Covid and the Human-Wildlife Interface

     A variety of zoo animals are becoming infected by Covid19. Some are dying from the disease. Although we can’t be certain, it seems likely these captive wild animals are contracting the disease from zoo workers and human visitors. The susceptibility of some zoo animals to Covid only reinforces health officials’ concerns that wildlife may become a reservoir for Covid’s persistence and continuing threat to mammalian species, including us. Testing of whitetail deer in several Midwestern states has revealed that about one third of sampled animals have tested positive for exposure to SARS-CoV-2, the virus that causes human Covid. Research on the virus’s pathogenicity in whitetails is ongoing. Even if it doesn’t cause significant disease in deer, this abundant wildlife species (an estimated 30 million whitetails inhabit North America) could harbor the virus for some time.

     We think of zoonotic diseases as those that can be passed from animals (wild or domestic) to humans. Almost 70% of all infectious human diseases are of animal origin. A few examples are SARS, HIV Aids, Lyme disease, rabies, and all influenzas. However, wild animals also run the risk of infection, disease, and mortality from transmissible zoonotic diseases contracted from humans. Spillover can go both directions.

I visited Uganda to see mountain gorillas a number of years ago. Before trekking into the Bwindi Impenetrable Forest to spy on a habituated gorilla group, park officials went to great pains to orient us about the risks and precautions to prevent transmission of human respiratory pathogens to gorillas. As one of our closest relatives, gorillas are susceptible to many human diseases. And that includes Covid. But gorillas are certainly not alone.

     Whitetail deer (and likely other wild, free-ranging species) are contracting Covid19 from humans. Given our close association with millions of deer, and the virus’s transmissibility, this is unsurprising to epidemiologists. In deer the virus could further mutate into variants that may potentially reinfect humans. For example, a variant of Covid that developed in Dutch mink farms in 2020 spilled back into mink farmers. This, of course, complicates fighting Covid in humans.

     These realities are unsettling and undeniable reminders of our kinship and connection to other species with which we share the planet. And reminders that we’re one of many components of the elaborate biophysical edifices we call ecosystems. Not only more complex than we think, ecosystems are more complex than we can think.