A multistate outbreak of bird flu in dairy cows that was first reported in March is continuing to grow and has now infected more than 100 herds across America.
As of June 13, the highly pathogenic avian influenza A(H5N1) virus has been detected in 101 herds in 12 states, according to latest figures from the U.S. Department of Agriculture, the Food and Drug Administration, and the Centers for Disease Control and Prevention.
Affected states include Colorado, Idaho, Iowa, Kansas, Michigan, Minnesota, New Mexico, North Carolina, Ohio, South Dakota, Texas and Wyoming.
This is the first time that the bird flu virus had been found in cows. The outbreak was first reported on March 25, when the USDA confirmed the A(H5N1) virus was detected in dairy cows in Texas and Kansas. It was also later confirmed in cows in Idaho, Michigan and New Mexico.
Unpasteurized milk from sick cattle collected from two dairy farms in Kansas and one in Texas, as well as a throat swab from a cow in another dairy in Texas, tested positive for the same strain that is widespread among birds globally, according to the CDC.
Mammals can be infected with bird flu viruses when they eat infected birds, poultry or other animals, or if they are exposed to environments contaminated with virus. Spread from mammal to mammal is thought to be rare, but possible.
There are no concerns with the safety of the commercial milk supply at this time because products are pasteurized before entering the market, according to FDA and USDA. Dairies are required to send only milk from healthy animals into processing, while milk from impacted animals is destroyed so that it does not enter the food supply.
On April 1, the CDC reported a dairy worker in Texas tested positive for the virus, saying the person was likely infected by sick cattle. This is thought to be the first instance of mammal to human spread of the A(H5N1) virus. Since then, the virus has been detected in two dairy farm workers in Michigan who had exposure to infected cows. The CDC said none of the three cases are associated with the others.
"Given the extent of the spread of this virus in dairy cows, additional human cases in people with higher risk exposures would not be surprising," the CDC said. "Risk depends on exposure, and in this case, the relevant exposure is to infected animals. The risk to members of the general public who do not have exposure to infected animals remains low."
People with close or prolonged, unprotected exposures to infected birds or other animals (including livestock), or to environments contaminated by infected birds or other infected animals, are at greater risk of infection and should take precautions. There is no indication of person-to-person spread of A(H5N1) viruses at this time.
Human illnesses with bird flu viruses have ranged from mild (eye infection, upper respiratory symptoms) to severe illness (such as pneumonia) that have resulted in death in other countries, according to the CDC.
The symptoms of infection in humans include fever, cough, sore throat and muscle aches. Other early symptoms may include abdominal pain, chest pain and diarrhea. The infection may progress quickly to severe respiratory illness (difficulty breathing or shortness of breath, pneumonia) and neurologic changes (altered mental status, seizures).
On April 24, the USDA announced a federal order that requires mandatory testing prior to the interstate movement of lactating dairy cattle and mandatory reporting of positive influenza A test results in livestock. Officials say this testing is critical to increasing the information available to the USDA and to limiting potential virus spread through livestock movement.
Federal authorities say they are addressing the situation with urgency and through a whole-of-government approach to mitigate risks to workers and the general public, to ensure the safety of America's food supply and to mitigate risk to livestock, owners and producers.
The USDA is working closely with federal partners at the FDA, which has the primary responsibility for the safety of milk and dairy products, by assisting with conducting pasteurization testing at USDA labs. The USDA is also working closely with federal partners at CDC by encouraging producer and industry cooperation with public health officials to get vital information necessary to assess the level of risk to human health.