Conservation Column: Diseases Respect No Boundaries

I hope that everybody is safe and well as we deal with this devastating pandemic. Turns out that many of the conservation issues that have been on our radar for years are associated with pandemics. Zoonotic (zōe’nätik) diseases are caused by pathogens that jump from other species to us. They can be particularly problematic because we have no previous immunity. Hence the term “novel” with this coronavirus. The Wildlife Conservation Society estimates that about one billion cases of human illness and millions of deaths occur every year from zoonotic diseases, and that 60 percent of known infectious diseases in people were transmitted from animals. 

Zoonotic diseases are more likely to spread and to jump species when animals are crowded together and when they come into close contact with other species. The tremendous numbers of people (more than seven and a half billion) living on the earth need food and places to live resulting in extensive habitat conversion. As animals lose habitat, their remnants live in higher densities and become less able to stay clear of people. Logging, mining, road building through remote places, expanded agriculture, and rapid urbanization all bring humans into closer contact with animals that typically live apart. Human encroachment into previously undisturbed habitat not only leads to biodiversity loss, it increases the risk of transmitted diseases. Combine this with wildlife trade (both legal and illegal) and you have the current recipe for disaster.

Some evidence suggests that this new coronavirus originated in bats. But are bats to blame? When a bat is stressed due to being hunted and having its habitat damaged by deforestation, her immune system is challenged making it harder to cope with pathogens that would otherwise be quickly suppressed. Now crowd that bat in with another animals (there may have been an intermediate host) and with humans, and the situation creates an increased likelihood of a pathogen jumping species. The jump for COVID-19 putatively occurred in what is termed a “wet” market meaning that live animals that typically have little contact are crowded together under unsanitary and stressful conditions. Conditions in these markets are ideal for incubating new diseases and boosting their transmission. Due to the devastation of the virus, China has made eating wild animals illegal. However, there are wet markets all over the world and, even in China, enforcement will be difficult. We need to focus on wildlife trade in a determined manner and on a much broader scale, to reduce disease risk and save animals from overexploitation.

But it is not just wet markets that foster epidemics. Concentrated animal feeding operations and factory farms that produce meat have been the source of several disease outbreaks, including the many strains of swine flu and avian flu. For example, H1N1 swine flu was an outbreak from a pig confinement operation in North Carolina. China and India’s bird flu outbreaks began among their chicken factories. Not to mention the antibiotic resistant bacterial diseases such as methicillin-resistant Styphylococcus aureus (MRSA) and salmonella that propagate there. 

In addition to habitat destruction, wildlife trade, and the meat industry, we are grappling with another environmental issue that has devastating potential to increase diseases worldwide. A number of diseases that are climate-sensitive, such as malaria, dengue fever, West Nile virus, cholera, and Lyme disease, are expected to worsen with climate change. One mechanism is by expanding the range of many vector-borne diseases, particularly mosquitoes that carry diseases, such as malaria or Zika. Further, an increase in sudden and extreme weather events may change food availability causing animals to gather together and transmit disease, as is suspected in the recent Ebola outbreak. These phenomena may also directly affect people’s ability to fight infection. For instance, droughts and floods affect crop yield, while malnutrition and stress make people more vulnerable to disease. 

Deforestation and burning fossil fuels are linked to increased emissions and air pollution. Pollution exacerbates a number of health issues, including respiratory diseases such as asthma. People with these diseases are particularly susceptible to corona viruses, including the COVID-19 outbreak. Ironically, the shelter-in-place policies are reducing pollution in a number of places worldwide, including India, China, and Los Angeles. However, the current administration has relaxed all enforcement by the EPA of pollution regulations and has rolled back America’s Clean Car Standards. This is the very opposite of their stated mission to protect human health and the environment. We must implore government to address the environmental issues that threaten our health. I like the idea of “One Health,” an approach being embraced by the CDC to advance the knowledge that the health of people is closely connected to the health of animals and our shared environment. We are all in this together.