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Earth

COVID-19 Wildlife Connection

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With new cases of coronavirus (COVID-19) still being reported every day across the globe, we are starkly reminded that handling or coming into close contact with wildlife, their body parts, and excreta poses a risk of spillover of the pathogens [viruses, bacteria, parasites, and fungi] they host and maintain in nature, and to which we humans might be susceptible.

The illnesses animals spread to humans are known as zoonotic diseases, or zoonoses.

It is estimated that, globally, about one billion cases of human illness and millions of deaths occur every year from zoonoses. Some 60 percent of emerging infectious diseases that are reported globally are zoonoses and of the more than 30 new human pathogens detected in the last three decades, 75 percent have originated in animals.

A wide variety of vertebrates are carriers of zoonotic agents. Rodents, the most abundant mammal, also represent an abundant source of zoonotic diseases, carrying at least 180 unique zoonotic pathogens[1]. Because of their size, the ability to fly and their unique immune system, bats represent an important virus reservoir, though presently they are known to carry only about a third of the zoonotic pathogens that rodents do.

While there are fewer species of primates when compared to rodents and bats, a great proportion are zoonotic hosts. The risk that pathogens can infect humans increases with species more closely related to us. For example, the spillover of HIV to humans occurred from chimpanzees and sooty mangabeys, most likely through butchering and consumption of their meat. To date, HIV-AIDS has infected 75 million people and caused 32 million deaths[2].

Graphic design: Sarah Markes/WCS.

The persistent lethal capacity of zoonotic pathogens can also reside in its evolutionary strategies. Plague is a bacterial, vector-born disease transmitted by fleas from rodents –its natural reservoir– to humans and subsequently also from humans to humans that has impacted the history of mankind through multiple pandemics causing tens of millions of deaths worldwide. The responsible bacterial agent has evolved virulence factors that have allowed it to repeatedly and successfully evade the immune system of the mammalian host[3].

“Coming into close contact with wildlife — including their body parts and excreta — poses a risk of spillover of the pathogens they host, to which we humans might be susceptible.”

Zoonoses may exist in various forms: The most common, endemic zoonoses, are widespread in developing countries affect many people and animals and are by comparison mostly neglected by the international community, epidemic zoonoses vary widely in their duration and distribution and emerging and re-emerging zoonoses may or may not have occurred previously in a given population, but are generally observed to expand in new species, populations or areas.

Emerging infectious diseases (EIDs) and particularly zoonotic ones are a significant and growing threat to global health, global economy and global security. Analyses of their trends suggest that their frequency and economic impact are on the rise.

The conditions of so-called “wet markets” are ideal for incubating new diseases and bolster their transmission. Photo credit: Elizabeth L. Bennett/WCS

Recent examples of such emerging or re-emerging zoonoses include Rift Valley fever, severe acute respiratory syndrome (SARS), pandemic influenza, Yellow fever, Avian Influenza, West Nile virus, the Middle East respiratory syndrome coronavirus (MERS), and most recently COVID-19.

However, our current knowledge of zoonotic diseases and spillover mechanisms is still at its infancy. It is estimated that less than 0.1% of all viruses that may pose a threat to global health are now known to have been transmitted from animals to humans[4].

More than 300,000 viruses are estimated to await discovery in mammals, many of them bearing zoonotic potential. In the U.S.-funded PREDICT program, researchers estimate that there are more than 1.6 million unknown viral species in mammals and birds, 700,000 of which could pose a disease risk to humans, based on years of information gathering.

“In wet markets across the globe, live and dead animals — including many wildlife species — are sold for human consumption.”

Facing such a vast, unknown and unpredictable universe of zoonotic agents, we firmly believe that limiting the chances of contact between human and wild animals is the most effective way to reduce the risk of emergence of new zoonotic diseases.

In “wet markets” across the globe, live and dead animals — including many wildlife species — are sold for human consumption. In close quarters, a mix of saliva, blood, urine and other bodily fluids brush up against vendors and consumers alike. The conditions of these markets are ideal for incubating new diseases and bolster their transmission. They form one of the most detrimental bridges created by man over the natural barriers that previously separated humans and wild animals.

Destruction of nature is increasingly putting humans in contact with pathogens for which they have no natural immunity. Photo credit: Nick Hawkins

For example, in 2016, two officials from the Department of Livestock and Fisheries in Lao PDR, Drs. Bounlom Douangngeun and Watthana Theppangna along with One Health experts authored a paper which documented that wild mammals from 12 taxonomic families and capable of hosting 36 different known zoonotic pathogens were traded in only seven markets[5]. It is a similar situation that has enabled the emergence of the previously unknown SARS in central Guangdong Province in November 2002 and now COVID-19 coronavirus in Wuhan, China.

“Ignoring the danger posed by wildlife markets is a massive global public health liability for a healthy world.”

The interface within these wet markets has been largely ignored as a public health topic, but COVID-19 coronavirus has brought this interface back to the forefront and reminded us that ignoring the danger posed by wildlife markets is a massive global public health liability for a healthy world.

As Dr. Christian Walzer emphasized recently this is a “global health priority that cannot be ignored.” It is important to continue calling for three solutions to prevent this complex global challenge: close live animal markets that sell wildlife; strengthen efforts to combat trafficking of wild animals within countries and across borders; and work to change dangerous wildlife consumption behaviors, especially in cities.

For the Silo, Stephen Sautner- Executive Director of Communications, Wildlife Conservation Society- Bronx Zoo

NOTES

[1] Cleaveland et al. 2001. Diseases of humans and their domestic mammals: pathogen characteristics, host rage and the risk of emergence. Phil Trans R Soc Lond B 356, 991–999

[2] Huet T, Cheynier R, Meyerhans A. et al. « Genetic organization of a chimpanzee lentivirus related to HIV-1 » Nature 1990, 345;356–9.

Santiago ML, Range F, Keele BF, Li Y, Bailes E, Bibollet-Ruche F, Fruteau C, Noë R, Peeters M, Brookfield JF, Shaw GM, Sharp PM, Hahn BH (2005). “Simian Immunodeficiency Virus Infection in Free-Ranging Sooty Mangabeys (Cercocebus atys atys) from the Tai Forest, Cote d’Ivoire: Implications for the Origin of Epidemic Human Immunodeficiency Virus Type 2”. Journal of Virology. 79 (19): 12515–27.

https://www.unaids.org/en/resources/fact-sheet

[3] Demeure C.E., Dussurget O., Mas Fiol G., Le Guern A.-S., Savin C., & Pizarro-Cerda, J. 2019. Yersinia pestis and plague : an updated view on evolution, virulenvce determinants, immune subversion, vaccination and diagnostics. Genes & Immunity 20, 357–370.

[4] http://livescience.ecohealthalliance.org/predict/reports/2018-04-16-edi-measuring-viral-discovery.pdf

[5] Zoe F Greatorex & Sarah H Olson & Sinpakone Singhalath & Soubanh Silithammavong & Kongsy Khammavong & Amanda E Fine & Wendy Weisman & Bounlom Douangngeun & Watthana Theppangna & Lucy Keatts & Martin G, 2016. “Wildlife Trade and Human Health in Lao PDR: An Assessment of the Zoonotic Disease Risk in Markets,” PLOS ONE, Public Library of Science, vol. 11(3), pages 1–17, March.

Culture

Wildlife Supply Chains for Human Consumption High In Coronaviruses

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HA NOI (June, 2020) – A new study found that animals sampled in the wildlife-trade supply chain bound for human consumption had high proportions of coronaviruses, and that the proportion of positives significantly increases as animals travel from traders, to large markets, to restaurants.

The study, which appears in the pre-print journal bioRxiv, is by a team of scientists from WCS, the Department of Animal Health of the Viet Nam Ministry of Agriculture and Rural Development, Viet Nam National University of Agriculture, EcoHealth Alliance, and One Health Institute of the University of California, Davis.

Wildlife in the trade supply chain are often under stress and confined at high densities with other animals from multiple sources which likely results in increased shedding of coronaviruses. The authors forewarn of the potential risk of viral spillover into people through the wildlife trade.

The authors indicate that stress and poor nutrition likely contribute to decreasing animal immune functions resulting in increased shedding and amplification of coronaviruses along the supply chain. The findings in rodents illuminate the potential for coronavirus shedding in other wildlife supply chains (e.g. civets, pangolins) where similarly large numbers of animals are collected, transported, and confined.

The purpose of the study was to gain a better understanding of coronavirus presence and diversity in wildlife at three wildlife-human interfaces including live wildlife trade chains, wildlife farming, and bat-human interfaces. This work represents an important demonstration of capacity and a significant contribution from Viet Nam to the field, laboratory, and scientific approaches critical to understanding and addressing zoonotic disease threats. The consensus PCR approach for viral detection is a cost-effective tool for detecting both known and novel viruses and co-infections in a variety of taxa, sample types, and interfaces.

Researchers collected samples at 70 sites in Viet Nam, and detected six distinct taxonomic units of known coronaviruses. There is no current evidence to suggest these particular viruses were a human-health threat, but the laboratory techniques used in the study can be utilized to detect important emerging or unknown viruses in humans, wildlife, and livestock in the future.

The team found high proportions of positive samples among field rats destined for human consumption. The proportion of positives significantly increased along the supply chain from traders (21 percent), to large markets (32 percent) to restaurants (56 percent). Coronaviruses were detected on two-thirds of the surveyed wildlife farms, and six percent of rodents raised on the farms were positive. A bat and a bird coronavirus were found in rodent fecal samples collected from wildlife farms suggesting either environmental mixing or viral sharing among species. Coronavirus detection rates in rodent populations sampled in their ‘natural’ habitat are closer to 0-2 percent.

Said Amanda Fine, WCS Health Program Associate Director, Asia, and a co-author of the study: “Wildlife supply chains, and the conditions the animals experience while in the supply chain, appear to greatly amplify the prevalence of coronaviruses. In addition, we documented exposure of rodents on wildlife farms to both bat and bird coronaviruses. These high prevalence rates and diversity of coronaviruses, added to the species mixing we see in the wildlife trade, creates more opportunities for coronavirus recombination events as well as spillover.”

The authors warn that the trade in wildlife facilitates close contact between people and multiple species of wildlife taxa shedding coronaviruses. This provides opportunities for intra- and inter-species transmission and potential recombination of coronaviruses.

The wildlife supply chain from the field to the restaurant provides multiple opportunities for such spillover events to occur. To minimize the public health risks of viral disease emergence from wildlife and to safeguard livestock-based production systems, the authors recommend precautionary measures that restrict the killing, commercial breeding, transport, buying, selling, storage, processing, and consuming of wild animals.

The emergence of SARS-CoV, MERS-CoV, and now SARS-CoV-2 highlight the importance of the coronavirus viral family to affect global public health. The world must increase vigilance through building and improving detection capacity; actively conducting surveillance to detect and characterize coronaviruses in humans, wildlife, and livestock; and to inform human behaviors in order to reduce zoonotic viral transmission to humans. 


Hoang Bich Thuy, WCS Viet Nam Country Program Director and co-author explains: “Since the outbreak of COVID-19, the Government of Viet Nam has been taking strong actions to enforce wildlife trade laws and is considering the prohibition of wildlife trade and consumption as directed by the Prime Minister in his Official Letter No. 1744/VPCP-KGVX dated 6 March 2020 of the Government Office. This research provides important baseline information and suggests areas for targeted studies to provide more evidence for the development of new policies and/or revision of the legal framework in Viet Nam to prevent future pandemics by mitigating risks of transmitting pathogens from animals to humans at key nodes along the wildlife supply chain. Successful interventions will be those that support a significant reduction in the volume and diversity of species traded, and the number of people involved in the trade of wildlife.”

This study was made possible USAID’s Emerging Pandemic Threats PREDICT project with cooperation from the government of Viet Nam.

WCS (Wildlife Conservation Society)

MISSION: WCS saves wildlife and wild places worldwide through science, conservation action, education, and inspiring people to value nature. To achieve our mission, WCS, based at the Bronx Zoo, harnesses the power of its Global Conservation Program in nearly 60 nations and in all the world’s oceans and its five wildlife parks in New York City, visited by 4 million people annually. WCS combines its expertise in the field, zoos, and aquarium to achieve its conservation mission. For the Silo, Stephen Sautner, Wildlife Conservation Society, Bronx Zoo, New York.

Featured image- Civet in a farm in Dong Thap, Viet Nam.  CREDIT: ©WCS Vietnam