A person in Texas is being treated for avian influenza (bird flu), according to a report from state officials. The deadly virus has sickened dairy cows in five states in recent weeks.

This marks the first known instance globally of a person catching the H5N1 strain of bird flu from a mammal and just the second human case of the illness in the United States, according to the Centers for Disease Control and Prevention (CDC). An individual who had contact with infected poultry caught the virus in 2022.

Dean Blumberg, chief of pediatric infectious diseases at UC Davis Health, answers questions about what you need to know about bird flu.

What is bird flu?

Bird flu is caused by influenza strains that commonly infect wild birds worldwide. They can also cause outbreaks among commercial or backyard poultry, and less commonly other animals.

What are the symptoms of bird flu?

Bird flu may cause birds to have respiratory symptoms such as a runny nose and coughing or sneezing, diarrhea, less energy, decreased egg production, or sometimes sudden death.

In humans, bird flu may cause illnesses similar to influenza (the flu) with fever, cough, sore throat, runny nose and muscle aches. Less commonly, humans may have diarrhea and vomiting, and more rarely, seizures.

How is bird flu typically spread?

Most infections occur when humans have contact with sick or dead infected animals without wearing personal protective equipment.

How can cows get bird flu?

Many different bird species may be infected with bird flu, and the infectious virus is shed in their saliva, mucous and feces. The shed infectious virus may then infect other animals, including cows.

Is bird flu contagious person-to-person?

Bird flu rarely spreads person-to-person. It is more commonly spread from animal to human. There has been no evidence of sustained human-to-human spread.

Is it possible that bird flu has evolved in ways that would help it spread more easily among humans?

There is no evidence bird flu is currently more easily spread human-to-human, although there is always a chance the virus may evolve to more easily transmit among humans. Most human infections with bird flu can be traced to unprotected close contact with ill or dead animals.

Should people avoid eating beef or ingesting dairy products?

Sick or ill animals should be culled, and their animal products should not be sold. Pasteurization will kill infectious virus in contaminated milk. There may be a risk of transmission if unpasteurized milk from an ill animal is ingested.

How is bird flu treated in humans?

Bird flu is treated similarly to influenza in humans. The antiviral oseltamivir (Tamiflu) remains an effective option to treat humans infected with bird flu.

How can people protect themselves to prevent bird flu?

Avoid unprotected exposures to sick or dead animals. This includes birds, poultry or other animals. For those who work with animals, full personal protective equipment should be used when in close or direct contact with animals or material that is potentially contaminated with the virus. This includes an N95 mask or equivalent, goggles, gloves, gown, head cover and boot covers.