WHO Confirms First Fatal Human Case of H5N2 Bird Flu in Mexico

The World Health Organization (WHO) has confirmed the first death from H5N2 bird flu in Mexico, marking the first known human case of this variant.

A 59-year-old resident of the State of Mexico succumbed to H5N2 bird flu on April 24, marking the first death from H5N2 bird flu. The individual had been hospitalised in Mexico City and exhibited symptoms including fever, shortness of breath, diarrhoea, and nausea.

Unknown Source of Exposure

The source of exposure to the H5N2 virus remains unknown, though the WHO has reported H5N2 cases in poultry in Mexico. This particular strain of bird flu, known as H5N2, is a subtype of the influenza A virus primarily affecting birds. It can occasionally infect mammals, including humans, when there is close contact with infected birds. The H5N2 virus can cause severe respiratory illness and other symptoms such as fever, diarrhoea, and nausea.

Background on H5N2 Bird Flu

H5N2 is one of many avian influenza viruses that have emerged in recent years. Avian influenza viruses are classified based on the combination of two proteins found on the virus surface: haemagglutinin (H) and neuraminidase (N). The H5N2 strain has been circulating among bird populations for several years, primarily affecting poultry. This strain is considered highly pathogenic to birds, leading to significant outbreaks in poultry farms, which can result in severe economic losses and necessitate culling to prevent further spread.

The virus spreads among birds through direct contact with secretions from infected birds, such as saliva, nasal secretions, and faeces. Contaminated surfaces and materials can also facilitate the spread of the virus. While human infections are rare, they can occur, typically in individuals with close contact with infected birds or contaminated environments.

In March 2024, Mexico reported H5N2 outbreaks in backyard poultry farms in Michoacan state, with additional cases detected in the State of Mexico. These outbreaks prompted increased surveillance and control measures to contain the virus and prevent further spread. Despite these efforts, the exact pathway through which the virus infected the 59-year-old individual remains unclear. Establishing a direct link between human cases and poultry infections often proves challenging due to the complex transmission dynamics of avian influenza viruses.

Monitoring and Surveillance

To mitigate the risk of further infections, Mexican health authorities have intensified monitoring efforts in regions with reported H5N2 outbreaks. Farms near the victim’s residence are under close observation, and a permanent surveillance system has been established to detect new cases in wildlife. Enhanced biosecurity measures are also being implemented to protect both poultry and human populations from the virus. The risk to the general population remains low, as confirmed by the WHO.

Underlying Health Conditions

The first death from H5N2 bird flu involved a 59-year-old with multiple underlying health conditions. The victim had chronic kidney disease, type 2 diabetes, and systemic arterial hypertension. According to health experts, these pre-existing conditions significantly increased the risk of severe complications from influenza. Even seasonal flu can be more dangerous for individuals with such health issues, making the impact of H5N2 potentially more severe.

The WHO noted that the deceased had no known history of direct exposure to poultry or other animals. This absence of known exposure raises concerns about unidentified transmission routes. Despite thorough investigations, health authorities have yet to determine how the individual contracted the virus. The lack of direct contact with infected birds complicates efforts to trace the infection’s origin and implement effective preventive measures.

Global Context of Avian Influenza

While this is the first confirmed human case of H5N2, other avian influenza strains have affected humans globally. For instance, the H5N1 strain has caused numerous infections and fatalities worldwide. H5 viruses, in general, have shown a propensity to infect mammals more frequently than other avian influenza viruses. This tendency highlights the need for vigilant monitoring and prompt response to any signs of avian influenza in both birds and humans.

Researchers and health authorities are continuously monitoring avian influenza viruses for mutations that might enhance their ability to spread among humans. Each human infection provides the virus an opportunity to adapt and potentially gain the capacity for human-to-human transmission. Enhanced surveillance, research, and international cooperation remain crucial in identifying and mitigating the risks associated with avian influenza viruses like H5N2.


Steenhuysen, J., & Barrera, A. (2024, June 6). WHO confirms first human case of avian influenza A(H5N2) in Mexico. Reuters.

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