Bird flu in humans in the US: Here’s all you need to know

What is H5N1?

H5N1 is a type of influenza virus that causes severe respiratory disease in birds but has occasionally been known to jump to humans as well. While the infection has not been easily transmissible in humans so far, the mortality could be as high as 60 per cent when it does. To compare, the mortality rate of Covid-19 was around three per cent even with the most virulent variants.

What do we know of the cases in the US so far?

The specimens from the Texan person and cattle was confirmed to be the highly pathogenic avian influenza A (H5N1), which retained its avian genetic characteristics, and “for the most part lack changes that would make them better adapted to infect mammals,” said the US Centers for Disease Control and Prevention (CDC).

The human specimen, however, did have one mutation, PB2 E627K, which is known to be associated with a virus adapting to mammalian hosts.

Have there been cases in humans before?

Human infections with H5N1 were first reported in 1997 during a poultry outbreak in Hong Kong. Human cases have mostly been reported from Asia, with some cases from Africa, Americas, and Europe. Almost all these cases have been in people who were in close contact with infected birds. Experts say that a person would need to breathe in a large amount of the virus to develop a respiratory complication. There have been 887 cases of H5N1 between 2003 and 2024, of which 462 people died, according to data from the World Health Organisation (WHO). This pegs the case fatality ratio — proportion of deaths among diagnosed cases — at 52 per cent.

In fact, India reported its first case and death due to H5N1 in 2021. The 11-year-old boy died of respiratory failure at the All India Institute of Medical Sciences in Delhi.

What are signs and symptoms?
According to the CDC, signs have ranged from mild illness, manifested through eye redness (conjunctivitis) or mild flu-like upper respiratory symptoms, to severe (such as pneumonia requiring hospitalisation). Sometimes you may not have a fever at all. At other times, you could have a temperature of 100 F, cough, sore throat, runny or stuff nose, muscle or body aches, headaches, fatigue, and shortness of breath or difficulty breathing. Less common signs and symptoms include diarrhoea, nausea, vomitting or seizures.

What about treatment?

In humans, the antiviral Oseltamivir can be administered early in the course of the disease. Respiratory symptoms need to be managed in a hospital ICU. There are also vaccine candidates that have been developed, but not readily available, for H5N1.

Is it safe to eat chicken?

Yes. First, the current outbreak has been reported from the US. Second, even when there is a bird flu outbreak in India, properly cooking the chicken at high temperatures kills the pathogen and makes it fit for consumption.

Can it cause the next pandemic?

Dr Sreekumar said the first priority was to prevent further spread — Other people with symptoms in the area have to be tested, contacts have to be tested, and the person has to remain in isolation to prevent further spread. “One case is not enough to say that the infection can cause a pandemic. It is too early. However, it is important to keep an eye on the pathogen for changes that can make it more transmissible,” he added.

Avian influenza is not on the WHO priority list of pathogens of pandemic potential.