H5N1 avian influenza appears to be wreaking havoc on dairy farms in California, the largest milk-producing state in the U.S. The total number of infected cows in the herd has alarmingly doubled over the weekend, from 17 last Thursday to 34 as of Monday morning, according to state and federal officials.
The new tally puts California in second place among all affected states for the state with the most avian flu-infected herds. Only Colorado, which has implemented bulk milk tank surveillance, has more confirmed herds than California, with 64 confirmed herds. California ranks higher even though the state first reported three infected herds on Aug. 30, while infections on dairy farms were first identified on March 25 and are believed to have begun late last year.
To date, 232 flocks in 14 states have been infected with avian influenza.
California officials said in a statement last week that the herds that tested positive “were targeted for testing due to their increased risk due to their recent association with the first affected facility.” They said the positive cases were “not unexpected” and fit with the state’s plan to detect the outbreak as early as possible. “Early detection provides an opportunity to work with farms to quickly strengthen biosecurity, cattle care and employee protections.”
When the state’s first infected flock was announced, California Department of Food and Agriculture Commissioner Karen Ross touted the state’s preparedness and readiness. “Our state’s extensive experience with (highly pathogenic avian influenza) in poultry means we are well prepared and have the expertise to handle this event,” she said. She also assured dairy farmers that the outbreak is being addressed with “the utmost urgency.”
Problematic transmission
The news comes as public health experts express concern over a mysterious case of H5 avian influenza reported in a Missouri individual with underlying health conditions but no history of exposure to animals. This case marks the 14th human infection caused by dairy cattle infection this year. All 13 previous cases were farm workers with a history of exposure to infected animals, including nine poultry workers and four dairy workers. However, Missouri has not reported any H5N1 infections in dairy herds, and no recent infections have been reported in poultry facilities.
The Missouri patient has recovered, but health officials are puzzled as to how he or she was infected. At a press conference earlier this month, a Centers for Disease Control and Prevention official suggested the infection may have been a “one-off.” However, the CDC reports that another person who lived in the same household as the Missouri patient also became ill, suggesting a shared exposure to the virus. Contacts of the family were not tested for influenza and have since recovered. The CDC is now conducting serological tests to see if the family has developed antibodies to avian influenza, suggesting prior infection.
The CDC also reports that a health care worker who had been in contact with the patient became ill but tested negative for influenza. On Friday, the CDC reported that a second health care worker developed a mild respiratory illness after contact with the Missouri patient, but was not tested for influenza and recovered before the investigation began. The CDC will also offer serology testing to this health care worker.
While there is no evidence of human-to-human transmission yet, health experts are concerned that insufficient testing of contacts of infected people, animals, and farm workers is allowing the infection to continue unseen. As this insidious influenza virus spreads across the country and infects new mammalian species, it creates new opportunities for it to adapt to humans and cause more severe disease. Influenza experts have long worried that this virus could cause a pandemic.
