SARS-CoV-2 was not the first corona virus to cause fear of a pandemic. There were concerns about SARS and MERS before it arrived. Influenza viruses are also a regular source of worry, as they can often spread to us from farm animals. Earlier this week, a report was published describing an influenza virus that the researchers identified it identified as "pandemic potential". The virus is currently jumping from farm animals to us, but is currently unable to spread between humans.
The institutions to which some of these researchers are affiliated – the key laboratory for animal epidemiology and zoonosis, the Chinese National Influenza Center and the Center for Influenza Research and Early Warning – provide evidence of how seriously China has taken the risk of the newly developed influenza strain .
For seven years, these centers helped researchers do something that made everything you did for your thesis feel comfortable: removing pigs' nasal swabs. Almost 30,000 of these swabs came from random pigs that appeared in slaughterhouses, and another 1,000 from pigs that were brought to the veterinary's office with breathing problems. Why pigs? For one, some historical pandemics named after their origin are called swine flu. And there is a reason for this: pigs are known to be infected with influenza viruses that are native to other pigs, birds and us humans – to whom they are often in close proximity.
All of these were checked for the presence of influenza viruses and some of the viruses were subjected to full genome sequencing. The good news is that influenza viruses are not widespread in China's agricultural system. Only 0.45 percent of the randomly selected pigs carried an influenza virus. Among those who were brought to the vet for breathing problems, the percentage was not even particularly high: 4.23 percent. So influenza is a relatively small but constant feature in the Chinese agricultural system.
There are many strains of influenza viruses that can be distinguished by specific features in the sequences of their genome. And because of a peculiarity of the influenza genome, most viruses consist of a complicated mixture of these viruses. Like the human genome, it is not a single molecule. Instead, the genes of the influenza virus are spread across eight different RNA molecules. If a single cell is infected with more than one virus, these eight segments are randomly mixed in each virus produced in that cell. The typical virus that the researchers found consisted of parts of more than one well-characterized virus.
Given the eight-year surveillance, researchers were able to track changes in the viruses that circulated among China's pigs. And over time, there was a clear trend: a virus that we'll call G4 (short for G4 EA H1N1) dominated the swine virus population in the later years of the study. It consists of parts from three different strains of influenza that have been described above, but is largely based on an avian virus isolated in Europe.
Since this is a surveillance project, the researchers were naturally curious whether the virus could pose a threat to humans. And the answer is worryingly yes. The parent line of the virus was already known to interact with human cells, and the researchers confirmed that it can infect human respiratory cells grown in a culture dish. Ferrets are widely used as a model for the spread of the influenza virus, and this virus has been able to infect ferrets either through direct contact or through breath droplets. That means the potential to infect people in the real world is there.
Next, the researchers turned to the real people. They viewed the blood plasma of hundreds of farm workers with members of non-agricultural households as controls. The bad news: Over 10 percent of farm workers had antibodies that could recognize this virus, and the number increased over time. The virus had spread to some members of the general population. The good news is that everyone infected there had close contact with pigs, either near a farm or in food processing. There is no evidence that the virus is spreading between people at this point.
Now it is possible that these people come into contact with another, but closely related virus and thus produce antibodies that mutually recognize the swine virus. That would be worrying in its own way, of course.
So is it time to panic about it? The answer is clearly no – there is currently no evidence that the virus spreads to humans. It has the potential to trigger a pandemic, but this potential is definitely not being realized at this point. But it is precisely for this reason that we primarily have such monitoring programs. Current flu vaccines would not protect against this virus, and it is definitely something that we want to keep an eye on. Hopefully China and its international health partners can keep an overview.
PNAS, 2020. DOI: 10.1073 / pnas.1921186117 (About DOIs).