I’ll say it. I’m concerned about bird flu.

Uh, guys? Are you in the right headspace to receive information that could possibly hurt you? The Michigan Department of Health and Human Services announced yesterday that a second person in the U.S. this year has tested positive for H5N1, a highly pathogenic avian influenza virus. Like the first case reported in Texas last month, the Michigan resident had been exposed to cows infected with the virus while working on a farm. The Michigan DHHS press release doesn’t say much else about the farmworker, only that they “had mild symptoms and [have] recovered.”

We know a bit more about the Texas case, since researchers quickly published a case report in The New England Journal of Medicine. That person who contracted H5N1 worked on a dairy farm, and only experienced conjunctivitis from the virus. They told officials they came into close contact with both healthy and sick cows, and reported wearing gloves but not respiratory or eye protection. Some have speculated that they might have brought on the infection by getting infected milk in their eye.

So far, the new case in Michigan seems similar. According to the Centers for Disease Control and Prevention, a nasal swab from the person tested negative for H5N1, but an eye swab tested positive. Furthermore, the person’s only symptoms were eye-related. It’s not clear whether this Michigan resident used the same forms of protection when working with sick cattle. But pink eye is a less concerning symptom than signs of a respiratory infection: It’s easier to come into contact with tiny droplets from a cough or a sneeze than someone’s tears.

I’m getting ahead of myself, of course, because I went to public health school for infectious disease epidemiology and that sometimes draws me into thinking like a hammer looking for a nail. For H5N1 — or any zoonotic infection, for that matter — to develop sustained transmission in humans, the virus would need to acquire some key genetic differences. But in the classic model of zoonotic pathogen emergence, initial “spillover events,” where a disease jumps from an animal to a human, give way to cluster outbreaks where people get each other sick. I’m not calmed by the fact that these two spillover events occurred vast distances apart, suggesting that the characteristics allowing for spillover might be widespread. Nor do I feel great that we have growing evidence that farmworkers are shaping up to be particularly at risk. I’ve said this before in a Sequencer newsletter: disease surveillance can only work properly when people aren’t afraid of engaging with the healthcare system. Immigration status, fear of retaliation from an employer, or anxiety over having to quarantine and risk losing an income source — these are all factors that complicate public health efforts.

Even so, there are some concerning sides to H5N1 we haven’t seen yet, which is a relief, I guess. So far, H5N1 hasn’t been found circulating in pigs, which are more immunologically similar to humans than other livestock and harbor other flu strains that can already infect us. That’s an issue because influenza A viruses (the type H5N1 belongs to) can undergo a process called reassortment when two different viruses infect a single cell. The upshot of reassortment is that a virus lacking the genes to be good at infecting humans can very quickly acquire those tools to sustain transmission in humans. 

Disease surveillance can only work properly when people aren’t afraid of engaging with the healthcare system.

There’s also good news and bad news when it comes to the milk supply. When the Food and Drug Administration tested milk from retail stores across 17 states last month, one in five milk samples contained fragments of H5N1 (the bad news). The silver lining is that those are fragments; pasteurization eliminates the virus and so milk is still safe to drink. Of course, that means now is probably one of the worst times to get into drinking raw milk.

I do have some mixed feelings putting this post out into the world, potentially stoking concern while the CDC’s risk assessment for people remains low. But my fear is that we haven’t learned anything from COVID-19 and are doomed to ignore pandemic potential until it’s too late. I think that caution outweighs the risk of getting too worked up over a bird disease.