Countries worldwide need to enhance surveillance for detecting changes in influenza viruses, given the recent confirmation of the first human case of A(H5N2), or bird flu, infection globally and the first A(H5) virus infection in a person in Mexico.

The World Health Organization (WHO), in a release on June 5, stated that the Mexico case was caused by a combination of underlying conditions. Therefore, health authorities in the country are currently conducting an investigation to determine the source of exposure.

WHO said Mexico’s International Health Regulations (IHR) National Focal Point (NFP) reported it to the Pan American Health Organization (PAHO), a specialized international health institution for the Americas, on May 23. PAHO then confirmed the fatal human infection with avian influenza.

The case was detected on April 17 in a 59-year-old resident of the State of Mexico who was admitted to a hospital in Mexico City. The person had no prior history of exposure to poultry or other animals. Further investigation stated that the deceased had been confined to bed for three weeks prior to the onset of acute symptoms.

The symptoms recorded included fever, difficulty breathing, diarrhea, nausea, and general malaise. The individual sought medical attention on April 24 but died on the same day.

WHO said the respiratory sample collected and tested at the National Institute of Respiratory Diseases Ismael Cosio Villegas on April 24 initially indicated a non-subtypeable influenza A virus. Subsequent sequencing at CIENI confirmed it as influenza A(H5N2) on May 8. Further analysis at InDRE on May 20 confirmed influenza A and subtype A(H5N2) on May 22.

No further instances were documented during the investigation. Out of the 17 people who had contact with the hospital, only one person experienced moderate symptoms. However, further tests confirmed that they did not have influenza or SARS-CoV-2. A total of twelve more individuals in close proximity to the patient’s home were discovered, and samples taken from them yielded negative results for both viruses.

“Whenever avian influenza viruses are circulating in poultry, there is a risk for infection and small clusters of human cases due to exposure to infected poultry or contaminated environments. Therefore, sporadic human cases are not unexpected. Human cases of infection with other H5 subtypes including A(H5N1), A(H5N6) and A(H5N8) viruses have been reported previously,” the WHO said.

Avian influenza A(H5N2) outbreaks were documented in March 2024 in chicken farms located in Michoacán and Texcoco, State of Mexico. Subsequently, in April, more outbreaks were detected in Temascalapa. The connection between these outbreaks and the human case is yet uncertain.

Animal influenza viruses normally circulate in animals but can also infect humans. Infections in humans have primarily been acquired through direct contact with infected animals or contaminated environments, the international public health organization explained.

Depending on the original host, influenza A viruses can be classified as avian influenza, swine influenza, or other types of animal influenza viruses.

Avian influenza viruses have the potential to cause a range of respiratory tract illnesses in humans, varying in severity from mild to severe, and in certain instances, they can result in death. WHO claimed there have been reports of symptoms such as conjunctivitis, gastrointestinal problems, encephalitis, and encephalopathy.

As influenza viruses keep changing, WHO keeps reminding health leaders to keep an eye on them worldwide.

“When there has been human exposure to a known outbreak of an influenza A virus in domestic poultry, wild birds or other animals or when there has been an identified human case of infection with such a virus, enhanced surveillance in potentially exposed human populations becomes necessary,” it said.

“Enhanced surveillance should consider the healthcare-seeking behaviour of the population. It could include a range of active and passive healthcare and/or community-based approaches, including enhanced surveillance in local ARI/ILI/ SARI systems, active screening in hospitals and of groups that may be at higher occupational risk of exposure, and inclusion of other sources such as traditional healers, private practitioners and private diagnostic laboratories,” it added.

WHO reminded that when investigating the spread of a new virus, it’s important to quickly identify any unusual occurrences that might indicate the virus is passing between people.

Samples taken from individuals suspected of being infected should be tested, and if necessary, sent to a WHO Collaboration Centre. These centers have the expertise and resources needed to analyze the samples in more detail and better understand the virus.

Travelers to countries, where animal influenza outbreaks are happening, are also advised to take precautions. They should avoid places like farms, live animal markets, and areas where animals are being slaughtered.

It’s also important to steer clear of surfaces that might have animal waste on them. Travelers should wash their hands frequently with soap and water and follow good food safety practices.

“Should infected individuals from affected areas travel internationally, their infection may be detected in another country during travel or after arrival. If this occurs, further community-level spread is considered unlikely as this virus has not acquired the ability to transmit easily among humans,” stated the WHO.