‘We have to be very cautious’: Experts speak out on dangers of avian flu outbreak

This is a very difficult question. On one hand, we should be very concerned. But on the other hand, this is not something that’s happening now or even happening imminently.

What we need to be concerned about right now is the fact that there is a lot of H5N1 spreading within the wild bird and farmed poultry populations. This has been occurring since 2021 and it is very hard to get this virus out of the wild, migratory bird population.

We also need to be concerned about the fact that the U.S. has seen an uncontrolled outbreak in dairy cattle that has been occurring now for close to a year, possibly longer.

The virus was introduced to cows from a wild bird source and has now spread throughout the U.S, but we still don’t have a good idea of the scale and scope of it. This is concerning because as long as we don’t have an effective plan to contain its spread, then we are going to continue to see human populations at risk – particularly dairy farm workers.

We know from a recent CDC study done in partnership with researchers in Colorado and Michigan that about 7 per cent of dairy workers in the study had evidence of prior infection with H5N1. That is something to be concerned about for the future because the more the virus infects humans, the more the virus can overcome the barriers it needs to become a pandemic-level virus.

When that might happen, we can’t really predict. The good news is we haven’t seen human-to-human transmission yet, but that doesn’t mean that we have nothing to worry about.

We still don’t know exactly how bad an H5N1 pandemic might be.

We still don’t know exactly how bad an H5N1 pandemic might be. This is in part because we don’t really know what that would look like in terms of mortality and morbidity on a global scale. What we do know is that historically, H5N1 has a case fatality rate of about 50 per cent, although that number is debated because we’ve likely missed cases in humans that weren’t clinically as serious. Even if it’s not a 50 per cent fatality rate, it has the potential to be much more destructive (and much more expensive to the global economy) than the COVID-19 pandemic.

In the most vulnerable populations with no vaccines or population immunity, the SARS-CoV-2 virus has a mortality rate of about three per cent. Even if H5N1 is only at, say, a 10 or even five per cent mortality rate, that would still mean millions of more people dead compared to COVID-19. It also has the potential to be very destructive in terms of food security.

We need to increase active surveillance programs for influenza-like illnesses. But one of the biggest things we need to do is specifically get the cattle outbreak under control, and to do that we need to increase testing in both humans and cattle.

In terms of personal safety, you shouldn’t be able to contract H5N1 by consuming meat or poultry. But it looks like that may not be the case if you consume unpasteurized or raw milk. There have been a number of cat deaths in particular that have occurred from cats drinking raw milk at dairy parlors. In the U.S. in particular, raw milk is becoming more legal and accessible which is a disturbing trend because we don’t want to find out what human susceptibility is like to H5N1 from raw milk.

The case in B.C. was recently identified as a bird avian flu, not the dairy avian flu, and therefore not associated with the dairy outbreak in the United States. Generally speaking, this is good news. So, am I concerned about it? Of course “yes” for the young person infected but not particularly for the risk of a major outbreak.

There’s a long history here that hasn’t been reflected well in most of what’s being reported. H5N1 viruses have been actively mutating in the long-migrating bird populations for the last 30-plus years, since they were found in Southern China in 1997. In that time, there have been sporadic cases of human infection with these types of viruses.

Everyone was really worried about them initially, so worried that China slaughtered 1.6 million local chickens to contain it.

Then two independent studies were published in 2012 that showed that H5N1 viruses only needed a small number of mutations to become transmissible from mammal to mammal by aerosol, and that scared the hell out of everybody back then. Now we’ve got elephant seals dying in Argentina, mink dying in fur farms in Europe and dairy cattle in North America. So, it is pretty clear that at least some of the H5N1 viruses are starting to move towards mammals. But so far, no strain has shown the ability to be readily transmitted from human to human.

30 years of waiting for something bad to happen has sort of dulled that sense of urgency.

Right now in B.C., there’s lots of H5N1 in wild bird populations and plenty of evidence of transmission from wild birds to domestic flocks. We are in a world where H5N1 viruses are not that far away from a potentially really bad outcome.

However, that potentially dangerous recombination event hasn’t happened yet. So, am I generally concerned that something bad might happen with H5N1 viruses? Yes. But at some level, 30 years of waiting for something bad to happen has sort of dulled that sense of urgency.

Every time the public starts focusing on these kinds of risks, it’s an opportunity to make sure that we are better prepared for whenever that recombination event does happen. We didn’t do brilliantly with SARS-CoV-2, so hopefully we will do better next time.

To paraphrase a colleague when asked “How worried should we be about H5N1?,” the answer is somewhere between zero and 100 per cent. The current situation is concerning given the scale of mammal-to-mammal transmission and speed of viral evolution. As more H5N1 circulates in mammals such as cattle in the United States, there are more opportunities for the virus to evolve in ways that could cause a human outbreak.

The recent B.C. case adds to the concern, as it is a severe infection and is caused by a different type of H5N1 virus than the cattle outbreak. This virus was independently introduced to North America before reassorting (i.e., mixing up its genome) with other local avian influenza viruses. Preliminary analyses of this virus show that it has some changes that may make it more capable of infecting humans. A close relative of this virus was also recently detected in Oregon pigs. As pigs can be infected by both human and avian influenza viruses, they can generate new hybrid viruses that are more transmissible in humans. Cases in multiple mammal species caused by multiple variants means that there may be multiple, unpredictable evolutionary routes to a potential pandemic.

It is vital to support on-going efforts to reduce the spread of these rapidly evolving viruses.

Therefore, it is vital to support on-going efforts to reduce the spread of these rapidly evolving viruses. Targeting these interventions requires high quality data drawn from genome sequencing, lab virology and human and animal surveillance systems. Due to H5N1’s complex spread across wildlife, livestock and humans, this involves bringing together multiple different sectors, government agencies and academic disciplines. Fortunately, drawing on lessons learned during the COVID-19 pandemic, Canada has several One Health initiatives that support exactly this type of multidisciplinary work.

The highly pathogenic avian influenza H5N1 is now spreading quickly in avian species. The virus has also spilled over to wild animals, dairy cattle and, occasionally, humans. Because we have seen this virus circulating so much, and the virus is so well known for its ability to mutate and adapt, we have to be very cautious. That said, I don’t want to spread panic.

For now, it seems like this virus has not acquired the mutations and abilities it needs to spread between humans. But we have to keep in mind that this virus can jump between hosts of different species.

This virus can jump between hosts of different species.

The reason it has yet to spread from human to human even though humans can become infected from infected animals is that there are some restricting factors to viral replication. The virus has to bind to the host first, so if you look at human infection, the avian virus has to find receptors to bind to in the human respiratory tract. If a virus makes its way to enter the cells, the virus must also acquire the ability to replicate efficiently in the host cells and that is another barrier for the virus to overcome. Our body can also restrict a virus from replicating through our immune systems. Immune systems mount antiviral responses to suppress viral infection. So far, the virus has not figured out how to bypass these barriers in humans.

Farmers and agricultural workers should be very cautious and use proper personal protective equipment when they work with animals that might be infected. People should also stay away from dead birds. Influenza is unique in that it can infect so many species, so we need to be cautious and know that it’s always there.