Bird flu spreads to humans primarily through direct contact with infected birds, contaminated surfaces, or exposure to airborne particles containing the virus. Most human cases trace back to close, unprotected contact with sick poultry or, more recently, infected dairy cattle. The virus does not spread easily between people, which is why human cases remain relatively rare despite massive outbreaks in animals worldwide.
Direct Contact and Contaminated Surfaces
The most common route of infection is touching something that carries the virus and then touching your eyes, nose, or mouth. Infected birds shed the virus in their saliva, mucus, and feces, and all of these can contaminate feathers, bedding, equipment, cages, and soil. You don’t need to handle a visibly sick bird. Walking through a contaminated area or touching a surface where droppings have dried can be enough if you then touch your face.
The virus is remarkably durable outside a living host. At refrigerator temperatures (around 4°C/39°F), H5N1 can survive on stainless steel for roughly 40 days and on plastic surfaces for about 45 days. Even at room temperature, it persists for 3 to 5 days on hard surfaces. In wastewater at room temperature, the virus takes about 16 days to become fully inactive. This environmental toughness means contaminated boots, tools, clothing, and vehicles can carry the virus well beyond the immediate area of an outbreak.
Airborne Exposure on Farms and Live Markets
You can also catch bird flu by breathing it in. When infected birds flap, preen, or defecate, they release tiny droplets and dust particles loaded with virus into the surrounding air. Cleaning poultry houses, handling litter, or working in live bird markets stirs up contaminated dust that can reach the lungs or settle on the lining of the eyes and nose. This is why outbreaks among poultry workers tend to cluster around activities that generate airborne material in enclosed spaces.
Why the Virus Rarely Infects Humans
Bird flu viruses and human flu viruses latch onto different types of receptors in the respiratory tract. Human-adapted flu viruses prefer a receptor configuration found abundantly in the nose and throat, while avian flu viruses prefer a different configuration that is rare in the human upper airway but more common deeper in the lungs. This mismatch means avian flu viruses have a hard time establishing infection in people. When they do, the virus often lands deep in the lungs rather than the nose and throat, which also makes it harder to cough or sneeze out to someone else.
Genetic surveillance of H5N1 viruses circulating in animals confirms they still retain these avian receptor preferences, with no significant changes that would make the virus better at infecting human cells. In two severe human cases (one fatal case in Louisiana and one in Canada), researchers found minor genetic shifts toward mammalian adaptation, but those changes appeared to have occurred after the patients were already infected, not before. There is no evidence those altered viruses spread beyond those individuals.
The New Risk: Dairy Cattle
Since early 2024, H5N1 has been spreading through dairy herds in the United States, creating a transmission pathway that didn’t previously exist at scale. Milking infected cows is now considered one of the higher-risk activities because raw milk from acutely infected animals contains live virus. A dairy worker in Michigan tested positive for H5N1 after raw milk splashed into his eyes during milking.
What makes dairy farms particularly tricky is that some cows carry the virus without showing obvious symptoms. Workers can be exposed during routine milking without realizing the herd is infected. Of the 71 human H5N1 cases reported in the United States since February 2024, a significant share have been linked to dairy or poultry farm exposures. Two of those cases were fatal.
Pasteurized milk remains safe. The pasteurization process kills the virus. The risk applies to people who handle raw milk directly, particularly farm workers who may get it on their hands, clothing, or face.
Human-to-Human Spread
This is the question that concerns public health officials most, and so far the answer is reassuring. There is no evidence of human-to-human transmission linked to the current outbreak in the United States. Globally, limited person-to-person spread has been reported on rare occasions, typically between close household contacts caring for a sick family member. These small clusters have never sustained beyond a second generation, meaning the virus infected one person, possibly spread to a close contact, and stopped there.
For the virus to become capable of spreading efficiently between people, it would need to acquire mutations that shift its receptor preference toward human-type receptors and allow it to replicate well in the upper airway. Scientists continuously monitor circulating viruses for exactly these changes, and current strains have not made that jump.
Symptoms and Timeline
If you are exposed and become infected, symptoms typically appear about 3 days later, though the window ranges from 2 to 7 days. Eye redness and irritation can show up sooner, within 1 to 2 days of exposure. Many of the recent U.S. cases have been mild, presenting mainly as conjunctivitis (pink eye) in dairy and poultry workers.
More severe illness can include high fever, shortness of breath, altered consciousness, and seizures. Serious complications include pneumonia, respiratory failure, kidney injury, and inflammation of the brain. Globally, the H5N1 strain has historically carried a high fatality rate in confirmed cases, though the recent wave of milder U.S. cases suggests that many infections may go undetected, making the true severity rate difficult to pin down.
Treatment Options
Antiviral medications work against bird flu when started early. The same class of drugs used for seasonal flu is effective, and treatment is recommended as soon as infection is suspected rather than waiting for lab confirmation. For most patients, a 5-day course of oral antivirals is standard. Hospitalized patients may receive a combination of two antiviral drugs to reduce the chance the virus develops resistance during treatment. The virus is resistant to an older class of flu drugs (adamantanes), so those are not used.
Who Is Most at Risk
Your risk depends almost entirely on how much direct contact you have with potentially infected animals or their products. The groups facing the highest exposure include poultry farm workers, dairy farm workers (especially those involved in milking), people who raise backyard flocks, and anyone involved in culling operations during outbreaks. Hunters who handle wild waterfowl also face some risk, since wild ducks and geese are the natural reservoir for avian influenza and often carry it without appearing sick.
For the general public, the risk remains low. Cooked poultry and eggs are safe, as heat destroys the virus. Pasteurized dairy products pose no risk. The primary concern is occupational exposure, and protective equipment like goggles, respirators, and gloves significantly reduces transmission during high-risk farm work.