The “primary vector” for transmitting the H5N1 bird flu virus from dairy cow to dairy cow seems to be milk from an infected animal, said the USDA’s chief veterinary officer on Wednesday. Dr. Rosemary Sifford also said the USDA was considering whether to offer compensation to dairy farmers for cooperating in the investigation of the disease and for adopting stronger biosecurity safeguards.
Bird flu was discovered in cattle for the first time in late March following reports of a mysterious illness in milk cows in the Texas Panhandle. During a teleconference with FDA and CDC officials, Sifford said the H5N1 virus had jumped to cattle from wild birds in a “spillover event” involving “a number of herds in that region.”
“We believe milk is the primary vector” for spreading the virus, she said. Milk from infected cows has a high viral load. “We believe the primary mode of transmission [is] through contact with the milk.”
The FDA’s Donald Prater said a second round of high-precision tests, involving 201 retail samples of milk and dairy products, showed that “pasteurization is effective in inactivating” the bird flu virus. The samples included sour cream and cottage cheese. The FDA also tested infant and toddler formula and found those products to be free of the virus and viral fragments.
A Texas dairy worker was treated for mild symptoms — conjunctivitis — of bird flu in early April, the first known instance of a human being infected with the virus. The CDC said there have been no signs of an increase in flu or bird flu-like illness. “The current risk to human health is low,” said Dr. Demetre Daskalakis of the CDC.
Disease experts have pointed to milking parlors as a possible place for cow-to-cow infection. The same milking equipment is used on multiple animals, and a few contaminated drops on the equipment might be enough to spread the virus to the next cow, they said. The USDA has identified cow-to-cow, cow-to-poultry and herd-to-herd movement of the virus.
Under a federal order that went into effect on Monday, dairy farmers are required to test lactating cows for the H5N1 virus before shipping them across state lines. The USDA will pay the cost of the tests. Sifford mentioned the possibility of compensation after reporters asked if farmers have been reluctant to have their stock tested.