Rapid spread of H5N1 bird flu through California dairy herds suggests unknown paths of transmission Experts are skeptical that USDA’s theory of viral spread is telling the whole story

https://www.statnews.com/2024/12/20/california-h5n1-bird-flu-emergency-declaration-avian-flu-spread-dairy-cattle/?utm_campaign=morning_rounds&utm_medium=email&_hsenc=p2ANqtz-9VApBhtqX_hplf5pPTiCBRdbkXT3OrlWCUl6Ld2Blw_M-UGwf0saZioiFColk_zrPPl7R6NkBFjWJYvK-MDvdHzwMrTA&_hsmi=339774288&utm_content=339774288&utm_source=hs_email California scrambling to understand scale of bird flu spread California animal health authorities are now testing milk from all 984 of the state’s dairies on a weekly basis, stepping up its efforts to find new H5N1 infections in cattle. In a call with reporters Friday, California state veterinarian Annette Jones said that the new strategy was implemented two weeks ago, after the virus was found on a farm in Southern California. The majority of the state’s 659 infected herds have been concentrated in the Central Valley. The rapid spread of H5N1 in California has nfectious disease experts questioning how well authorities understand how the virus is moving between farms. Jones said California has dozens of research projects underway to study this question. But she also noted that cows may be asymptomatic for a number of weeks—which could have contributed to infected animals unwittingly being moved to new farms during the early stages of California’s outbreak. The unchecked spread is also leading to new human cases. The California Department of Public Health reported Friday two more H5N1 infections, both in dairy workers, raising the state’s total to 36. State epidemiologist Erica Pan told reporters that health officials have monitored about 5,000 people and tested 130 who had potential symptoms. She also added that officials have been investigating numerous detections of H5N1 at wastewater sites throughout the state, and that at the present time, there is still no evidence of human-to-human transmission. “Almost all of our wastewater testing sites are detecting H5 now,” she said. However, officials suspect that much of what they’re picking up is not live virus, but inactivated bits of viral RNA in pasteurized milk. “We think a lot of our wastewater detections are actually just from residential or other commercial milk dumping,” Pan said. — Megan Molteni