Bird flu is on the move — here are the different strains around the world

Bird flu, has public health officials on alert after an unprecedented spread in dairy cows in the U.S. this year. Four dairy workers have also tested positive in the country.

Avian influenza, or bird flu, has public health officials on alert after an unprecedented spread in dairy cows in the United States this year. Four dairy workers have also tested positive in the country.

A particularly severe variant of the H5N1 strain has been spreading around the world in animals since 2020, causing lethal outbreaks in commercial poultry and sporadic infections in other species from alpacas to house cats. Until this year, it had never infected cows.

Different bird flu strains have been found in Australia and Mexico in humans, while different H5 subtypes are also present around the world in both animals and humans, in countries including China and Cambodia.

Most of the human cases reported exposure to poultry, live poultry markets, or dairy cattle prior to infection, but scientists are worried the virus could mutate in ways that make it more easily spread from person-to-person, which could spark a pandemic. The World Health Organization says the risk to people is low at this point.

Below are occurrences of varying types of the bird flu virus that have been found in humans this year.

The first known cases of infected dairy cattle occurred in Texas in March, and is now in dairy herds in 12 states. The U.S. Agriculture Department said tests so far indicate that the virus detected in cows is the same H5N1 virus affecting wild birds and commercial poultry flocks. The four dairy workers who have tested positive for the virus this year had mild symptoms such as conjunctivitis, or pink eye.

The H5N1 virus in the United States belongs to the clade 2.3.4.4b, genotype B3.13, a genotype detected only in North America so far, the European Food Safety Agency said in a scientific report.

A resident of Mexico died with the first known cases of H5N2 avian influenza in humans, the WHO said on June 5. Mexico’s government said chronic illness, rather than bird flu, was the cause of death. The person had no known exposure to animals.