The SARS-CoV-2 virus originated in mammals (most likely in bats, which will be the topic of the next review) and has spread to other mammals (especially people, of course). Birds are, well, birds, so they’re not mammals. Some viruses like both birds and mammals, but most don’t.
Researches have looked at this, and experimental infection studies have not resulted in evidence that birds are to any degree susceptible to SARS-CoV-2. This includes a study that looked at chickens, one that investigated chickens and ducks, and one that looked at chickens, turkeys, ducks, quail and geese. Those fit with the predicted poor susceptibility of chickens to SARS-CoV-2 based on their ACE2 receptor (the cellular structure the virus uses to attach to and invade cells – no attachment, no infection).
So, why bother investigating birds, since it wasn’t likely that they’d be susceptible to a mammalian coronavirus in the first place?
It was really important to check and verify that birds are low risk for a few reasons:
- There are massive numbers of domestic birds all over the world. That means lots of potential for exposure to infected people. If this virus got into a large group of birds (like on a poultry farm) and they were susceptible, there’d likely be big risks for the birds, as well as for transmission back to farm workers and issues with contaminated manure (just like we’re seeing in mink).
- Jumps to new species in large groups is a perfect recipe for unpredictable mutations (which has also been a concern in mink).
- Perhaps the biggest reason for wanting to know is simply that birds live everywhere we do, and beyond. There’s lots of potential for direct and indirect exposure of domestic (and wild) birds to this virus from human sources, and additional potential for contact between domestic birds and wild birds, which can then rapidly spread pathogens over long distances (as with avian influenza viruses). So, we needed to be confident that this virus couldn’t establish itself in any bird populations.
That’s why the work was done quickly at the start, and thankfully birds seem to be completely resistant to SARS-CoV-2.
(All that said, if you have COVID-19, don’t cough in your bird’s face. The non-scientific part of my brain still never wants to tempt fate.)