Avian flu infects dairy cows in more than a dozen U.S. states – microbiologist explains how the virus spreads

The current H5N1 strain of avian influenza has led to the culling of millions of poultry birds, More than 12 farmworkers fell ill in 2024, Recently in Colorado.

The Conversation US asked Immunologists and Microbiologists Jenna Guthmiller A lecturer from the University of Colorado Anschutz Medical Campus explained the historical roots of H5N1, how it is transmitted, and how to avoid contact.

What is H5N1?

H5N1 Influenza A virusOther well-known subtypes of influenza A viruses include: H1N1 and H3N2which causes seasonal epidemics in humans.

Unlike H1N1 and H3N2, H5N1 primarily infects wild birds, with waterfowl such as ducks and geese being the natural hosts of the H5N1 virus. Most H5N1 viruses Highly pathogenic avian influenzaThis means that spillover effects on other bird populations could lead to high mortality rates. Including poultry.

The H5N1 virus was first identified in 1959. Scottish domestic chickensIn 1996, waterfowl were identified as the natural host of H5N1.

Since its discovery, the H5N1 virus has caused four major epidemics: in 1997, 2003-2005, 2015, and from 2021 to the present. Outbreaks in 1997 and 2003-2005 led to Huge ripple effects To humans.

Nearly 900 cases of H5N1 infection in humans have been documented since 2003. Of these infections, More than half died.

Where did H5N1 originate?

The current H5N1 epidemic Starting in late 2021 and, The virus that caused the 2015 pandemic.

Since 2021, H5N1 has spread to six continents via migratory birds. Impact on domestic poultry led to The extermination of millions of pet birds

Researchers have documented that the current H5N1 strain is infecting many mammal species, primarily affecting aquatic mammals. Such as seals and other scavenging mammals.Sporadic spills have been recorded in domestic mammals such as minks, goats and alpacas.

In March 2024, the United States Department of Agriculture reported an outbreak of H5N1. Lactation period of dairy cowsAs of August 27, there were 192 herds in 13 states. Confirmed positive for H5N1.

H5N1 viruses associated with dairy cattle have subsequently reinfected wild birds, and recent outbreaks in poultry resemble those in dairy cattle. 13 confirmed cases of H5N1 infection It has also occurred in humans, and all cases are directly related Dairy and poultry culling.

Why did bird flu spread?

It's unclear why H5N1 has become such a widespread problem — like other influenza viruses, it can mutate rapidly and infect new hosts — but H5N1 has some characteristics that may allow it to expand its host range.

First, the H5N1 virus Hemagglutinin This allows H5N1 to infect new hosts.

Second, my research group identified a mutation in the H5N1 virus that is responsible for the spread of infection in dairy cows. Allows hemagglutinin to bind to receptors more efficiently.

Finally, H5N1 viruses have mutated genes related to replication and immune evasion, Increase mammalian infections.

The combination of these factors may facilitate H5N1 transmission and increase the spillover of H5N1 into mammals.

How does this strain get transmitted to dairy cows?

The H5N1 virus primarily causes infection in the mammary gland of cows, rather than in the respiratory system, which is the primary site of infection for other influenza viruses in mammals. Mammary tissue contains receptors for H5N1This can make this tissue more susceptible to infection.

Because infection is largely confined to the mammary gland, researchers believe H5N1 is transmitted to cows by contaminated milking equipment, specifically milking devices attached to the cow's udders. Transmission between farms is also possible. Movement of infected cattle and Sharing of facilities and personnel across the dairy farm.

In an effort to curb the spread of the disease, the USDA implemented testing requirements in April 2024. When cattle are transported across state linesAdditionally, in Colorado, the state with the most positive herds, Mandating weekly testing on farms To Identifying infected herds.

What are the risks to humans and other animals?

H5N1 does not pose a risk to the general public as it is not known to be transmitted from person to person. All known cases have been due to direct contact with infected animals, so people with occupational contact with H5N1-infected cattle or poultry remain at greatest risk of infection.

People who are occupationally exposed should be on the lookout for flu-like symptoms of H5N1, such as stuffy nose, sore throat and fatigue. conjunctivitiscommonly known as pink eye. For more information, see the Centers for Disease Control and Prevention's Avian Influenza Webpage.

Livestock and wildlife living near dairy farms are at high risk of infection, particularly as there have been reports of deaths of barn cats fed raw milk on dairy farms with infected cows. These animals tested positive for H5N1..

In addition, the H5N1 virus can spread to other livestock kept in close proximity to infected dairy cows. Recorded.

What is the best way to keep farmworkers safe?

Using personal protective equipment such as goggles and gloves is the best way to prevent H5N1 from spreading to humans and from humans to animals. People who work around poultry or dairy cattle should also take care to: Biosecurity measuresFor example, not wearing the same clothes or boots when moving from farm to farm.

Is it a problem to drink dairy milk?

As long as you are Consumption of pasteurized dairy productsThere is no concern about human infection. Sterilization It is highly effective in killing the H5N1 virus that may have contaminated milk.

Due to the discovery of the H5N1 virus, raw and unpasteurized milk should be avoided. Very high concentration in raw milk.