H5N1 bird flu has spread to human from cow in 2nd probable case, CDC reports

A second human case of bird flu has been linked to the ongoing outbreak in cows on U.S. dairy farms, the Centers for Disease Control and Prevention (CDC) reported Wednesday (May 22). 

A subtype of avian iNFLuenza called H5N1 was initially discovered in U.S. cows in March and has since been detected among cattle in nine states. The commercial milk and meat supply is safe to consume, although raw milk samples from sick cows have been found to carry the virus, so unpasteurized milk might pose a risk of infection to humans. 

However, no human infections with H5N1 have yet been tied to consuming raw milk; the two human cases flagged so far affected dairy workers employed by farms with H5N1-infected cows. The first possible case of cow-to-human transmission, reported in April in Texas, involved an individual whose only symptom was eye redness. The second case, just identified in Michigan, also involved only eye-related symptoms. 

The person infected in Michigan tested negative for bird flu when a swab sample was taken from their nose, but an eye swab from the patient tested positive.

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"It's not known exactly how eye infections result from avian influenza exposures," the CDC report notes. They may arise from contamination of the eyes "with a splash of contaminated fluid," such as milk, or else touching the eyes with a hand contaminated with the virus. 

The CDC is now analyzing the genetic makeup of the virus that infected the Michigan patient and will release those data soon. In the meantime, the CDC still considers the risk of bird flu spread to the general public to be low.