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Effect of climatic changes on the prevalence of
zoonotic diseases
1 2
Neelam Sachan and V.P.Singh
College of Veterinary Science and Animal Husbandry
Pt.Deen Dayal Upadhyay Pashu Chikitsa Vigyan Vishwa Vidyalaya Evam Go
Anusandhan Sansthan, Mathura-281001
1. Department of Veterinary Public Health Email- neelamvet@rediffmail.com
2. Department of Livestock Products Technology Email-vetvpsingh@rediffmail.com
Veterinary World, 2010, Vol.3(11):519-522 REVIEW
Abstract
Combustion of fossil fuels and human activities has led to sharp increase in greenhouse gases in the
atmosphere. These climate changes have tremendous effect on prevalence of zoonotic diseases. The
changes in climate may increase the insect vectors, prolong transmission cycles or increase the importation of
vectors or animal reservoirs. It may also have an adverse effect on biodiversity, distribution of animals and
microflora which may lead to emergence of zoonotic disease outbreaks. A historical perspective on major
vector-borne diseases such as arboviral encephalitides, dengue fever and Rift Valley fever, Lyme disease,
West Nile virus, malaria, plague, hantavirus pulmonary syndrome and dengue fever have been shown to have
a distinct seasonal pattern and in some instances their frequency has been shown to be weather sensitive.
Because of the sensitivities of the vectors and animal hosts of these diseases to climactic factors, climate
change-driven ecological changes such as variations in rainfall and temperature could significantly alter the
range, seasonality and human incidence of many zoonotic and vector-borne diseases. The evolution of
emerging zoonotic diseases globally during the period 1996 to 2007 was Ebola haemorrhagic fever, Rift Valley
fever, avian influenza H5N1, plague and Nipah virus. Whereas, bird flu and swine flu like diseases are still
creating havoc for human and animal health worldwide. It is a today’s and tomorrow’s demand that
interdisciplinary communication between health professionals, veterinarians, environmental scientists,
ecologists, geographers and economists seeking to understand climate change will be key to protecting
people in India and worldwide against these threats. Rigorous cross-disciplinary studies using a variety of
methodological tools will enable us to predict the transmission dynamics of diseases under different climate
scenarios and estimate the cost-effectiveness of mitigation strategies. In this text some of important diseases
which are dependant on global warming and climate changes have been discussed taken for and can change
their prevalence rate is considered for discussion.
Key words: Global warming, zoonotic diseases, avian influenza, swine flue, Japanese encephalitis, nipah
virus, rabies, leptospirosis
Global climate change is inevitable and the nitrous oxide is the largest climate driver and its rate of
combustion of fossil fuels has resulted in a build-up of increase during the industrial era is very likely to have
greenhouse gases within the atmosphere, causing been unprecedented in more than 10,000 years.
unprecedented changes to the earth’s climate. Human Furthermore, the carbon dioxide radiative forcing
activities have caused a sharp increase in greenhouse increased by 20% from 1995 to 2005. Significant
gases including carbon dioxide, nitrous oxide and anthropogenic contributions to radiative forcing were
methane in the atmosphere. These greenhouse gases also found to have come from several other sources
traps heat and light from the sun in the earth’s including tropospheric ozone changes due to
atmosphere which increases the temperature. Earth is emissions of ozone-forming chemicals, direct radiative
currently warming it is a reality and the factors forcing due to changes in halocarbons and changes in
responsible for this change are called climate drivers surface albedo due to land-cover changes and
and the relative impact or index of each factor’s deposition of black carbon aerosols on snow. However
importance to climate change is called its radiative the impacts of each of these factors were relatively
forcing. The scientists found that the combined small compared to the impacts of anthropogenic
radiative forcing due to increases in CO2, methane and greenhouse gases. Finally an increase in solar
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Effect of climatic changes on the prevalence of zoonotic diseases
irradiance since 1750 was estimated to have caused a examples of newly emerging zoonotic diseases. The
forcing that contributed to the recent warming of the direct and indirect socioeconomic impact of
earth. However, the impact of the increase in the BSE/nvCJD, SARS, avian influenza H5N1, and
amount of sunlight striking the earth each year during neglected zoonotic diseases such as rabies,
this ~250 year time span was estimated to be only brucellosis, cysticercosis and hydatidosis may gets
about 1/20th of the warming impacts of anthropogenic attention. The Bovine Spongiform Encephalopathy
greenhouse gas emissions. (BSE) like diseases needs to employ a complete ‘feed
Zoonotic diseases are defined those which can to food/farm to fork’ concept in food safety which in this
case required an international ban on the use of meat
be passed between vertebrate animals and humans.
and bone meal in animal feed for ruminants. The
The term was originally used to describe a group of
diseases that humans may acquire from domestic
human form of the disease nvCJD can also be
animals. This definition has since been modified to
transmitted through blood transfusion from humans to
include all human diseases that are acquired from or
humans and a study suggests that a significant number
transmitted to any other vertebrate. Infections may be
of potential blood donors in the United Kingdom (UK)
naturally transmitted between animals and humans.
may be incubating the disease. The true burden of
The majority of pathogen species causing disease in
zoonoses is difficult to estimate due to underreporting,
humans are zoonotic which are estimating over 60% of
misdiagnosis, insufficient laboratory diagnostic
all human diseases. Zoonotic diseases are common
facilities and lack of awareness among the public and
throughout the world and in developing countries it
health professionals.
constitutes an important threat to human health. A high
Avian influenza
proportion of notifiable human diseases are zoonotic.
They exclude diseases transmitted from human to
The avian influenza epizootic which commenced
in late 2003 severely affected poultry production and
human via an arthropod vector (e.g. malaria). Zoonotic
consumption and directly impacted the livelihood of
diseases have both direct and indirect effects on
millions of people. Given the cyclic pattern of pandemic
livestock health and production. Indirect effects occur
influenza outbreaks and ongoing exposure of humans
as a result of the risk of human disease, the viability of
to AI/H5N1 virus across the globe, there is every
livestock producers through barriers to trade, the costs
possibility that a potential pandemic influenza strain
associated with control programs, the increased cost of
may evolve. WHO, FAO and OIE work together through
marketing produce to ensure it is safe for human
a number of established detection and response
consumption and the loss of markets because of
frameworks including the Global Outbreak Alert and
decreased consumer confidence.
Response Network (GOARN), the Global Early
Important zoonotic diseases
Warning System (GLEW - WHO, FAO and OIE), the
Global warming, climate change and extreme
Information Network of Food Safety Authorities
(INFOSAN emergency -WHO/FAO) and the Crisis
weather events have an adverse effect on biodiversity,
Management Centre (FAO/OIE).
distribution of animals and microflora, all of which may
There are also frameworks aimed at
increase the likelihood of emergence of zoonotic
strengthening national surveillance and response
agents and infectious disease outbreaks. The
capacity under the International Health Regulations
emergence of the new cholera strain O:139 and
2005 (WHO), the Global Framework for progressive
outbreaks of West Nile virus, Rift Valley fever and
control of Transboundary Animal Diseases (GF-TADs -
Dengue fever in new geographical areas have been
FAO/O Zoonotic diseases are important in the SEA
linked with the El Nino oscillation. Bovine Spongiform
region because of the close everyday interactions
Encephalopathy (BSE) is transmitted from sheep to
between the human and animal world, deep-rooted
cattle and then from cattle to human beings in the form
sociocultural practices, high relative density of human
of the new variant Creutzfeldt-Jacob Disease nvCJD
and animal populations, intensification of the farming
as a consequence of human action. The spread of the
system, changing food habits and lifestyles of the
West Nile virus in the United States in recent years may
people. Avian influenza (H5N1) outbreaks were first
be linked to global warming and may have implications
reported in the SEA region in 2003. Sporadic outbreaks
for other vector-borne diseases. A historical
are continuing in many countries including in
perspective on major vector-borne diseases such as
Bangladesh (2007), India (2006-2007), Indonesia
arboviral encephalitides, dengue fever and Rift Valley
(2004-2007), Myanmar (2006-2007) and Thailand
fever may be considered.
(2003-2006). All these countries with the exception of
The evolution of emerging zoonoses globally
Indonesia adopted a stamping-out policy for the control
during the period 1996 to 2007 may be the concerned
and eradication of avian influenza outbreak in poultry.
issues. The Ebola haemorrhagic fever, Rift Valley fever,
Human H5N1 cases were reported from only Thailand
avian influenza H5N1, plague and Nipah virus are
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Effect of climatic changes on the prevalence of zoonotic diseases
and Indonesia. The major challenge in AI control is to should be urgently considered.
reduce human exposure to the H5N1 virus and if
Leptospirosis
possible to bring down the case fatality rate.
Leptospirosis is an emerging outbreak-prone
Swine flu
disease which is associated with flooding. Major
outbreaks have been reported from the states of
The viral infection is transmitted to humans who
Gujarat, Orissa, Maharashtra and Tamil Nadu in India
are in contact with swine; although there are several
cases of swine flu in people who had no known
and also in Northern Thailand during the last 10 years.
exposure to either infected people or pigs. Once the
Zoonoses control activities in India
species barrier is crossed, human to human
The importance of zoonoses in context of
transmission can occur with casual contact or airborne
emerging infectious diseases and socioeconomic
transmission like when one sneezes or coughs. Eating
development in India, it is utmost important to take care
pork products will not cause one to develop the swine
of these diseases. Avian influenza, Japanese
flu. Basically this flu is passed from one person to
encephalitis, Nipah virus, leptospirosis, plague and
another like any cold of flu infection.
anthrax are important zoonotic diseases commonly
The swine flu A (H1N1) is a viral infection that
found in India. The plague outbreak in Surat in 1994
originated from pigs and was first isolated from pigs in
provided a good opportunity to review the
the 1930s. The World Health Organization elevated the
preparedness levels to combat outbreaks of zoonotic
worldwide pandemic alert level to Phase 5, on April
diseases in India. A possible outbreak of SARS in 2003
29,2009. Phase 5 is called when there is a “strong
was averted through appropriate and timely measures
signal that a pandemic is imminent and that the time to
taken at ports of entry and by ensuring adequate
finalize the organization, communication, and imple-
preparedness for surveillance, laboratory diagnosis
mentation of the planned mitigation measures is short.”
and clinical case management. Avian influenza H5N1
Phase 6 is the highest level. On June 11th the 2010,
outbreaks in poultry during 2006- 2007 were contained
WHO raised the level to Phase 6 indicating that the flu
at source through coordinated action taken at the state
has spread worldwide.
and local levels and no human cases were reported.
Japanese encephalitis (JE)
Activities related to capacity building and streng-
thening laboratory and surveillance networks for early
JE is a major vector-borne zoonotic disease
detection and response for emerging zoonotic
endemic in most countries of the South Eastern Asian
diseases may take due attention. Pilot projects for
Region. The epidemiology of JE remains fairly stable in
rabies and leptospirosis have been incorporated in the
endemic countries except in those where vaccination
Eleventh Five Year Plan (2007-2011) of the Govern-
campaigns are introduced which have resulted in a
ment of India. The following strategies are of great
dramatic reduction in the incidence of disease in
importance in control of zoonotic disease in India and
normal conditions.
neighbouring countries:
Nipah virus
1. Advocacy, legislation, public awareness and
health education programmes should be
Nipah virus is another emerging regional
launched.
zoonotic disease of public health significance which
2. Appraisal of public health and socioeconomic
has been reported from Bangladesh and India. Little is
impacts of zoonoses should be taken care of.
known about the epidemiology and clinical
3. Strengthening of surveillance and disease
management of the Nipah virus and there is an urgent
investigation capacities in human and animal
need to strengthen capacity for surveillance and
populations is a urgent requirement.
laboratory confirmation.
4. Networking among epidemiological and
Rabies
laboratory units under public health and animal
health sectors are necessary step to be done.
Rabies remains a major public health problem in
5. Developing prevention and control strategies in
the Asian region. Dog-mediated rabies is responsible
animal hosts and vectors should be incorporated
for most human cases although cases of wildlife rabies
in the existing control programmes.
are also reported in the Indian subcontinent. Rabies
6. Development and harmonization of appropriate
vaccine of nerve-tissue origin is being phased out from
cross-border disease surveillance and response
India and Nepal. The introduction of a more cost-
activities is utmost important.
effective rabies vaccination schedule is required to
7. Medical and veterinary curricula with respect to
ensure that modern tissue-culture rabies vaccine
epidemiology and public health aspects of
becomes accessible to the general public. The
zoonoses should be modified.
implementation of a regional rabies control strategy
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Effect of climatic changes on the prevalence of zoonotic diseases
8. Involvement of medical and veterinary institutions, diseases involving multisectoral collaboration must be
launched.
NGOs, international professional associations
and animal welfare organizations in zoonoses
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