Dear Doctors: I would like to know more about bird flu and how it gets transmitted. Have any people in the United States gotten sick with it? I heard on the news that it has moved into cows. Does that mean you can get it from drinking milk?
Dear Reader: Bird flu, also referred to as avian influenza, is a type A influenza virus. It is also known as H5N1, a designation that refers to the specific combination of two groups of proteins that identify various subtypes of the virus.
Bird flu is widespread in wild birds, and in that population, which has developed immunity, it usually results in few symptoms. However, the same virus, when transmitted to domesticated poultry, is lethal. In the U.S., bird flu has caused outbreaks in poultry in 48 states. It has also infected other animals, including dairy cows.
H5N1 infection in humans has been extremely rare. When the virus does move from an animal to a human, the resulting illness can range from causing no symptoms or very mild symptoms to severe disease that can be fatal. Transmission of the virus is via close contact with an infected animal, or with their saliva, mucus or feces. There has been no known person-to-person transmission of the H5N1 virus.
At this time, there have been two confirmed cases in the U.S. of transmission of the H5N1 virus from an animal to a human. One occurred in a poultry worker in Colorado in 2022. His symptoms were limited to fatigue. The most recent case affected a farm worker in Texas, whose primary symptom was conjunctivitis, also known as pink eye. Both individuals were successfully treated with antiviral medications. It’s the more recent infection, which occurred on a dairy farm earlier this spring, that brings us to your question about bird flu and cows.
Both the U.S. Centers for Disease Control and Prevention and the Food and Drug Administration are actively monitoring the presence of avian influenza in cows. The latest information confirms outbreaks in 34 dairy herds in nine states. Testing for H5N1 virus in milk samples has found the presence of viral particles. However, the process of pasteurization, in which milk is heated to high temperatures to kill other types of pathogens, is effective at killing the influenza virus, as well. As a result, pasteurized milk and milk products do not present a danger. The FDA has also announced that it is collecting and testing samples of ground beef offered for sale in states with outbreaks of bird flu in dairy cows. Lactating dairy cows are also now required to test negative for H5N1 virus before being allowed to cross state lines.
For most people, the overall risk of contracting bird flu is extremely low. The CDC and the World Health Organization say that those at greatest risk are farm workers and others who have regular and prolonged contact with poultry and dairy cattle. The Department of Agriculture has also begun to use a so-called virus surrogate to conduct tests on cooking times to determine the temperature to which meat must be heated in order to kill the H5N1 virus. The agency says it plans to release that data as it becomes available.
(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)
