What to know about the first human case of H5N2 bird flu

Is there a new strain of bird flu we should be worried about?

On Wednesday, the World Health Organization reported the first confirmed human case of the H5N2 type of bird flu in a 59-year-old man in Mexico who died in April.

The case adds to growing anxiety about the risk of bird flu spreading among people, especially since the man had no history of exposure to birds or other animals, according to the WHO.

The strain is different from the bird flu virus outbreak, called H5N1that circulates among herds of dairy cows in the United States and has caused mild infection among three agricultural workers.

What is H5N2?

H5N2 is just one of several types of bird flu viruses. Does this really pose a significant health risk to humans?

Exposure to the H5 virus in Mexico is not surprising, said Dr. Troy Sutton, assistant professor of veterinary and biomedical sciences at Penn State. H5 viruses have been circulating among domestic and wild birds in Mexico since the mid-1990s. However, unlike other strains of bird flu that have caused outbreaks in humans – such as the H1 and H3 viruses – H5 viruses rarely infect humans.

Viruses are classified based on two types of proteins on their surfaces: hemagglutinin, or H, which plays a crucial role in allowing the virus to infect cells, and neuraminidase, or N, which helps the virus spread. Many different combinations of H and N proteins are possible.

H5N2 belongs to a family of bird flu viruses called H5, which mainly infects wild birds. There are a total of nine known subtypes of H5 viruses, according to the Centers for Disease Control and Prevention.

H5N1, detected in US dairy cows in March, also belongs to this family. It is commonly associated with highly contagious strains of the H5 virus called the “Guangdong Goose lineage,” which have caused numerous outbreaks in birds over the past 20 years and sporadic infections in humans, Sutton said.

H5N1 has infected people in 23 countries since 1997, according to the CDC, resulting in severe pneumonia and death in about 50% of cases.

“They are a separate lineage, with a separate history and a separate kind of history around the disease that they cause,” Sutton said of the H5N2 and H5N1 viruses.

Should people be worried?

The patient in Mexico was bedridden for several weeks before developing symptoms.

According to the WHO, on April 17 the man developed fever, nausea, diarrhea, shortness of breath and general malaise. A week later, on April 24, he was hospitalized and died that day.

Sutton said it’s important to note that the man had several underlying medication issues, which likely exacerbated his infection.

“The person may already be quite sick,” Sutton said. “That changes the calculus a little more than, say, a healthy farm worker getting infected.”

The WHO said no other cases were reported during its investigation. Of the 17 contacts identified and followed up at the hospital where the patient died, one reported a runny nose.

However, experts still do not know how the man became infected with the virus, as he was not exposed to birds or other animals. If he was infected by another human, this suggests there could be additional unidentified cases.

“It is concerning that a new subtype of virus has infected a human,” Sutton said.

Dr. Michael Osterholm, an infectious disease expert at the University of Minnesota, said human-to-human transmission is unlikely. “They probably got it from the same place.”

The data shows that the H5N2 virus that infected the man is a low-pathogenic virus, meaning it is unlikely to cause serious illness, Osterholm said.

“There is the higher path and the lower path, and the higher path has certain genetic changes. This makes it much more likely to cause serious illness,” Osterholm said. “And the low route, easily transmitted, can often infect any number of animal species with few or no symptoms.”

What scientists want to know

Paul Offit, an infectious disease expert and director of the Vaccine Education Center at Children’s Hospital of Philadelphia, said the main question among experts is whether H5N2 mutated in a way that made it easier to spread to humans.

H5 viruses in general, he said, struggle to infect people because the cellular receptors they target in birds are very different from ours.

That’s why often, he said, people become infected with the H5 virus through direct contact with birds and birds, rather than with other humans.

H5N1, which evolved to cause rare infections in humans, has never caused widespread transmission between humans, he added.

“The fact that it is H5N2, compared to H5N1, I don’t think is significant in terms of representing something that is more likely to be associated with a pandemic,” Offit said. “If the virus cannot reproduce well in the upper respiratory tract, it will not be able to spread easily from human to human.”

Sutton said scientists still need to perform more genetic sequencing of the H5N2 virus that infected the Mexican man before they will be able to determine whether it is a risk to humans.

“Until we have that information, it’s really difficult to draw many conclusions.”

Osterholm said H5N1 is really the one we need to be “laser focused on.”

The H5N1 virus took off in dairy cows in the U.S., infecting at least 84 herds in nine states, according to the US Department of Agricultureraising the possibility that it could acquire mutations that allow it to spread in humans.

This article was originally published in NBCNews. with