The World Health Organisation (WHO) has confirmed the first confirmed human case of the H5N2 type of bird flu in a 59-year-old man in Mexico who died in April.
WHO said in a statement on Wednesday that the Mexican health authorities reported the confirmed case to the UN health body on May 23 after conducting laboratory tests.
WHO said the man died after developing a fever, shortness of breath, diarrhea, nausea and general discomfort, the global health body said the cause of his death was only revealed in May after the result of laboratory test conducted was released.
It stated that 59-year-old man, whose identity was not given, had been hospitalised in Mexico City.
The WHO said Wednesday it wasn’t clear how the person became infected. “Although the source of exposure to the virus in this case is currently unknown, A(H5N2) viruses have been reported in poultry in Mexico,” it said in a statement.
It added that the Mexico’s Ministry of Health said the man had underlying health conditions, including kidney disease, diabetes, and high blood pressure.
However, the UN agency said the current risk of the bird flu virus to the general population in Mexico is low.
Mexico’s health ministry also said in a statement on Wednesday that there had so far been no evidence of person-to-person transmission of bird flu in the case of the man who died, and that he had several prior health conditions. All people who had contact with him have tested negative, it said.
In March, Mexico’s government reported an outbreak of A(H5N2) in an isolated family unit in the country’s western Michoacan state, but said at the time it did not represent a risk to distant commercial farms, nor to human health.
After the April death, Mexican authorities confirmed the presence of the virus and reported the case to the WHO, the agency said.
There had been three poultry outbreaks of H5N2 in nearby parts of Mexico in March, but authorities haven’t been able to find a connection.
Scientists said the case in Mexico is unrelated to the outbreak of a different strain of bird flu – H5N1 – in the United States that has so far infected three dairy farm workers.
Other bird flu varieties have killed people across the world in previous years, including 18 people in China during an outbreak of H5N6 in 2021, according to a timeline of bird flu outbreaks from the US Centers for Disease Control and Prevention.
What is H5N2?
H5N2 is just one of several kinds of avian influenza viruses. Does it actually pose a significant health risk to humans?
An exposure to H5 virus in Mexico isn’t surprising, said Dr. Troy Sutton, an assistant professor of veterinary and biomedical sciences at Penn State. H5 viruses have been circulating among poultry and wild birds in Mexico since the mid-1990s. However, unlike other avian influenza strains that have caused outbreaks in humans — such H1 and H3 viruses — H5 viruses rarely infect humans.
The viruses are classified based on two types of protein 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 primarily infects wild birds. There are a total of nine known subtypes of H5 viruses, according to the Centers for Disease Control and Prevention.
H5N1, which was detected in dairy cows in the U.S. in March, also belongs to this family. It is commonly associated with highly contagious strains of H5 viruses called the “Goose Guangdong lineage” that have caused numerous outbreaks in poultry over the last 20 years and sporadic infections in humans, said Sutton.
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 sort of story around the disease they cause,” Sutton said of the H5N2 and H5N1 viruses.
Should people be concerned?
The patient in Mexico had been bedridden for several weeks prior to developing symptoms.
According to 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 that it’s important to note that the man had multiple underlying medication conditions, which likely exacerbated his infection.
“The person may have already been quite sick,” Sutton said. “That changes the calculation a little bit 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 monitored at the hospital where the patient died, one reported a runny nose.
However, experts still don’t know how the man became infected with the virus, as he wasn’t exposed to poultry or to other animals. If he was infected by another human that suggests that there could be additional unidentified cases.
“It is concerning that a new virus subtype 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 likely picked it up from the same place.”
Data shows that the H5N2 virus that infected the man is a low pathogenic virus, meaning it is unlikely to cause severe illness, said Osterholm.
“There’s high path and low path, and the high path has certain genetic changes. It makes it much more likely to cause serious illness,” Osterholm said. “And the readily transmitted low path oftentimes can infect any number of animal species with little or no symptoms.”
With The Guardian (of London) and NBC News reports
