wildlife markets.
Julie Larsen Maher © WCS
6
see e.g. the Berlin Principles and IUCN’s new standards for Nature-based Solutions
7
For example, an intervention used after the discovery of Marburg, and Bombali and Zaire Ebolaviruses in West
Africa was as simple as information and resources on how to exclude insectivorous bats from homes and cover
food sources https://www.ecohealthalliance.org/living-safely-with-bats. In the case of Nipah virus in Bangladesh, a
simple tree skirt can prevent bats from urinating in vessels that are used to collect tree sap (Khan et al 2012).
12
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