herd of deer standing under a holly tree in light snow

If you’re feeling COVID fatigue and seeking refuge in nature, last week’s announcement that deer tested positive for antibodies to SARS-CoV-2 is a real buzz kill. The news is spreading like a California wildfire in July. 

But do not despair. If you knew how many antibodies for which wild critters tested positive, you’d never eat sushi! That’s one reason it is not wise to handle wildlife. It’s for their protection as well as yours!

Let’s talk a little bit about what SARS-CoV-2 antibodies in deer really means and how disease surveillance in wildlife works. Disease surveillance is the ongoing, systematic, and continuous collection, analysis, and interpretation of health data. That’s a tall order fraught with difficulties when it comes to wildlife. Critters don’t readily line up for health checks annually. 

And surveillance can look for different things. Disease surveillance can target the clinical disease itself or it can target the pathogen which causes the disease. What is the difference? If you don’t have lots of animals looking or acting sick, you could miss a big problem – like avian influenza in ducks or CWD in deer. 

Disease surveillance takes 2 forms: passive and active. 

Passive surveillance needs a trigger. When someone reports a dead or sick deer, the animal is collected and may be tested for a variety of diseases like EHD, rabies, and CWD to name a few. Or current bird deaths in the mid-Atlantic. Looking for diseases like this is akin to answering the question “if a tree falls in the forest and no one is there, does it make a sound?” 

The number of things that needs to happen for that animal to make to the lab is anything but a sure thing. First, someone needs to know about it. Right now, there is a dead or dying deer, rabbit, squirrel, grouse, and warbler in the woods…and no one knows about it. Finding a dead or dying critter on the landscape is like trying to find a bite size Snickers™ bar in my house. Never going to happen! Second, it needs to be reported to the right people and collected tout de suite. Just because you have a body in hand doesn’t mean it’s worth anything – a dead critter is a scavenger and bug buffet! Viable samples wait for no man. And lastly, it needs to get to the lab. Hospitals are not located on every corner and wildlife diagnostic labs are even fewer and farther between. 

Active surveillance is that for which the army has been deployed looking for the enemy. The Game Commission collects deer heads each year to specifically look for the prion that causes chronic wasting disease (CWD) – testing lymph nodes and brainstems from thousands of deer that look completely healthy as well as those that clearly sick. The target has been selected and that is the only focus. This type of surveillance can be effective in finding a pathogen (the thing that causes the disease), but cost and feasibility of collecting representative samples can be a major problem as can the nature of the pathogen you are looking for. 

Passive and active disease surveillance are like dance partners. They complement and support each other helping disease ecologists and wildlife biologists understand pathogens and diseases. Active research then fills in the knowledge gaps. If there is one thing history has taught us, it is that emerging infectious diseases are increasing. 

White nose syndrome, West Nile virus, snake fungal disease, chytridiomycosis – are just a few emerging wildlife diseases whose discovery sent scientist on a quest to understand, define, mitigate, and manage them. 

But let’s get back to those COVID deer and the surveillance that found them. There are many diagnostic tests used in surveillance that either directly identify the pathogen (PCR, microscopy, immunoassays, etc.) or indirectly identify infections (serology, CBC/biochemistry, histopathology, etc.). All are great tools, but you need to know how to use them. 

In my hands, a router or a spokeshave are useless. Give them to Duane with a plan and he creates beautiful pieces of furniture.

Secretary desk with hand carved interior draws

But if you give me a pattern, a sewing machine, and a few hours, you’ll get a custom-made bag…or two. 

1 orange and 1 blue handmade purse with strap

It’s about using the right tools and interpreting the plans and patterns. The same can be said of diagnostic testing. 

USDA APHIS tested serum samples for white-tailed deer for antibodies to SARS-CoV-2. Antibodies were detected in 33% of the 481 samples. Samples were collected during 2020 in Illinois, Michigan, New York, and Pennsylvania. Samples tested pre-pandemic showed no sign of antibodies. 

All this means is that deer have been exposed to the COVID-19 virus and exhibited an immune response which resulted in the formation of antibodies. It did NOT detect the virus itself. Serology testing is fab but it can’t tell us if disease occurred (did deer get sick with COVID?), if the animal is protected from reinfection (could they get COVID again?), or when it was exposed (obviously post January 2020 but when and how?).

Here is where interpretation becomes important. This active surveillance alerted us to the fact that deer have been exposed and their immune system had a response. Nothing more. Serology testing is like a smoke detector. It alerted us to smoke. Now we can look to see if there is fire by researching the follow-up questions: Can deer show signs of disease if infected with SARS-CoV-2? Do deer shed live virus? Can deer be a reservoir for the virus? And the big question, can infected deer spread it to people or other wildlife? 

All of which cannot be answered from a simple antibody test. Misinterpretation or OVERinterpretation of diagnostic test results can create…confusion. Note this not limited to wildlife. The same can happen with diagnostic testing in people and pets! 

White-tailed deer are the most abundant and popular big game species in North America. It’s important to understand how pathogens may move through the population and affect deer and other species. 

But remember deer have always been walking biohazards (as are all wildlife). That’s why the advice has always been to avoid and limit exposure to wild animals. SARS-CoV-2 is just the new virus on the block. Rabies, anthrax, avian influenza, hantavirus – have been out there for years. 

There is still much to learn about SARS-CoV-2, wildlife, and people. We don’t need to panic but we need to stay informed, cautious, and vigilant until science can provide us more answers.  

I still eat sushi!

-Jeannine Fleegle
Wildlife Biologist
Deer and Elk Section, Game Commission

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