Hi! Welcome to episode 21 of the Public Health Report, where we discuss current events in the public health sphere. I’m your host this week, Lizzie Wilson, and today we’re diving into the emerging public health threat that’s making a lot of headlines lately, and that is avian influenza H5N1.

On Wednesday, February 8th, the director of the World Health Organization made an announcement concerning H5N1 in minks, otters, and sea lions. Now, typically these avian influenza A viruses affect aquatic birds, but sometimes they also affect poultry and other animals as we see here.

You may have heard about the outbreak of H5N1 at a mink farm in Spain. It occurred in October and was reported on in Eurosurveillance on January 19th[i].

Here’s what happened: At the beginning of October 2022, mink farm workers noticed that the animal’s mortality rate jumped from 0.25% up to 0.77%. At this point, they began testing the animals for viruses, including H5N1 and SARS-CoV-2, and found that they tested positive for H5N1. The disease appeared to spread in hotspots around several pens, leading many minks to become infected with H5N1, and ultimately all 51,986 animals were culled. However, despite coming into contact with infected minks, no farm workers tested positive for the virus.

A news article published in Nature last week explains why this particular outbreak is concerning[ii]. Unlike in past outbreaks of H5N1, this one demonstrates mammal-to-mammal infection. Previously, all infections in mammals could be attributed to contact with materials contaminated with the virus, such as bird droppings or infected feed. But in this case, poultry farms supplying feed to the mink farm did not experience outbreaks of H5N1, and it is likely that infected wild birds—attracted by the mink’s food— entered these high-density open air cages were minks are kept, and the virus eventually jumped species and then spread amongst minks[iii].

Currently, H5N1 is not efficiently and sustainably transmitted between humans. And that bears repeating: The current threat to human health is low. In fact, the New York Times reports that globally only 10 cases of H5N1 have been reported in humans since December of 2021—notably with 0 reported cases of human-to-human transmissioniii. However, in cases of human infection of H5N1, WHO reports a 56% case fatality rate[iv].

There are some warning signs that could make human-to-human transmission (and a pandemic) more likely. Let’s briefly touch on those:

·      So first, H5N1 is infecting a larger number of migratory birds, which raises the risk of a new variant spreading to people.

·      Second, H5N1 infected minks, and likely spread mammal-to-mammal in October. This is unprecedented, and it’s especially alarming because the upper respiratory tract of minks is a very good conduit for humans[v].

·      Third, if a farmer infected with a different strain of influenza were simultaneously infected with H5N1, these viruses could undergo reassortment–a process of swapping genes during co-infection—and potentially create a virus that is more transmissible between people[vi]. Indeed, a 2021 study in Emerging Microbes and Infections found that minks are commonly infected with both human and avian influenza A viruses, making them an ideal species for reassorting these viruses—and these researchers recommend taking steps to minimize contact with raw poultry products as well as taking urgent steps to increase