Less than a week after California health workers confirmed the presence of the avian flu virus in store-bought raw milk, state agriculture officials visited the Raw Milk dairy in Mark McAfee “like never before” and began collecting samples from the farm’s two herds, creamery, bulk milk tanks and trucks, according to the owner.
The visit follows a recall of raw milk products and also comes amid a growing series of H5N1 bird flu outbreaks on dairy farms across the state. According to McAfee, Raw Farm has 1,800 head of cattle spread across two herds, one in Fresno and one outside Hanford. The company also has a creamery based in Fowler.
“I think they are in full attack mode,” he said, calling the search thorough. In addition to milk, Raw Farm produces cheese and kefir.
As California Department of Food and Agriculture officials collected samples and conducted tests at the dairy Wednesday, some health experts raised questions and concerns about recent positive test results.
Last week, Santa Clara County public health officials detected the avian flu virus in a sample of store-bought McAfee raw milk. Two days later, the California Department of Public Health confirmed this finding.
But when state agriculture officials tested cows at the McAfee Dairy Farm on Monday, they failed to detect the virus.
The fact that none of the animals were infected with the virus has both intrigued and worried public health experts. Typically, once the virus appears on a farm, it spreads and does not go away.
“The fact that all the additional tests are negative really bothers me,” John Korslund, a retired veterinary epidemiologist with the U.S. Department of Agriculture, said in an email.
CDFA officials could not be reached for comment Wednesday, but infectious disease experts told the Times that officials are likely reviewing testing procedures, as well as the actual origin of the sampled milk.
The initial sample of store-bought raw milk contained high levels of the virus and was found to have a polymerase chain reaction cycle threshold – or Ct – of around 25, according to testing records.
“A herd should not immediately be negative after a reading of 25 if it is truly milk from the same herd, IMO,” Korslund wrote in an email.
Richard Webby, director of the World Health Organization Collaborating Center for Studies on Influenza Ecology in Animals and Birds, and researcher in the Department of Infectious Diseases at St. Jude Children’s Research Hospital in Memphis, Tennessee, agrees.
“OK, it’s not a low positive … and certainly not at the borderline where some tests would be positive and some would be negative,” he said after reviewing test records.
Webby, Korslund and other experts say the test used only looks for the H5 part of the H5N1 virus and cannot determine whether the virus is inactive or alive. A second test – called a virus isolation test – must be done to confirm that the sample is H5N1 and is active.
State and federal health officials say the H5N1 avian flu virus poses a low risk to the public. However, they urged people not to drink raw, unpasteurized milk. No outbreaks associated with avian influenza present in contaminated raw milk have been reported among consumers.
The milk was bottled on November 9. Raw Farm LLC has recalled all products associated with the positive sample. McAfee estimates the recall affected approximately 2,000 gallons of half-gallon and quarter-gallon “cream” whole milk products.
Since the outbreak began, 461 herds have been infected in California, including herds in Fresno and Kings County, where McAfee’s herds are located.
Early in the H5N1 dairy outbreak, federal health officials tested samples of pasteurized milk and found the virus in 20% of samples collected from retail store shelves. However, when further testing was done – isolating the virus – they were able to show that it was an inactivated virus that had been denatured by heat.
So why would a raw milk sample test highly for the virus and a dairy herd not test positive?
Korslund acknowledged that testing and sampling can sometimes be compromised, but he was not inclined to doubt the testing in this case. He said the Ct value – and lack of subsequent positive tests – suggests a “product integrity issue rather than a herd infection”.
“What if, somewhere during the bottling process, preserved pasteurized milk was added to raw milk to meet insufficient supply demand? In such a scenario, we do not have a testing problem; rather, it is a product integrity issue that would normally be undetectable,” he said.
This is why virus isolation testing is essential, Korslund said. This would help determine whether the virus in the collected sample was alive or not.
A spokesperson for the state health department said testing on the sample had been completed. He did not say whether virus isolation had been completed, but noted that the positive result had been confirmed by state and now federal laboratories.
McAfee said he does not believe the virus is present in his herd. Tests that the state agriculture department does regularly — twice a week — on its bulk milk came back negative. Additionally, he noted, a test conducted Monday also showed no virus.
Additionally, he said, he monitors every cow on his farms with a high-tech device — made by Austrian company smaXtec — that sits in a cow’s udder and sends real-time information about the animal body temperature, milk acidity, etc.
He said there is no indication the virus is moving through his herd based on this data.
It also said all of its equipment – from its trucks to its bulk tanks and bottling plant – was closed to outside farms and milk; they are used only by Raw Farm, LLC.
He expressed concern that state officials are determined to “find something.”
