Dropping from the Sky

What’s up with Avian Influenza?

words :: Leslie Anthony

Early in the summer, those who pay attention to such things may have noticed yet more twists to the now three-year global saga of Avian Influenza A(H5N1). If you subscribe to the daily ProMED Digest of global disease outbreaks in plants, animals and humans (recommended reading—though it might affect your sleep), you’ll have been treated to regular updates as the virus burned through birds, into marine mammals, into land mammals (both wild and pets) and on into American dairy cattle. That’s bad enough, but further reports suggest a widespread global disease situation that seems entirely out of hand and primed to cause more problems with entries like this: Avian influenza—USA (WY, IA) H5N1, dairy cows, unreported fatalities; Avian influenza—USA (NM) house mouse; Avian influenza— Cambodia, human H5N1, 10 cases, fatal, and; Avian influenza— Mexico, human H5N2, fatal.

We’ll unpack how those are related in a minute, but first, know that the Government of Canada is paying close attention, with many web pages under its various department portals dedicated to explanations of this emerging disease issue and threat factors for everyone from farmers to health-care workers to the general public. The information is solid, science-rooted and offered so that people can make informed decisions about their own risks of exposure.

Although avian influenza mainly affects birds, it sometimes infects mammals, including humans.

Although avian influenza mainly affects birds, it sometimes infects mammals, including humans. As with many diseases, some birds that become infected fall ill and die while others appear healthy. The numerous types of avian influenza are all caused by strains of type A influenza. Some, such as A(H5N1) and A(H7N9)—classified as Highly Pathogenic Avian Influenza (HPAI) based on the severity of illness in birds—have also caused serious illness in humans; as of June 2024, there have been 900 human cases globally with a mortality rate of 52 per cent. Though it’s worth noting this may be an overestimate given mild infections can go undetected, still… Fifty. Two. Per cent. That makes COVID’s 1.4 per cent mortality rate seem like diaper rash.

Although the World Health Organization maintains that the likelihood of sustained human-to-human transmission remains low, we’ve heard such things before. Influenza viruses mutate like mofos and have already ripped through many groups of birds and mammals to which they weren’t previously well adapted. So, there’s that.

Human cases can occur through direct contact with infected birds (dead or alive) or contaminated environments. For instance, infection has been reported after defeathering of dead H5N1-infected swans (the virus can survive in feathers for more than five months). And while it’s “thought to be possible” (meaning only a matter of time), to date there are no documented cases of humans contracting the virus from a mammalian pet despite increasing reports of mammal-to-mammal transmission and spillover from infected livestock (numerous human cases in the U.S. were contracted from dairy cattle).

Mutations within some Eurasian/North American strains of the virus show enhanced replication in mammalian cells, evasion of immune response, and increased virulence (remember COVID19’s Omicron and Delta variants?). As well, pathogenicity and transmissibility studies indicate these emerging strains indeed cause more severe illness, and—let’s call this worse—that some common flies and beetles can act as mechanical transmitters of H5N1 and other avian viruses. Uh oh.

How did this mess start? Pretty routinely: Arising in Asia in 2020, it travelled to Europe with migrating birds and into poultry flocks, millions of which were culled. Then the story got stranger. The virus moved into seabirds and on to sea mammals. In North America, its arrival was off the radar. In December 2021, while we were all in the throes of our own pandemic, bird flu turned up on a farm outside St. John’s, Newfoundland. Hundreds of farm birds died, and the rest were culled. But culling doesn’t matter for wild birds, which died in droves across the country.

There have been 900 human cases globally with a mortality rate of 52 per cent. That makes COVID’s 1.4 per cent mortality rate seem like diaper rash.

The jump from seabirds to sea mammals was the eye-opener. In October 2023, the virus killed 17,400 elephant seal pups in Argentina—95 per cent of the colony’s young—and some 24,000 South American sea lions; in the U.S. alone, 90 million birds were culled in a failed attempt to stop a virus that was now simultaneously killing mammals (in Eastern Canada as well) from squirrels to raccoons, foxes to skunks and dolphins to polar bears before infiltrating livestock for the first time by jumping to dairy cows. Virologists have never seen anything like it.

We’re told that HPAIs aren’t a food-safety concern, largely because pasteurization (milk) and cooking (eggs, poultry, beef) tend to kill and disassemble viruses. Indeed, every meat and dairy product we currently eat is already swimming in viruses and bacteria like Salmonella and E. coli that require proper handling. But if you choose to eat raw, look out. A recent study confirms high virus-level infections in rodents fed H5N1-contaminated raw milk. In a June 2024 update, the USDA Animal and Plant Health Inspection Service reported 36 more H5N1 detections in wild house mice in the same New Mexico county, as well as four in local domestic cats (which eat mice and birds). WastewaterSCAN, a national monitoring system based at Stanford University, launched an H5N1 avian influenza wastewater dashboard that now shows detections at about a dozen locations.

Is H5N1 coming for us? Is it really only a matter of time before it mutates enough to not just jump into humans, but move between us? Epidemiologists think so. Finland was the first country to offer avian influenza vaccines to poultry farmers, veterinarians, scientists and people who work on fur farms (mink are highly susceptible). In June, the U.S. contracted for millions of H5N1 flu vaccine doses to add to its stockpile, and the EU likewise planned to make 40 million doses for 15 countries. Beyond a dedicated vaccine, having had a number of different seasonal influenza vaccinations might also confer some level of immunity to H5N1. But for now, I suggest we all pay closer attention to a situation that is not only fast-evolving, but unprecedented in the annals of global disease.

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