The H5N1 bird flu appears to be sweeping through dairy farms in California, the nation’s largest milk producer. Over the weekend, the total number of confirmed infected cow herds doubled in a stunning fashion, from 17 last Thursday to 34 Monday morning, state and federal officials said.
The new count puts California second among all affected states with the most flocks infected with avian influenza. Only Colorado, which has implemented bulk milk tank surveillance, has more, with 64 confirmed flocks. California’s high ranking is despite the fact that it only reported its first three infected flocks on August 30, while the dairy outbreak was first confirmed on March 25 and was thought to have begun late last year.
To date, 232 flocks in 14 states have been infected with bird flu.
In an announcement last week, California officials said the group of herds that tested positive were “targeted for testing due to increased risks from their recent connections to the first affected locations.” They called the positive results “not unexpected” and said they fit with the state’s plans to find infections as early as possible. “Early detection provides an opportunity to work with farms to quickly implement enhanced biosecurity, cow care, and worker protections.”
When the state's first infected herds were announced, California Secretary of Food and Agriculture Karen Ross praised the state's preparations and readiness. “Our extensive experience with [highly pathogenic avian influenza] in poultry has given us ample preparation and expertise to address this incident,” Ross said. She further assured dairy farmers that they are approaching the outbreak with “the utmost urgency.”
Problematic transmission
The news comes as public health experts are concerned about a mysterious case of H5 bird flu in a person in Missouri who had underlying medical conditions but no known animal contact. The case is the 14th human infection during this year’s dairy cow outbreak. All 13 previous infections were in farm workers known to have had contact with infected animals: nine in poultry workers and four in dairy workers. But Missouri has not reported H5N1 in dairy herds and has not had any recent outbreaks in poultry farms.
Although the Missouri case has recovered, health officials are still puzzled by how that person became infected. In a press conference earlier this month, a Centers for Disease Control and Prevention official suggested the case could be a “one-off.” But the CDC said another person in the Missouri case’s household became sick at the same time, suggesting a possible shared exposure to the virus. That household contact was not tested for the flu and has since recovered. The CDC is now conducting serology tests to see if the household member has developed antibodies to bird flu, indicating a previous infection.
The CDC also reported that a health care provider who interacted with the patient became ill but tested negative for influenza. On Friday, the CDC reported that a second health care provider became ill with a mild respiratory illness after interacting with the Missouri case but was not tested for influenza and recovered before the investigation began. The CDC will also offer serology testing for that health care provider.
While there is no evidence of human-to-human transmission, health experts fear that there is insufficient testing—of case contacts, animals or farm workers—and that transmission is going undetected. As the wily influenza virus spreads across the country to new mammal species, it is getting new opportunities to adapt to humans and cause more severe disease. Influenza experts have long feared that the virus has pandemic potential.
