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Animals can be sentinels of environmental
hazards for humans; for example, regularly monitoring the levels of dangerous
contaminants (eg lead) in pets can alert to the potential for poisoning of
children. Animals develop many of the same diseases we do and can thus be good
model systems. For example, dogs live for about 20 years making possible
long-term longitudinal studies to assess cancer risk as exemplified by the
Golden Retriever Lifetime Study. The discovery that ticks transmit cattle fever
germinated the idea of mosquito bites transmitting yellow fever and malaria.
Antimicrobial resistance in humans is directly traced to the use of antibiotics
in livestock and poultry.
Animals are an affordable and sustainable
source of protein for humans. But food security often comes at the risk of
deforestation, which can promote the spread of emerging viruses to humans. Ebola
and SARS viruses are directly transmitted to humans through eating infected
wild animals. Nipah virus was traced to pigs that were reared on deforested
land and got infected from fruit bats emerging from the lost forest.
Researchers are also exploring the role of pigs as intermediate hosts in the
transmission of Ebola virus.
In a landmark report in 20081,
Kate Jones and colleagues (Zoological Society of London, UK) analyzed emerging
infectious disease (EID) events between 1940 and 2004, with some startling
conclusions. The EID events had a non-random geographic distribution, were
dominated by zoonoses (i.e. transmission from animals to humans) of which over
70% originated in wildlife, and their origins correlated with socio-economic,
ecological and environmental factors.
Of almost 1500 pathogens known to infect
humans, over 60% are of animal origin. But these ‘known’ knowns appear to be a
small fraction of the total diversity. A 2013 study estimated 320,000 viruses
to infect mammals; if extrapolated to other species, there are an estimated 100
million viruses on our planet2. There is thus a vast pool of
‘unknown’ knowns.
What infectious agents are lurking in animals
that can jump into humans and cause disease? Are we at a greater risk of
zoonoses from apes, which share our genes, or rodents, which share our habitats?
With the devastating track record of zoonotic pathogens such as HIV, pandemic
influenza, Ebola and others, it would be sensible to address this
comprehensively.
Two recent studies3,4 report on
viruses spilling over from animals into humans and what drives such zoonotic
risk.
Olival and colleagues (EcoHealth Alliance,
USA) writing recently in the journal Nature3, analyzed associations
between 754 mammals and 586 viruses to understand what determines viral
richness, diversity and zoonotic potential. Bats, primates and rodents were
found to carry the highest numbers of zoonotic viruses. Bats are also a major
reservoir for coronaviruses, which made big news in 2002 when SARS emerged in
China, spreading to 27 countries and killing 774 people. In 2012, the newly
emerged MERS coronavirus caused 640 deaths.
Anthony and colleagues4 (Columbia
University, USA) studied coronavirus diversity in 12,333 bats, 3,387 rodents
and 3, 470 monkeys from 20 countries in Central Africa, Latin America and Asia,
which were previously identified by Jones as ‘hotspots’ for zoonoses. Nearly
10% of bats carried coronaviruses compared to only 0.2% of the other species,
with diversity being highest in locations that harbored multiple bat species,
such as the Amazon rainforest.
India
also has an an incredibly diverse bat population with 117 species and 100
sub-species5. But we know nothing about the viral diversity that it
harbors and its potential for causing human or animal disease.
The
Jones study should have alerted researchers and health policy people in India.
We and our immediate neighborhood are ‘hotspots’ for zoonotic, drug-resistant
and vector-borne pathogens. But there is little information from India, a key
country that is also missing from the Anthony study. Poor domestic research and
international collaborations in this area, the latter driven by restrictive
government policies on sharing clinical and research materials, are responsible
for it.
Professor
Ian Lipkin at Columbia University is a world expert in the search for novel
pathogens and a key contributor to the Anthony study. He has also tried to work
with India for many years. “Sample access is challenging”, says Prof. Lipkin.
He adds - “I'm eager to help (provided) the logistics can be sorted. Let's focus
on technology transfer in emerging infectious diseases. Global public health
and the people of India deserve our best efforts”.
Why is
India an EID ‘hotspot’?
The
transmission of infectious disease requires contact, and its probability
increases with population density. With a population of 1.34 billion people6,
512 million livestock and 729 million poultry7, and a land area of 3.287
million sq km8, India has a high density of about 400 people, 156
livestock and 222 poultry per sq km. High rates of human-animal, animal-animal
and human-human contacts increase the potential of emergence, circulation and
sustenance of new pathogens.
The International Livestock Research
Institute in Nairobi, Kenya, showed 13 zoonoses to cause 2.4 billion cases of
human disease and 2.2 million deaths per year. The highest zoonotic disease
burden, with widespread illness and death, is on Ethiopia, Nigeria, Tanzania
and India9.
India
has also lost about 14,000 sq km of forests over the past three decades, bringing
down its forest cover to 24% of land area10, against the recommended
one-third. This increasingly brings wildlife into contact with humans and domesticated
animals, adding to the direct risk of zoonoses from wildlife. Forest loss also
alters weather patterns, indirectly and unpredictably affecting zoonoses.
India presents a poor picture of One Health research, preparedness
and policy.
There are 460 medical colleges and 46
veterinary colleges in India, but most do little or no research. Limited
research on priority zoonoses such as influenza, tuberculosis, encephalitis and
others, happens primarily in the health sector, with the veterinary sector
paying little attention to human disease.
The governance structure and inter-sectorial
coordination is also problematic. The work on human health is guided by the
Ministry of Health and Family Welfare, that on animal health and husbandry by
the Ministry of Agriculture, and on the environment by the Ministry of
Environment and Forests. Each works in a silo.
India’s National Health Policy11
approved recently is also a missed opportunity. Framed to address the changing
national healthcare needs, it does not even mention the terms “zoonoses” and
“emerging infectious diseases”. It fails to break down the sectorial silos or
provide an enabling environment to build core capacity in key EID areas.
What must India do?
India has shown that various sectors can
successfully come together in a crisis situation such as during the 2006 Bird
Flu outbreak. The need is to move from being reactive to proactively understand
zoonotic pathogens before they emerge as disease in humans. This will require
preparedness and policy inputs.
An Inter-Ministerial Task Force involving the
key sectors of science and technology, human and animal health and the
environment could be entrusted with preparing a policy framework that enables
preparedness by strengthening research and health systems. Life scientists,
physicians, veterinarians and ecologists could be awarded collaborative
research grants to comprehensively survey animal species for pathogens with potential
for causing disease in humans.
The technology for pathogen discovery is not
complicated and is also available in the interest of global health. The
challenge is to come together.
Such research also makes economic and political sense.
Discovering the entire viral diversity on Earth is estimated to cost $6.4 billion2. In comparison, the World Bank estimates the 2002 SARS outbreak to have cost the global economy $54 billion, and a severe flu pandemic could cost about $3 trillion or 5% of the world economy12.
Discovering the entire viral diversity on Earth is estimated to cost $6.4 billion2. In comparison, the World Bank estimates the 2002 SARS outbreak to have cost the global economy $54 billion, and a severe flu pandemic could cost about $3 trillion or 5% of the world economy12.
A new disease emerging in any part of the
world is a global threat. If India aspires to be a future leader, it must take
this responsibility seriously. After all, if we can pledge to not
proliferate nuclear weapons, how can we remain a potential threat for disease
proliferation?
References:
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