Avian influenza, commonly known as bird flu, is a disease caused by influenza viruses originating in birds. These viruses of the Orthomyxoviridae family include A(H5N1) but also other influenza viruses of avian origin. They primarily affect birds but have also been detected in mammals, including bovines. Bird flu rarely affects humans, but people should stay informed and take the recommended preventive measures.
The most common way for the virus to enter a territory is through migratory wild birds. The main risk factor for transmission from birds to humans is direct or indirect contact with infected animals or with environments and surfaces contaminated by feces or other fluids. Plucking, handling infected poultry carcasses, and preparing poultry for consumption, especially in domestic settings, may also be risk factors.
Symptoms range from mild (even asymptomatic) to severe. Reported symptoms include fever, cough, cold, conjunctivitis, gastrointestinal symptoms, and respiratory issues.
Antiviral medicines are recommended for those with severe diseases or at risk of developing severe illness due to underlying conditions (e.g., older adults or individuals with chronic health issues). People who experience bird flu symptoms should contact their healthcare provider to receive the appropriate treatment.
Whenever there is exposure to infected animals (such as poultry, wild birds, or mammals) or contaminated environments where avian influenza viruses circulate, there is a risk of sporadic human infection.
Human cases of avian influenza associated with this A(H5N1) are isolated. Seventy A(H5N1) human infections have been reported in the Region of the Americas: 67 in the United States (as of April 2022), one in Ecuador (January 2023), one in Chile (March 2023) and one in Canada (November 2024), with one death associated with A(H5N1) infection in the United States. Mostly linked to livestock (40 cases, all in the United States) or poultry contact, five cases could not identify the source of exposure. Human-to-human transmission was not identified in any of these cases.
Humans don’t have prior immunity to avian influenza, so it can cause serious illness. However, it is challenging to generalize based on historical data because the virus is evolving. Infections in humans have ranged from mild to severe. Since 2003, about 900 human cases of A(H5N1) infection have been reported, with a death rate of over 50%.
The World Health Organization (WHO) regularly updates potential vaccine candidates to be prepared for pandemics. This helps ensure vaccines can be quickly produced if needed. For the H5N1 virus found in dairy cows, WHO already has potential vaccines ready through its Global Influenza Surveillance and Response System (GISRS).
Milk and Food Safety
High amounts of the A(H5N1) virus have been found in raw milk from infected herds. The role of milk consumption and handling in transmission is being investigated.
Dairy products made from safe milk, following strict hygiene standards, should be safe to consume. The World Health Organization (WHO) and the Food and Agriculture Organization (FAO) strongly advise consuming pasteurized milk, as pasteurization is effective against avian influenza and other pathogens. Studies by the Food and Drug Administration (FDA) on pasteurization have shown promising results.
Note: some commercial pasteurized milk samples in the US have been found to contain virus fragments, which returned “PCR positive” test results. As long as the milk only contains virus fragments (as is the case here) and not live or infectious virus, it should be safe to consume. A positive PCR result does not necessarily indicate that the virus or parts of the virus detected will cause illness.
For dairy workers, activities involving handling of milk from infected herds, such milking cows or cleaning the milking parlor, may increase their chance of infection. Therefore, they should follow the recommended preventive measures.
Yes, this is the first instance of avian flu being detected in milk and the first large-scale event affecting multiple cow herds, though past cases of infection in cattle have been documented.
Dairy products made from pasteurized milk and following strict hygiene standards are considered safe. For raw milk cheese, the survival of the virus during production is under investigation. As a precaution, production of raw milk cheese in outbreak areas is not recommended.
Has meat been affected? Is it safe to eat meat from affected animals?
No detections have been reported in beef herds. WHO advises thorough cooking of meat to reduce exposure to pathogens.
Specific Animal Risks
Countries need to have a thorough, updated contingency plan for outbreaks. Specific recommendations for these plans can be obtained from organizations such as the Food and Drug Administration (FAO) and the World Organization for Animal Health (WOAH). Teams involved in surveillance and response to animal influenza must be trained to implement these plans in case of emergency and should be provided with the necessary resources to do this.
It is also key that poultry producers reinforce biosecurity in their facilities, preventing contact between domestic poultry and wild birds, including through water and feed.
Farmers also play a key role in the early detection of the disease and need to be able to recognize and report it to the veterinary authorities so that avian influenza can be ruled out or confirmed and appropriate action taken. Early detection facilitates a timely response, thus helping to reduce the spread of the virus. Individuals or families keeping birds for personal consumption should also be well informed on how to recognize an infected bird, what measures to take, and how to protect themselves adequately.
Visit the Pan American Center for Foot-and-Mouth Disease and Veterinary Public Health (PANAFTOSA) webpage.
Cats are susceptible to H5N1, including pet cats and wild animals like tigers, lions, and leopards. Risk factors for cats include exposure to sick or dead birds, consuming infected raw poultry, or drinking raw milk. Infected cats may develop severe symptoms and even die.
Studies suggest people can transmit seasonal influenza viruses to cats, but human risk from infected cats is currently considered low. The World Health Organization (WHO) advises avoiding contact with sick or dead animals and practicing hygiene when handling pets.
Cases have only been reported in the US, but given livestock trade and global virus spread, surveillance is essential. Some countries have tested milk and blood samples without detecting the virus. WHO encourages strategic surveillance of farm animals and people working in the sector.
Surveillance and Lab
Adequate surveillance for the presence of avian influenza in animals, including birds and mammals, provides information about which subtypes of influenza are in circulation. It also enables to detect the presence of viruses with a more marked zoonotic character, i.e. possibly presenting genetic changes that can result in greater adaptability for transmission from humans-to-humans, which is important for public health.
Early detection also allows countries to implement rapid response actions to mitigate the risk of virus transmission to humans.