H5N2 Bird Flu Explained—What To Know As First Human Death Confirmed
Understanding the H5N2 Virus and Its Implications
The World Health Organization (WHO) recently reported the first confirmed human case of H5N2 bird flu in a 59-year-old man in Mexico, who died in April. This case has heightened concerns about the potential spread of bird flu among humans, especially since the man had no known exposure to poultry or other animals.
Dr. Troy Sutton, an assistant professor at Penn State, explains that exposure to H5 viruses in Mexico is not surprising. These viruses have been present among poultry and wild birds in the region since the mid-1990s. However, unlike other avian influenza strains such as H1 and H3, H5 viruses rarely infect humans.
H5N2, like other bird flu viruses, is classified based on two proteins on its surface: hemagglutinin (H), which helps the virus infect cells, and neuraminidase (N), which aids in spreading the virus. There are nine known subtypes of H5 viruses. H5N1, a related strain, has caused significant outbreaks in poultry and occasional human infections but is not commonly transmitted from person to person.
The patient in Mexico developed symptoms, including fever, nausea, diarrhea, and shortness of breath, about a week before his hospitalization and subsequent death on April 24. WHO noted that the man had multiple underlying health conditions, likely worsening his infection. During the investigation, no other cases were reported, and only one of the 17 hospital contacts showed mild symptoms.
Experts are particularly concerned because the man had no direct contact with poultry or other animals, raising questions about how he contracted the virus. If he was infected by another person, it could indicate additional undetected cases. Dr. Michael Osterholm, an infectious disease expert at the University of Minnesota, believes human-to-human transmission is unlikely, suggesting the man and any potential cases likely contracted the virus from the same source.
The H5N2 virus that infected the man is considered low pathogenic, meaning it is less likely to cause severe illness. High pathogenic strains have genetic changes that make them more dangerous, while low pathogenic strains often infect various animal species with minimal symptoms. Despite the low pathogenic nature of this H5N2 virus, the possibility of it mutating and spreading to humans remains a concern.
Dr. Paul Offit, an infectious disease expert at Children’s Hospital of Philadelphia, highlights the need for further genetic sequencing of the H5N2 virus to determine its potential risk to humans. He notes that H5 viruses generally struggle to infect humans because the cell receptors they target in birds differ significantly from those in humans. This is why human infections usually result from direct contact with infected birds rather than human-to-human transmission.
H5N1, which has caused infections in humans since 1997, has never led to widespread human transmission. According to Offit, H5N2 does not appear to pose a significant pandemic threat. If the virus cannot reproduce well in the upper respiratory tract, it cannot spread easily between humans.
Dr. Sutton emphasizes the importance of ongoing genetic research to understand the H5N2 virus fully. Until more information is available, drawing definitive conclusions about its threat to human health is challenging.
Osterholm advises that H5N1 remains the primary concern, particularly as it has infected dairy cows in the U.S., raising fears of mutations that could enable human transmission. As scientists continue to monitor and study these viruses, vigilance and preventive measures are crucial to mitigate the risks of avian influenza.
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