Bird flu detected in pigs – here's why virologists are concerned

H5N1 influenza is currently detected in pigs. This has been a concern of virologists since the beginning of this highly pathogenic avian influenza epidemic. Rapidly expanding globally in 2020. But why were we especially concerned about pigs? And will this case, discovered on an Oregon farm on October 29, change anything?

It may seem strange that we care about it at all. In many ways, the first reports of this incident come against the backdrop of ongoing virus outbreaks that have devastated seabird colonies around the world. mass death of sea lions And it has led to the emergence of a completely new disease that is completely harmless to U.S. dairy cows.

What we now know is that H5N1 avian influenza infected poultry on small nonprofit farms in the United States, which is now sadly very common. In this case, there were also other animals on the farm, including five pigs. The pigs looked healthy, but nasal swab H5N1 was detected in one of them.

It is not yet known whether the pig was actually infected or simply inhaled the contaminant from the bird. At this time, this particular outbreak does not appear to have spread to other pigs.

Also, “spillover” infections on farms, where one species of virus infects another, is not new. Back in May, H5N1 was confirmed in farmed alpacas. somewhat similar incident.

To understand why pigs have attracted the attention of virologists, we need to consider what it means for a virus to jump from one host species to another. If you think about it for a moment, you'll realize that it's incredibly difficult for viruses to change host species.

The world is full of viruses that infect every species around us. If it weren't nearly impossible for viruses to jump from one species to another, we would be dealing with a new pandemic every 10 minutes.

much more subtle

The reason it's so difficult for viruses to jump between different types of hosts is that viruses are fundamentally different from bacteria and parasites, pathogens that basically just try to eat us. Viruses are more sophisticated.

Viruses work by controlling our cells and carefully reprogramming them into machines that produce more viruses. So a virus that infects a new host species is like trying to win an argument by yelling at people in a language they don't understand. And here comes the pig.

Influenza viruses (especially influenza A viruses, the group to which H5N1 belongs) are unusually good at hybridizing between different host species. They still produce a new human disease only once every few decades, but this is a higher rate of success than any other virus.

In retrospect, most of the pandemics we know about are caused by influenza viruses, and the threat of new pandemics is currently the biggest concern we have regarding H5N1.

One of the main reasons influenza is so good at learning the language of new host species is that if two influenza viruses can invade the same cell at the same time, they can assemble a new virus that takes some of the genes from one parent. It's from. This includes viruses and other viruses. The new viruses created by this can suddenly shift toward evolving better to suit their hosts.

For example, it could look like a bird virus to which we have no immunity, even though we replaced most of its genes with a version that is much better at winning arguments with human cells. This is a powerful way for viruses to cause pandemics. But it only works if the bird virus and human virus can enter the same cells at the same time, and it turns out that this is very difficult for the influenza virus to do.

This is difficult because the influenza virus enters cells by grabbing a specific type of sugar molecule that coats the cell surface. This molecule can be chemically assembled into several different shapes, but one shape of the molecule is used in bird cells (and we currently think that cow udder), a different shape is used in the cells of the human airways.

mixing container

Avian influenza viruses and human influenza viruses try to enter cells by rattling different door handles, which limits the ability of the viruses to meet within the same cell. This is where the pig comes into play. Because it turns out that cells in pig airways use both types of cells. sugar molecules on the surface. Pigs are susceptible because pig cells can be infected with both avian influenza and human influenza. “Mixing container” Influenza viruses with pandemic potential could be brewed there.

Has this happened yet? Thankfully, no. At this time, this detection of H5N1 in pigs appears to be an isolated incident. We don't know how likely it is to happen again.

In fact, there is support for the hypothesis that this particular virus may be very difficult to infect pigs. By some work Additionally, the observation is that this is the first suspected H5N1 infection in pigs, despite the spread of H5N1 in the past four years and outbreaks in all kinds of animals.

Even if H5N1 were to succeed in establishing persistent infections in pigs, as has already happened in cattle, what that would mean is by no means certain. we know the influenza virus May mix with each other in pigsHowever, we also know that the strain of influenza virus that entered pigs in 1918 has since spread among pigs. over 90 years before combining with other viruses to cause the 2009 swine flu pandemic.

So why have reports of H5N1 in pigs garnered so much attention from virologists? H5N1 can be a very dangerous virus to a variety of animals, and when its genes combine with the human virus, , which could become even more dangerous for us.

The risk is already starting to rise as this year's winter flu season begins for humans, with the H5N1 virus circulating on U.S. farms. The suggestion that this virus could emerge in animals and mix and adapt with human influenza is a troubling reminder that the capabilities of H5N1 viruses can change rapidly.

When it comes to which animals to look out for for signs that such changes are occurring, some animals are more even-keeled than others. As long as H5N1 exists, virologists will be watching pig infections with interest.