I’ve meant to write more about SARS-CoV-2 in deer, and USDA’s recent announcement of infected deer made me get my butt in gear (warning: long post approaching).
What do we know about SARS-CoV-2 infection in deer?
We now have three different pieces of evidence:
- Experimental infection
- It’s been known for a while that white-tailed deer are susceptible to SARS-CoV-2. Experimentally infected deer shed the virus and, importantly, were able to infect other deer. The ability to infect other deer raises obvious concerns about the ability to infect any other susceptible species (including humans). Since there are lots of deer in many areas, it also raised concerns that viral transmission could be maintained within some deer populations.
- Deer didn’t get sick in the experimental trials, apart from mild fever in some fawns. That’s good for the deer, but means we can’t use health status as a way of figuring out if the virus is circulating in a deer population.
- Serological data
- A month ago, the USDA reported antibodies against SARS-CoV-2 in 40% of tested deer in four US states (the full study description is now available in pre-print online). As I wrote in an earlier post about this observational study in deer, I thought it was very interesting and potentially concerning, but that we also needed more data before drawing any firm conclusions since it was such an unexpected finding.
- PCR and/or virus culture data
- The USDA recently announced identification of SARS-CoV-2 (the virus, not just antibodies) in deer in Ohio. Deer were sampled as part of other surveillance activities. This is perhaps the most interesting and concerning information so far.
- The report is light on details (e.g. testing method, number tested, number that were positive, sequencing info). Presumably, they were positive on PCR, and hopefully sequencing to determine the virus strain is underway. Consistent with the experimental study, infected deer were outwardly healthy.
- It’s not clear if this was a handful of deer from the same group, or multiple deer from several unrelated groups. Hopefully we’ll get more details on that soon too.
There are two broader concerns with these findings regarding SARS-CoV-2 in white-tailed deer:
- Reservoir for human infection: More infected individuals (human or animal) means more potential exposures for people. If this virus is present in deer (or other wildlife) that creates more opportunities for exposure.
- Potential for virus mutation: This is the big concern, but linked to the reservoir concern too. As I’ve said since this pandemic started, we really want to keep this a human virus – we don’t want it to spread to other species. Yes, it’s likely present in the original reservoir host population (presumably bats), but if it gets into other species, especially those that live closer to and interact more with people, and/or are present in larger numbers, the risk of a significant mutation occurring and spilling back into the human population increases.
Virus mutations are random events that happen all the time, but the more transmission there is, the opportunity the virus has to mutate. If there is sustained transmission in a wildlife population (or any population for that matter), it’s essentially guaranteed that new strains (variants) will develop over time. What that means in the bigger (human) picture could vary. Because they’re random, mutations can be good or bad for the virus, by making it either more or less transmissible, for example. What we’re concerned about is emergence of new variants that are more adept at infecting people and/or harder to prevent or treat, and those variants then finding their way from the animal population (in this case deer) back into people, and then spreading from person-to-person.
In the big picture, is SARS-CoV-2 in white-tailed deer a problem?
It’s hard to say. Currently, human-to-human transmission is still the problem. New mutations are going to develop in people because of widespread transmission internationally, and until we have good vaccine coverage everywhere (not just rich countries) we’ll have persistent and high risk of new variants emerging in people.
Deer probably contribute little to the risk, at least at this point. For a deer variant to be of concern, it has to find and infect a susceptible person, and human-deer contact is fairly limited in the grand scheme of things. It’s possible, but a susceptible person is still more likely to be infected by another person than by a deer at this point.
While SARS-CoV-2 remains a human pandemic, deer are likely a niche issue. As the virus eventually gets controlled in humans (we hope), then wildlife reservoirs become more important, if they can be a source of new variants.
What do we need to do?
We need more information, as usual. We need to know lots of things like:
- How widespread is infection in deer?
- What’s the likelihood that an infected deer would infect a person through routine contact (e.g. hunting, handling animals or carcasses)?
- Are variants emerging in deer?
- Are deer infecting other wildlife?
- Will transmission in deer be sustained, or (better for us) does this represent repeated short term transmission after introduction from people, or a rapid burn through the population?
This is one of those “let’s pay attention and get more info, but not freak out” situations. Throughout this pandemic, I’ve tried to balance increasing awareness with avoiding excessive concern or paranoia, and that applies here.
What should deer hunters do?
- Get vaccinated.
- Hunt with vaccinated people.
- Use standard COVID-19 precautions around people.
Should hunters do anything specific when handling deer?
I don’t think we have enough evidence at this point to make specific recommendations for hunters handling deer. Good general hygiene is obviously important, but whether hunters should take extra precautions (e.g. mask and eye protection) is completely unclear. As we learn more, it’s possible that guidance will change.
What about venison?
There should be essentially no food safety risk when it comes to consuming venison. This virus does not survive well outside the host, so even if the animal was infected, the risk from handling meat is presumably negligible. Good hygiene practices used when handling raw meat of any kind should cover any theoretical risk. It’s always important to cook meat properly before consuming it as well, and the virus would not survive that process either.
My usual ending for these posts is a reminder that COVID-19 is ultimately a human issue. Animal infections are a result of human activities and human contacts. The best way to reduce the risk of this virus entering animal populations is to control it in people.
Human vaccination is probably the best protection for deer.