In the nearly seven months since bird flu was identified in dairy cattle in Texas, the virus has infected 20 people — all but one of them livestock workers — and been found in 300 herds in 14 states from North Carolina to California. “The epidemiology of the situation continues to suggest sporadic instances of animal-to-human spread,” rather than the virus gaining power to spread among people, said the Centers for Disease Control.
California is the hot spot for bird flu; six infections were confirmed among dairy farmworkers in the seven days ending on last Thursday, all in the Central Valley. “Proactive testing” has found five possible human cases, also in the Central Valley, said the California Department of Public Health on Monday. The 11 individuals (the six confirmed infections and five possible bird flu cases), “had direct contact with infected dairy cattle at nine different farms,” said the state health department.
The “jump” of the H5N1 avian flu virus to cattle from birds increased the opportunity for the virus to develop communicability among people, a worrisome possibility. To date, the CDC says genomic sequencing has not found changes associated with increased infectivity or transmissibility among humans or reduced susceptibility to antiviral medications. The risk to the general population remained low, it said.
All of the people with confirmed and possible cases of bird flu in California were treated for mild cases of bird flu, with symptoms that included conjunctivitis. No one was hospitalized.
Besides the six confirmed cases in California, 10 poultry and cattle workers in Colorado have contracted bird flu this year, along with two in Michigan. One illness has been reported in Missouri and Texas.
California was home to 100 of the 300 infected dairy herds in the nation, said a USDA database. Colorado was second with 64 herds and Idaho was third with 34 herds. California’s first outbreak, in three herds, was on Aug. 30. Some states have gone weeks without an outbreak. For example, Colorado’s more recent confirmation was Aug. 13.
As part of its farmworker surveillance program, the CDC said it was developing a pilot program to offer free tests of symptomatic people in California and one other state. “The program aims to increase testing for seasonal flu and triage for H5 testing if needed, raise awareness about the symptoms and risk factors for infection with H5N1 bird flu among higher-risk populations, and determine whether certain rapid point-of-care [POC] tests identify influenza A-positive specimens when farm or dairy workers are infected with H5N1 bird flu.” said the CDC in a weekly update.
More than 5,100 people have been monitored as a result of exposure to infected or potentially infected livestock and at least 250 have been tested for bird flu after developing flu-like symptoms.
Highly pathogenic avian influenza has killed nearly 101 million birds in domestic flocks since the H5N1 virus, which has spread worldwide, appeared in the United States in February 2022.
Bird flu is much milder in cattle, most frequently causing fever, a loss of appetite and a sharp reduction in milk output. Most cows recover within a few weeks and the mortality rate has been 1 or 2 percent. But there were reports of higher mortality among California herds.
California veterinarian Crystal Heath, an advocate of stronger biosecurity standards, found piles of dead dairy cows at two farms near Tulare, in the Central Valley, reported Newsweek. A dairy industry spokesman said rendering plants were slow in collecting the carcasses because of bird flu outbreaks.