Bird flu is on the move – these are the different strains worldwide – National

Avian influenza, or bird flu, has public health officials on edge after an unprecedented spread among dairy cows in the United States this year. Four dairy farmers 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 deadly outbreaks in commercial poultry and sporadic infections in other species from alpacas to domestic cats. Until this year, it had never infected cows.

Several strains of bird flu have been found in humans in Australia and Mexico, while several H5 subtypes also occur in both animals and humans around the world, in countries such as China and Cambodia.

Click to play video: 'Infectious disease doctors issue guidance for Canada on bird flu'

Infectious disease doctors issue guidelines for bird flu in Canada

Most human cases involve exposure to poultry, live poultry markets or dairy cattle before infection, but scientists worry the virus could mutate in ways that make it easier to spread from person to person, potentially causing a pandemic. The World Health Organization says the risk to humans is low at this time.

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Below are the cases of different types of 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 there are now dairy herds in 12 states. The U.S. Department of Agriculture said tests so far indicate the virus found in cows is the same H5N1 virus that affects wild birds and commercial poultry herds. The four dairy farmers who 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 clade, genotype B3.13, a genotype that has so far only been found in North America, the European Food Safety Authority said in a scientific report.

Click to play video: 'Health Matters: Fourth US Dairy Worker Gets Bird Flu'

Health Affairs: Fourth US Dairy Worker Gets Bird Flu

A Mexican resident has died in the first known cases of H5N2 bird flu in humans, the WHO reported June 5. Mexican authorities said chronic illness, rather than bird flu, was the cause of death. The person was not known to have been infected with animals.

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The WHO reported on June 7 that a child with H5N1 bird flu, reported from Australia, had traveled to Kolkata, India. Genetic sequencing showed the virus was a subtype of H5N1 and part of a strain circulating in Southeast Asia and has been detected in previous human infections and in poultry.

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Australia is dealing with three separate outbreaks of different strains of the virus on poultry farms – H7N3, H7N8 and H7N9 – which authorities say likely entered the farms via wild birds.

Click to play video: 'Australia, US report second bird flu cases in humans'

Australia, US report second bird flu cases in humans

The WHO reported a case of human infection with bird flu caused by the H9N2 subtype in a four-year-old child in the eastern Indian state of West Bengal on June 11. It was the second human infection with H9N2 bird flu from India after a case in 2019, the agency said. While the H9N2 virus typically causes mild illness, the United Nations agency said more sporadic human cases are possible as it is one of the most common bird flu viruses circulating in poultry in several regions.

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Vietnam reported that a 21-year-old student died in March from H5N1 bird flu. He had no underlying medical conditions, but had been exposed to wild birds through hunting a few weeks before his symptoms began. There were no reported contacts with dead or sick poultry at the time.

According to EFSA, Vietnam also reported an outbreak of H9N2 in a 37-year-old man.

The Southeast Asian country and neighboring Vietnam reported five human cases of H5N1 as of June 20.

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China has discovered human cases caused by the H5N6, H9N2 and H10N3 strains this year, with two fatal H5N6 cases in Fujian province. Both cases had exposure to backyard poultry before the onset of symptoms, EFSA said.

The case of H10N3 bird flu was the third case ever reported worldwide.

Click to play video: 'China reports bird flu outbreak at farm in Hunan province'

China reports bird flu outbreak at farm in Hunan province

Germany reported a rare outbreak of the highly pathogenic H7N5 bird flu on a farm in the western part of the country, near the border with the Netherlands, the World Organisation for Animal Health reported on July 4. It was the first outbreak of H7N5 anywhere in WOAH’s public records.

Katie Dangerfield

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