Health

Bird flu H5N8 can now spread to humans: should we be concerned about another pandemic?

It’s not exactly what we want to hear in all-out Covid-19 pandemic, but the world is full of flu viruses waiting in the wings to strike. And they keep changing unpredictably. One to keep an eye on is H5N8, a bird flu virus. When it struck a large poultry farm in Russia in February, it suddenly turned out to be able to infect people as well. Do we have to worry?

The Russian government acted decisively and quickly: 800,000 chickens were killed, the carcasses were destroyed and the farm cleaned up to stop the possible spread to other chicken farms. Tests revealed the H5N8 strain of bird flu, which is considered very dangerous to both wild and domestic birds. H5N8 is already at home in Asia and is increasingly causing deadly outbreaks in birds in Europe.

In the short period from December 25, 2020 to January 14 this year, more than seven million birds were lost to H5N8 outbreaks in Europe and Asia. In Europe alone, there were 135 outbreaks among poultry and 35 among wild birds. To put the numbers in context, humans consume about 65 billion chickens every year, and it is estimated that the number of chickens in the world is 23 billion at any given time.

Never infected people. Until February.

In fact, H5N8 viruses have already infected poultry in the United States, but the viruses come from a different but related virus line, different from the current H5N8 viruses in Asia and Europe. Flu viruses often combine and mutate in unpredictable ways.

But as harmful as H5N8 is to birds, it had never infected humans. Until February. The Russian health authorities also tested about 200 of the people involved in the clean-up of the farm in Astrakhan, using nasal swabs and later blood tests for antibodies. They reported that H5N8 had first spread to humans. Seven of the workers were found to be infected with the virus, although none of them became ill.

With the world lashing other cats with the coronavirus, that news seemed to fall between the folds. Even when a Russian scientist warned that H5N8 might be on its way to evolve into a virus that could pass not only from bird to human, but also from human to human.

On February 26, the World Health Organization published a report on the incident. But it did not consider the event particularly alarming because the virus did not cause disease in humans, and the report rated the risk of human-to-human transmission as low.

The 0.001 percent

Experts are currently divided about how seriously we should take H5N8. The consensus is that for now we are more concerned about other avian flu viruses such as H5N1 that have already proven dangerous for humans. Another bird flu virus, H7N9, first infected humans in 2013. Since then, there have been more than 1,500 confirmed cases (and more than 600 deaths).

It is always possible that any virus can develop human-to-human transmission and also become more dangerous. But H5N8 should overcome both hurdles. H5 viruses all have the same type of binding capacity to human cells, and it is limited. Flu viruses use a slightly different way of attaching to cells in birds than cells in humans, and being good in one way usually means not being good in another.

By the way, just this week a study was published warning that a new pandemic and the virus that could cause it is most likely unpredictable. Six out of 10 infectious diseases that affect humans are of such origin: they come from animals. The number of viruses in birds and mammals that could potentially jump to humans and make us sick is currently estimated at 800,000. Even after decades of research, scientists suspect that we have discovered barely 0.001 percent of the viruses circulating in living things on our planet.

The perfect storm

We may not know which virus will strike, but we do have some control over the environment in which they can take the step towards a pandemic. Michael Greger, the author of Bird Flu: A Virus of Our Own Hatching, says factory farm conditions create a “perfect storm” for the onset and spread of disease.

“We put thousands of animals in tight sheds the size of a football field, where they lie beak to beak or muzzle to muzzle, subject to stress that paralyzes their immune systems, where the ammonia from their own feces burns their lungs, where there is a lack of it. fresh air and sunlight is… Put all these factors together and you have the perfect breeding ground for an epidemic. ”

To make matters worse, selection for specific genes in poultry (for desirable traits such as large chicken breasts) has made these animals almost genetically identical. This means that a virus can easily spread from animal to animal without encountering genetic variants that could keep it. As it tears through livestock, the virus can become even more virulent. Or, as Greger puts it, “If you really want to create global pandemics, build factory farms.”

The World Health Organization and virologists have been warning for years that most emerging infectious diseases come from animals and that our industrialized farming practices increase the risk of epidemics. “Livestock health is the weakest link in our global health chain,” says a report by the Food and Agriculture Organization of the United Nations.

Recipe for a very virulent virus

Bird flu is caused by viruses and factory farms are the perfect breeding ground for it. This is because the birds in these farms are squeezed close together by the thousands and because they are genetically bred almost identically. That’s a recipe for a very virulent virus to show up and spread quickly.

To explain why, here’s a crash course in zoonotic contamination from the pathogen’s point of view. If you are a pathogen in a host, you don’t want to kill that host too soon before you can get into the next host – otherwise you will cut your own transmission line. The faster you replicate, the more likely you are to kill your host before the next host can arrive.

Deep in the wilderness or on a small farm, you will not regularly encounter hosts as a pathogen, so you should keep your virulence, or damage done to the host, quite low. Otherwise you will soon be without hosts. But if you enter a barn with 15,000 turkeys or 250,000 laying hens, you can just burn through it as a pathogen. There is no limit to how virulent you are. And that’s part of the reason why factory farms are more at risk for zoonotic outbreaks than the wild or small farms.

Pigs are also a cause for concern

As we trade more and more poultry and livestock across international borders, we have added to the danger. Strains of viruses previously isolated on opposite sides of the world can now be recombined. Take the flu. That virus has a segmented genome, so an increase in the rate of recombination means an explosion in terms of the diversity of pathogens that evolve.

The world has already seen a very frightening example of this. Between 1997 and 2006 highly pathogenic strains of H5N1 avian flu were associated with poultry farms in China. 60 percent of people who became infected with H5N1 did not survive. If you’re wondering why H5N1 didn’t become such a global drama as Covid-19: because it mostly infects poultry rather than humans; it was not as good at infecting humans as the coronavirus.

By the way, it’s not just birds we should be concerned about. Pigs are also very effective carriers of viruses. A decade before swine flu hit in 2009, the Nipah virus showed up in Malaysian pig farms. It caused encephalitis (inflammation of the brain) in hundreds of people, and about 40 percent of patients admitted to the hospital did not survive.

(jvdh)

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