Wildlife Diseases and Pandemics

April 29, 2020 | Causes and Possible Solutions



NCEL Point of Contact

Kate Burgess
Conservation Program Manager


Zoonotic diseases, or zoonoses, are caused by the transfer of germs between humans and non-human animals. Taking the form of bacteria, viruses, parasites, or fungi, these germs can be spread to humans through direct physical contact, through intermediate hosts like wildlife or insects, or through the air. Most often, wildlife are carriers of these diseases, meaning that they are able to transmit the illness without experiencing symptoms. Humans, however, carry no natural immunity to many of these diseases, and thus are often placed at high risk of serious illness or death. Zoonotic diseases, including the COVID-19 pandemic, are on the rise because of climate change, loss of habitat including deforestation, and wildlife trafficking.

Six out of 10 infectious diseases are zoonotic and three out of four new or emerging infectious diseases are zoonotic.

Historic Examples and Spread of Wildlife Diseases 

We are familiar with many of these diseases already: SARS, rabies, yellow fever, swine and other zoonotic flu, Lyme disease, and West Nile virus are all examples of zoonoses. Recently COVID-19 and Ebola have joined this list, and are particularly notorious for their extensive outbreaks, deadliness, and ability to spread quickly around the world.

Human-wildlife interactions have drastically evolved over time, and as climate change, human populations and deforestation have expanded, so have methods of zoonosis contraction. 

For centuries, domestic animals transmitted most zoonotic diseases to humans (such as ringworm from house cats). Then as humans encroached on wild animal habitats through development, deforestation, and other land conversions, the risk of transmission to humans from non-domesticated species increased due to the higher rates of contact. This is also in part due to climate change. For example, rising temperatures have allowed mosquitoes to expand their range to new populated areas, and caused wildlife to move to cooler areas. In addition, the wildlife trade and wildlife trafficking have also put humans into close contact with new species, including rare, threatened and endangered species, many of which are disease hosts.

Examples of Common Zoonoses by Species

  • Bats: Ebola, SARS, rabies; potentially COVID-19
  • Mosquito: Malaria, Dengue fever, Zika, West Nile, yellow fever
  • Ticks: Lyme disease, Rocky Mountain spotted fever
  • Rodents: plague, salmonella, hantavirus
  • Birds: bird flu (H1N1, H5N1), salmonella
  • Cats: ringworm, toxoplasmosis
  • Pigs: swine flu
  • Cows: E.coli, salmonella, brucellosis

COVID-19 and Its Connection to Wildlife

Humans have exacerbated the spread of zoonotic illnesses through the sale of wild animals in seafood and live animal markets, such as in Wuhan, China, where the new COVID-19 strain of coronavirus is thought to have originated. These wet markets have allowed for direct contact with disease-carrying wildlife – in addition to their excretions like spit, blood, and urine that contribute to the “wet” prefix. According to the Center for Disease Control, coronaviruses are common in both people and many different species of animals, including bats, cats, cattle, and camels. The stress on the animals and the close proximity of these market environments enables the virus to more easily spread to animals and humans.

Zoonoses typically end with humans, meaning we don’t see transmission back to animals. However, in April 2020 a Malaysian tiger tested positive for COVID-19 at the Bronx Zoo and other tigers and lions in that zoo have also tested positive. A similar transmission has occurred in Hong Kong and New York City, where multiple cats and dogs have tested positive following their owner’s diagnosis. This new development raises questions regarding human ability to transfer the virus to animals, especially the susceptibility of other domestic animals such as livestock, upon whom people rely for food. 

Policy Options

Zoonoses can be difficult to control because their range transcends political boundaries, but there are policy options that can be pursued.

International Policy Options

At the international level, one preventative option is to create and enforce stronger wildlife trafficking bans. China, for example, has banned the trade and consumption of wild animals in the wake of COVID-19, similar to its temporary ban in 2002 due to the SARS outbreak. This ban encompasses not only wild animals traded for human consumption, but also endangered species recognized under CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora). 

In East Asia, while bans like this would appear to be effective policy moves, they can be difficult to enforce because of the strong cultural and social traditions that support consumption. Many animal products, for example, are favored for traditional medicines, which hinders efforts to enforce this policy. Others, like the pangolin (another potential COVID-19 intermediate host in question and the most heavily trafficked mammal in the world) are considered to be delicacies. Effective permanent bans will require strict enforcement; attention to and empathy for the changing of livelihoods and culture of those who are no longer able to consume wild animals; and surveillance of and monitoring for the development of underground markets. 

While the situation in East Asia is somewhat complicated, nations can and should do their part to uphold international CITES restrictions on wildlife trade on their own soil. Nations should also participate in the World Health Organization’s GLEWS animal disease rapid reporting and information sharing system. GLEWS stands for Global Early Warning System for Major Animal Disease, including Zoonoses. 

Federal Policy Options

Between 2005 and 2014, nearly 50,000 illegal wildlife shipments entered U.S. ports. Despite existing legislation like the Lacey Act, which prohibits the trade of wildlife that are recognized under CITES, the wildlife trade is still incredibly active. Enforcement in this regime can be improved with more robust funding and programmatic support. The U.S. has been hit particularly hard by COVID-19 and has the opportunity to take a leading role in combating not only further illegal wildlife trafficking, but also implement strategies to prevent the spread of deadly illnesses.

Policy options include:

  • Fund inspection and enforcement of illegal wildlife trafficking
  • Fund the investigation of drivers of demand for wildlife trafficking in the U.S.
  • Develop improved monitoring of timber sales (around 25% of globally traded timber is from illegal logging operations. Deforestation exposes logging workers and communities on the frontline to new pathogens as wildlife is displaced)
State Policy Options

States, especially those with ports, have the opportunity to better regulate in-state sales of wildlife parts and products, as well as expand existing restrictions to include more species that are recognized under CITES that may be disease vectors. Many states are starting to include more CITES-listed species in their wildlife trafficking bans. As we have seen with COVID-19, a lack of control over wildlife trade and trafficking can have colossal impacts on both global and national health.


Zoonoses and resulting pandemics from human infection have the potential to become even more common and deadly without further intervention. Wildlife trafficking and trade has contributed, and perhaps even driven, the pervasiveness of these diseases. However, it’s possible to reduce the likelihood of epidemics like COVID-19 with stronger global, national, and state regulation and enforcement of wildlife trafficking. Nations and states can also take more action to prevent zoonotic pandemics by reducing the exploitation of nature that increases wildlife-human interactions.