Scary-sounding new virus in the news? These are the questions you should ask

In the United States, a dairy farm worker develops itchy, bloodshot eyes. In Australia, a young girl falls ill after a vacation abroad and is hospitalized. In Mexico, another man, already sick and bedridden, becomes seriously ill and dies. Each of these recent cases was caused by a different strain of the flu virus. In each case, it was an animal virus that should not normally occur in humans at all. Should such stories worry us?

When stories like this hit the news (and they do quite often with flu viruses), journalists write to virologists and ask: How worried are you about this?

The honest answer is that a virologist's opinion of a story depends on many things, including our personalities: some of us are naturally optimistic, while others are more inclined to catastrophize. But our professional backgrounds give us an idea of ​​what to look for in a news story about a novel virus. The next time you read about a novel virus in the news yourself, these questions can help you decide how worrisome it might be.

How far has it come?

This is usually the first question. It is actually very difficult for a virus to adapt to a new host animal and thrive. Even influenza viruses – which are basically bird viruses, but are notorious for causing repeated pandemics in humans – only manage to do this every few decades.

For a virus, transmission from another animal host to humans is a step-by-step process. (I write “humans,” but the logic is the same if you're worried about a virus jumping between any two host species, such as when bird flu adapts and spreads to cattle.)

Have people been exposed to the new virus and developed an immune response without showing any signs of infection? If there has been a spillover infection from a person (whether or not it caused severe disease), is there any evidence that the virus has adapted sufficiently to spread to other people? And if the virus is now spreading among people, is the spread still at a point where it can be contained?

How much do we know?

Surveillance is hard work that requires resources and collaboration, but it is hugely important for understanding and controlling outbreaks. So what do we look for?

When we test people for their immune responses to a virus (serology), we learn who has been previously exposed to the virus. By sequencing viral genomes (from infected people or from the environment), we learn where the virus is currently located, but we can also find out how it spreads and how it changes.

This is possible because viruses mutate quickly. By comparing the differences in their genetic sequences, we can build family trees ('phylogenetic trees') that help us reconstruct how the virus got to certain places at certain times.

Is it one big outbreak or many individual outbreaks? Family trees can tell us that. By studying the changes in the virus's genome, we can also look for telltale signs that it is adapting to a new species – assuming we understand the virus well enough to figure that out.

What are we dealing with?

The better we understand a virus, the better we can predict what it might do next. For some very well-studied viruses, such as influenza viruses, we know some of the genetic changes that are warning signals of adaptation to a new host species.

What else can we look out for? We are more concerned about viruses jumping between similar host species because it is easier for the virus to do so. A flu that is already in a mammal is more likely to infect us than a bird flu.

We can look at the likely routes of transmission – a respiratory virus is likely to spread more quickly than one transmitted through sexual contact. We can also try to guess at the consequences of infection – viruses that cause severe disease are a concern, but in terms of spread, we are also concerned about less severe cases that could lead to people spreading the virus without realising it.

However, viruses are a delicate matter and their effects are difficult to predict in practice.

The current outbreak of the H5N1 influenza A virus in cattle is a good example of this. The fact that the influenza A virus infected cattle and then spread through milk was a big surprise. And although it is known that H5N1 can cause very serious disease, some cattle appear to carry the virus without becoming seriously ill.

Experimental virology, in which animals and cell cultures are infected and studied under controlled conditions in secure laboratories, can be crucial to understanding the true capabilities of a virus.

Could it get worse?

Viruses have difficulty adapting to humans. Anything that gives viruses the opportunity to adapt is therefore a cause for concern. Sustained outbreaks pose a greater risk than isolated cases.

We are more concerned about viruses in animals that have close contact with humans. The spread of H5N1 in North American cattle is more concerning than the spread of H5N1 in South American elephant seals.

We fear that viruses take shortcuts when adapting. In the case of influenza viruses, this can happen in hosts such as pigs, which can take up several viruses at once and thus exchange parts of their genome with each other.

And we worry when people do things that give viruses a chance to get used to them, like drinking unpasteurized milk in areas where it could carry the H5N1 flu virus.

What would the worst case scenario look like?

What would happen if things actually got worse? Are there already vaccines against this virus or a very similar one? Is there the capacity to produce large quantities of these vaccines and distribute them to large numbers of people? Are there already antiviral drugs? Do we know what is needed to effectively treat the symptoms caused by the virus? In this case at least, it helps to face a virus like the flu, which we have been trying to fight for a long time.

The global spread of a new strain of influenza virus is just one of many viral threats, but the H5N1 strain of the virus has done numerous things recently that give us virologists cause for concern.

While isolated cases can have devastating consequences for those affected, the greater risk to society comes from viruses that spread—and H5N1 flu is currently spreading in both cattle in the U.S. and birds around the world. Importantly, though, it's not doing anything right now that we'd associate with spreading among people.

The current mood among virologists is definitely not the same as it was in, say, February 2020, when it became clear that SARS-CoV-2 was spreading uncontrollably among humans. But bird flu is doing enough worrying things right now to make us pay attention. If we do that, hopefully we can all prevent things from getting much more worrying than they already are.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Ed Hutchinson works for the University of Glasgow and is an unpaid fellow on the board of the European Scientific Working Group on Influenza and other respiratory viruses (ESWI) and a scientific advisor to PinPoint Medical. He has previously received honoraria for his work on a steering group of the Centre for Open Science (Open Practices in Influenza Research; 2021-2022) and on an advisory board for Seqirus (2022). His research group receives funding from the UK Medical Research Council, Engineering and Physical Sciences Research Council and Arts and Humanities Research Council, and the Wellcome Trust.