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The other bird flu: H5N2

UTSA Professor of Microbiology and Associate Director of The South Texas Center for Emerging Infectious Diseases, Jose Lopez-Ribot, holds a Petri Dish full of growing fungi.
Ari Castaneda
University of Texas at San Antonio
UTSA Professor of Microbiology and Associate Director of The South Texas Center for Emerging Infectious Diseases, Jose Lopez-Ribot, holds a Petri Dish full of growing fungi.

On June 5, we learned that a man in Mexico City had died of avian influenza. He became symptomatic back in April, and Mexico reported his illness to the World Health Organization in May. However, the patient was not infected with the strain of bird flu we've been watching move around the globe, killing birds and mammals and threatening the human population. That strain of bird flu is H5N1. The strain in Mexico City was H5N2.

What is the difference, and what does this mean in the context of the broader bird flu surveillance?

TPR's Bonnie Petrie asked Texas Biomedical Research Institute virus expert and vaccine researcher Luis Martinez-Sobridoabout H5N2.

This interview has been edited for length and clarity

Petrie: What is H5N2?

Martinez-Sobrido: H5N2 is a subtype of influenza A virus that has been circulating in farms in Mexico for years. Two types of H5N2 avian influenza viruses have been identified: high pathogenic and low pathogenic H5N2 influenza viruses. However, no human cases of H5N2 has been reported until this recent case of avian H5N2 influenza virus in April 2024; it is unclear if there is a link between this human case and cases of high or low pathogenic avian H5N2 in farms.

Petrie: What does this mean in the context of the growing zoonotic pandemic of H5N1? The man in Mexico City apparently had no contact with cows or poultry and none of his known contacts are positive for flu on PCR tests, though experts are still waiting for the results of blood tests, according to W.H.O.

Martinez-Sobrido: That's correct. This lethal human case of avian H5N2 corresponds to a person with no history of exposure to poultry or other animals. It will be important to know how this person was infected with the H5N2 avian influenza virus. Importantly, testing of people identified to be in contact with this patient have tested negative for H5N2 avian influenza by genetic analysis. This suggests that the virus is not easily transmitted between humans, similar to the situation with the recent human H5N1 cases in the US.

Petrie: What are we to make of that?

Martinez-Sobrido: This is the first laboratory-confirmed human case of infection with an avian H5N2 influenza virus reported and the first case of an avian H5 virus infection in a person in Mexico. Based on current information, and similar to the cases of avian H5N1 in the US, the WHO assesses the current risk of avian H5N2 to humans to be low. That being said, and because of the number of H5N1 and H5N2 cases identified, travelers to countries with known outbreaks should avoid farms or being in contact with farm animals/animals in live animal markets until we have a better understanding on the situation with these avian H5N1 and H5N2 influenza viruses.

Petrie: Is Texas Biomed working with H5N2?

Martinez-Sobrido: No, currently we are not doing any research on avian H5N2 influenza viruses at Texas Biomed.

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