University of Nebraska Medical Center

Bird flu discovered in U.S. dairy cows is ‘disturbing’

Science Scientist who tracks infections on cattle farms discusses implications of recently announced virus detections.

The bird flu virus that has wreaked havoc around the world appears to have surfaced in U.S. dairy cows, the first time this viral subtype has been documented in any cattle. Three U.S. states—Texas, Kansas, and New Mexico—on 25 March reported cows sickened with what scientists are presuming is the same H5N1 strain of influenza that has killed hundreds of millions of poultry and wild birds.

The cattle infections are spoiling milk and causing limited disease in mostly older animals. Dead birds have also been found on some of the farms, which may explain the source of the virus. Public health officials have stressed that the risk to humans from the virus remains low.

The so-called highly pathogenic avian influenza (HPAI) virus spreading in birds has already been documented to infect dozens of other mammalian species, but rarely spreads between them. Earlier this month, HPAI was found in a goat in Minnesota, the first case in U.S. livestock. Gregory Gray, an epidemiologist at the University of Texas Medical Branch, calls the new detections in cows across multiple states a “worrisome” development because it may signal this bird flu strain is spreading directly between cattle, instead of via birds, and has mutated in ways that could allow it to better infect people. But preliminary studies on the affected cows show no signs that the virus has changed, the National Veterinary Services Laboratories said in a statement yesterday.

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