The H5N1 Avian influenza is decimating bird populations around the world. More than 136 million birds have been affected in the US since the disease arrived in 2022. More than 5 million egg-laying chickens died in the first 16 days of 2025. It also shows signs of mutating to become more infectious to mammals. The disease has shown up in dozens of cats, zoo animals, people and more than 900 dairy herds.
David J. Cennimo, an associate professor of medicine and pediatrics in the Division of Infectious Diseases at Rutgers New Jersey Medical School, spoke to Rutgers Today about what people should know about the disease and its likely course going forward.
What is bird flu?
Avian influenzas, commonly called "Bird Flu," are influenza viruses that readily infect and spread through birds. While multiple influenza viruses are known, the H5N1 bird flu is the most widely circulating at present and is the main cause of concern for possible human transmission. This virus is similar to human-adapted influenza currently circulating (H1N1 and H3N2) but, to date, has not infected many humans or transmitted from human to human.
How many people have been infected so far?
Fewer than 100 human cases have been reported. Of those, the majority had close contact with sick birds. More recently, infections in dairy herds have become more common with secondary human infection from infected cows. There are also case reports of other mammals becoming infected. In general, infections in other mammals are more concerning because, being generically more similar to humans, the virus could be adapting and becoming more infectious for humans.
How have people become infected?
Infections have been acquired from contact with sick animals, including droppings.
Should people be worried about eating poultry, eggs and even beef?
There is no known risk from eating poultry or eggs because cooking kills the virus. There has been reports of sick cats who are believed to be infected from raw chicken pet food. Avian flu has been found in milk from infected cows, but pasteurization has been shown to inactivate it. It is unknown if unpasteurized milk can transmit infection.
Who is at risk of being infected?
So far, it's been entirely confined to people working with sick animals or raw animal byproducts. As with human influenza, the most susceptible to severe infection are people at the extremes of age and with co-morbidities. To date, we have not seen human-to-human transmission of avian influenza. This is closely monitored as it would indicate a possibility for a sustained outbreak.
How do you know if you're infected?
Symptoms include fever, cough, upper respiratory infection, as with all influenza. The case reports do mention an increased prevalence of conjunctivitis as a common symptom that may be mistaken for other viral infections.
How can people protect themselves?
People should avoid contact with sick birds or livestock and use personal protective equipment if contact is unavoidable. Thoroughly cooking food and pasteurizing milk reduce the risk of many infections, including H5N1.
