Top virologist explains: Can bird flu among humans become like Covid or long Covid?

Two unusual bird flu infections among humans were reported recently — one from Mexico, where a new strand infected a person, and the other from India’s West Bengal where a known viral strand infected a child. While the Mexican patient died of bird flu, the Indian child survived the infection.

Against the backdrop of the COVID-19 pandemic that brought the world to its knees and amid predictions that a bigger viral pandemic may strike the globe anytime, the bird flu cases have left many wondering if this could be the next public health threat. We spoke to India’s top virologist Dr Shahid Jameel to understand the threat the bird flu viruses may pose to humans. Excerpts:

How does bird flu spread to humans? Is consuming poultry products a common way of getting infected?

Consuming poultry is not usually a common way of getting infected because we cook the meat before eating. So in case the product is infected with the virus, it gets killed very quickly.

However, people selling poultry, people preparing the bird and also people who are in poultry farming and very close contact with lots of birds are primarily vulnerable. India’s domestic poultry is simply a carrier of the bird flu virus as of now.

 The virus is endemic largely in migratory birds. But then you know when birds migrate they do leave their droppings and that’s how domestic poultry gets infected. The transmission to humans of the bird flu virus is very rare and difficult.

Having said that, there are two kinds of influenza viruses that transmit easily to humans. While the bird flu virus transmits largely among bird populations, the human flu virus can circulate among pigs too.  

 Pigs are a species that can get infected easily by both human and bird flu viruses and that’s why they are sometimes called mixing vessels for these viruses. So, if a pig is co-infected at the same time by a human and a bird virus then those viruses can exchange their genetic elements as a result of which a hybrid virus emerges.

 Sometimes those hybrid viruses can be transmitted easily to humans. And that’s why you have large outbreaks.

A bird flu case was reported recently from West Bengal, where the patient was infected with the H9N2 strain. Also, the world’s first case of H2N2 strain in a human was reported from Mexico. This comes while the most common strain infecting humans remains the H5N1 virus. How different are the new ones and are they more dangerous?

The reason why this happens goes back to the structure of the bird flu and the human flu viruses. The kind of elements that the human flu virus uses to attach itself and get into human cells is largely present in the upper respiratory tract. And that’s why the common flu symptoms you get are largely concentrated in your nose and throat. Chances are very rare that they transform into lung infections.

The reason for this is that the human flu virus largely enters cells in our upper respiratory tract. It doesn’t enter our lower respiratory tract cells or lung cells very easily.

On the other hand, the bird flu virus is such that it can enter lung cells fairly easily and once somebody gets infected the virus moves into the lungs easily. So that’s why the disease is rare but it is severe. It depends on both the immune system as well as certain proteins present on the surface of our cells.

Does the immune system play a role in who gets infected and who does not?
Yes, the immune system plays a role because it is exposed to human viruses. Therefore, we have a lot of natural immunity. But if a new human virus is circulating that season, lots of people get it.

But then the infection remains fairly mild. You have a cough and cold for a few days and then you get over it. It doesn’t become pneumonia.

On the other hand, if the bird flu virus can get to the lungs, it multiplies quite rapidly there and one may get pneumonia.  

Is there an explanation for why a new strain of bird flu has started infecting humans?

Every virus changes in time and there are multiple pathways for that change. Influenza viruses are particularly easy to change because of the way the genetic elements of these viruses are designed.

So there are two alphabets H and N in the name of the strain where H refers to a protein on the surface of the virus which is called hemagglutinin and N refers to another protein on the surface of the virus which is called neuraminidase. And the virus essentially uses these two proteins to enter our cells or the cells of any species that it infects.

So H5 viruses are bird flu viruses. They infect the H5 type of hemagglutinin and bind better to bird cells whereas the H3 or the H1 type binds better to human cells.

Some of these viruses enter birds better than human cells. So the virus is changing quite rapidly and there are a lot of reports now of cattle getting infected with bird flu viruses. Now cattle sort of fall in the same category as humans in terms of how they respond to bird flu.

Cattle getting infected with the bird flu virus is telling us that the virus is adapting to mammals. And if it is adapting to mammals then it becomes easier for it to transmit to humans in the future.

What we don’t know is whether the ease of transmission of a bird flu virus into mammals will reduce its ability to cause severe diseases in mammals. But it should be a cause of concern that the virus globally is adapting to mammals.

Do we have a vaccine that can act against bird flu? The Covid-19 vaccine was manufactured in a record time. So in case bird flu becomes an epidemic how quickly can we produce a vaccine?

Well, I mean a vaccine for flu is already there. People do use it. So human flu viruses every year you get a different vaccine that is put out by the WHO (World Health Organization).

It’s a constant surveillance programme globally. And based on that we can predict which human flu viruses are going to circulate in the population in the next season. And a vaccine for that is prepared in advance and given.

In India, that vaccine comes in August every year. It’s another matter that most people don’t take the vaccine. But it’s a good vaccine. People should be taking that vaccine. So to answer your question, yes there is already a vaccine for the human flu viruses. And you know it’s the same process to make a bird flu vaccine.

Do you think bird flu infections can affect adults and children differently? Are there particular population groups that are more vulnerable to bird flu?

See, what happens is as you become older you get a lot of exposure to all kinds of flu viruses. And the older you are the more exposure you have to these viruses in your life. And therefore you develop a very broad range of immunity.  

It’s another matter that the elderly also become more susceptible because as we age our immune systems also become weaker. So if you compare let’s say a four-year-old child to let’s say a 30-year-old or a 40-year-old, the four-year-old child has had very little exposure to the environment as compared to a 40-year-old.

So a 40-year-old’s immune system controls the virus much better than a four-year-old’s immune system. So children are generally more susceptible to these respiratory viruses because of that reason.

A majority of human cases of bird flu infections have been fatal. Is there a possibility that it might affect the survivors something like long Covid?

No, that doesn’t happen with flu viruses. There’s a lot of experience with flu viruses. I mean every season we get flu viruses.

So there’s nothing like a long flu. And also people react differently to the same virus. I mean the way you and I would react to a flu virus would be very different.

And that also depends on various host factors that we have. Various experiences that we have had with other viruses including flu viruses. That’s common.