Learn the Facts About Avian Flu (H5N1)

While flu viruses sometimes jump from species to species, there are some new developments with this H5N1 virus:

•  Before this year, H5N1 bird flu viruses had never infected cows

•  The recent human case of H5N1 in Texas is likely the first time a human has been infected with HPAI H5N1 from a cow (as opposed to birds)

The spread of the virus to cows was not only a new development—it was also unexpected. As it has moved from mammal to mammal, the virus has continually mutated or changed so that it can better spread.

Mammals—animals that produce milk—can become infected if they eat birds or other animals that have the virus. They can also get infected if they are in environments that are contaminated with HPAI H5N1.

The quick spread of the virus in a species—such as in tigers, farmed minks, and sea lions—may be due to one mammal passing it on to another mammal, instead of each mammal catching the virus from birds. However, this has yet to be confirmed.

Recently, a Reuters news article noted that migrating birds may have helped the spread of bird flu to dairy farms. As infected waterfowl, such as mallard ducks, move across the country, they may stop to get food and water from farms on the way. As they do so, the birds may spread flu on the farm through their saliva and feces. The contaminated saliva and droppings may be picked up on workers’ booths or farm equipment, passing on the virus to farm birds—or farm birds may come into direct contact with the contaminated saliva and feces.

Researchers in Kansas and Germany have investigated how this virus is spreading among dairy cows. The results from their experiments, which have yet to be published in a scientific journal, indicate that dairy cows may be infected with the virus from contaminated milking machines.

In birds, HPAI H5 viruses, such as HPAI H5N1, are often deadly. H5N1 can spread quickly in birds. Death rates in chickens are as high as 90% to 100%, and can occur within 48 hours of infection.

The effects that HPAI H5N1 has in other animals can vary. According to a New York Times article, the virus killed over 30,000 sea lions in Peru and Chile throughout 2022 and 2023; in October 2023, it killed more than 17,000 elephant seals in the Eastern Patagonia, located in Argentina.

Estimates suggest that since March 2024, HPAI H5N1 has infected 132 herds of dairy cows in 12 states. Most cattle infected with HPAI H5N1 have had mild symptoms, such as digestive issues, fever and reduced appetite; they also produce less milk. Most cows are able to get well again. However, as of June 2024, Reuters reported that infected dairy cows in five states either died or were slaughtered because they were unable to recover from the virus. 

People who have been infected in the United States since 2022 have had various symptoms, such as fatigue, conjunctivitis (irritated or inflamed eyes), or coughing. The four earliest cases were isolated and treated with an antiviral drug, and were later reported to have recovered from their illness, or to be in the process of recovery.

Before the spread of HPAI H5N1 in recent years, the severity of avian flu symptoms has ranged from no symptoms or mild symptoms to severe illness, such as pneumonia that needed hospitalization.

Generally speaking, the more common symptoms of avian flu have included a fever of 100◦F or higher, cough, sore throat, runny or stuffy nose, muscle or body aches, headaches, fatigue, and shortness of breath or difficulty breathing. The less common signs of avian flu include diarrhea, nausea, vomiting, or seizures.

Since 2003, HPAI H5N1 has been found in almost 900 people worldwide. About 50% of those people with known infection died. 

There have been no reports of human-to-human transmission of avian flu in the United States. However, since HPAI H5N1 was detected in humans in 1997, there have been a few cases of avian flu in people that are considered to have spread from other people.

In 2022 and 2023, egg shortages due to the deaths of tens of millions of chickens, caused by HPAI H5N1, resulted in price increases.

Aside from this, the virus has since been detected in raw dairy milk, so people should avoid drinking raw milk. A recent study of pasteurization processes commonly used in commercial milk processing found that these processes were effective at inactivating H5N1 in raw milk samples.

In addition, according to the U.S. Department of Agriculture (USDA), no meat from affected dairy cattle has entered the food supply.

There are many activities that are taking place on local, state and national levels. Here is a brief summary of what’s been happening so far.

In animals—The USDA’s Animal and Plant Health Inspection Service (APHIS) is working with states and the poultry industry to help protect birds against avian flu—and to help control it. This includes birds that are part of commercial flocks, as well as household flocks and live bird markets.

As part of its work, the USDA APHIS coordinates programs and supplied resources to states as they work to limit the spread of the virus. It also works with U.S. states, tribal and industry groups by coordinating actions to contain and eliminate avian flu when it is found. Additionally, the government agency works with the Department of Homeland Security to monitor illegally smuggled poultry and poultry products. It has also placed trade imported poultry and poultry products from countries and areas that have been affected by HPAI H5N1. Live birds are quarantined and tested for avian flu before they enter the United States (although live birds from Canada are allowed to enter the country without quarantining and testing, but require certain permits for entry).

In April 2024, the USDA APHIS also issued a federal order for mandatory HPAI H5N1 testing of dairy cattle that are being moved between state lines.

In humans—Since February 2022, the CDC and state and local health departments have monitored people who have had exposure to birds or other animals. Since March of 2024, that monitoring has extended to people who have been exposed to cattle that have avian flu. As of early August 2024, at least 4,300 people who have been exposed to HPAI H5N1 have been monitored for symptoms of avian flu.

In addition, the CDC is working to increase awareness and supporting protection programs related to the virus among farm workers, who are at greater risk of infection than others. On July 30, 2024, the CDC announced in a press conference that it is spending $5 million to provide seasonal flu vaccines to farm workers. Although the seasonal flu shot does not protect people from avian flu, it could reduce the chances that farm workers get the seasonal flu and HPAI H5N1 at the same time. If people were co-infected with these two different flu viruses, that might result in new flu virus mutations that result in new flu strains. The CDC is also dedicating another $4 million to help the National Center for Farmworkers Health and other organizations in educating farm workers about HPAI H5 and how to protect themselves from it.

Within the general population, the CDC has several systems in place to watch over possible signs of flu—including avian flu. These include reviewing case reports of flu, clinical lab trends and public health lab reporting on cases of flu. The CDC also monitors wastewater for evidence of flu, as well as emergency department visits for unusual trends due to possible flu.

Pre-pandemic planning—Although the risk that HPAI H5N1 poses to humans is low, the U.S. government has a plan in place to help protect public health in the event of a widespread outbreak. This plan involves the Biomedical Advanced Research and Development Authority (BARDA), which is part of the U.S. Department of Health and Human Services.

BARDA works to develop medical countermeasures—such as technologies or products such as vaccines, treatments and diagnostic tools—for medical emergencies that threaten public health. As HPAI H5N1 continues to spread, BARDA has contracted work on creating doses of a pre-pandemic H5N1 flu vaccine.

There isn’t any data from randomized clinical trials that provide information on antivirals on new influenza A viruses, such as H5N1. However, in observational studies of people with various types of flu—including HPAI H5N1—results showed that early treatment can reduce the severity of any flu-related complications, and that it also can reduce the rates of death.

So far, the virus has infected people who have had close, extended and unprotected contact with infected birds or other animals. The best way to avoid getting avian flu is by avoiding any sources of exposure.

The CDC has provided details on how people can limit their risk of HPAI H5N1. Their recommendations include:

•  Avoid or limit direct contact with or exposure to wild birds

•  Avoid unprotected contact with domestic poultry or other animals that may be sick, have died, or may have had avian flu. Wear personal protective equipment (PPE), such as gloves and a mask, during contact

•  Avoid touching surfaces that may be contaminated with substances, such as saliva, droppings or raw milk, from birds or other animals that may be infected

•  Drink only pasteurized milk and avoid raw milk

•  Cook poultry, eggs and beef thoroughly so they reach temperatures that kill bacteria and viruses

There are also specific guidelines that the CDC has created for people who come into contact with birds as part of their jobs, as well as hunters, bird owners, and people who have backyard flocks of birds. Read the CDC’s full set of recommendations and guidance for people here.