Bird flu looks different depending on who’s infected. In people, the most common sign in recent U.S. cases has been red, irritated eyes, often alongside mild fever and cough. In poultry, it can cause sudden death, purple discoloration of the head and legs, and swelling around the face. In dairy cows, the telltale sign is thick, discolored milk and a sharp drop in production. Here’s what to watch for across species.
Symptoms in People
Eye redness and irritation (conjunctivitis) has been the predominant symptom among recent U.S. human cases of H5 bird flu, according to the CDC. That’s a notable departure from what most people expect. Rather than starting with cough and body aches like seasonal flu, bird flu in humans often shows up first in the eyes, particularly in people who had direct contact with infected animals.
Beyond the eyes, mild cases can include:
- Low-grade fever (100°F / 37.8°C or higher)
- Cough and sore throat
- Runny or stuffy nose
- Muscle or body aches
- Headaches and fatigue
These symptoms overlap heavily with regular flu or a bad cold, which makes bird flu easy to miss without lab testing. What sets it apart is context: if you’ve recently been around poultry, wild birds, or dairy cattle and develop red eyes with flu-like symptoms, that combination is worth taking seriously.
When Symptoms Turn Severe
Most recent U.S. cases have been mild, but bird flu can progress to dangerous illness. Severe cases involve high fever, shortness of breath or difficulty breathing, altered consciousness, and seizures. The infection can cause viral pneumonia and respiratory failure, particularly with certain strains. Globally, H5N1 has carried a high fatality rate in sporadic cases over the past two decades, though the milder outcomes in recent U.S. dairy-worker cases suggest the strain and route of exposure matter significantly. As of late 2025, 71 confirmed human H5 cases have been reported in the U.S. since early 2024, with the WHO assessing the overall public health risk as low. No sustained human-to-human transmission has been detected.
What Bird Flu Looks Like in Poultry
In chickens, turkeys, and other domestic birds, highly pathogenic avian influenza can be devastating and fast. Some birds die suddenly with no visible warning signs at all. When symptoms do appear, they’re often dramatic and hard to miss:
- Swelling of the head, comb, eyelids, wattles, and hocks
- Purple or dark discoloration of the wattles, comb, and legs
- Nasal discharge, coughing, and sneezing
- Decreased egg production or soft-shelled, misshapen eggs
- Loss of energy and appetite
- Incoordination, stumbling, or inability to walk normally
- Diarrhea
The purple discoloration is one of the most recognizable visual signs. It results from poor blood circulation and tissue damage, and it often appears on the fleshy parts of the head and the legs. Combined with facial swelling and a sudden drop in egg laying, these are strong indicators that a flock may be infected. If you see multiple birds dying in a short period with these symptoms, contact your state animal health commission or the USDA immediately. For wild waterfowl, report clusters of five or more dead birds in one location to your state wildlife agency.
Signs in Dairy Cows
Bird flu jumped into U.S. dairy herds in early 2024, and the symptoms in cattle look nothing like what you’d see in birds. Infected cows become tired, lose their appetite, and eat less. The clearest sign is a sudden drop in milk production, with the milk itself turning thick and discolored, sometimes resembling colostrum (the dense, yellowish milk produced right after calving). Some cows develop mild fever, dehydration, clear nasal discharge, or slightly labored breathing. Calves may show respiratory symptoms and occasional diarrhea.
These symptoms are nonspecific, meaning they could point to several different cattle illnesses, which is part of why the virus circulated in herds for weeks before it was identified. Veterinarians and dairy workers now know to flag sudden, unexplained drops in milk quality and output as a potential sign of H5N1.
Signs in Cats and Other Mammals
Cats appear especially vulnerable, particularly after consuming raw milk or colostrum from infected cows. The disease hits their nervous system hard. Affected cats have shown depressed behavior, rigid body movements, loss of coordination, circling, blindness, and heavy discharge from the eyes and nose. Neurological exams of infected cats revealed absent blink and pupillary responses, indicating severe brain involvement. The illness in cats tends to be serious and often fatal, which is a sharp contrast to the mild symptoms seen in most human cases.
How Bird Flu Is Confirmed
You cannot diagnose bird flu from symptoms alone. Standard rapid flu tests at a doctor’s office can detect influenza A but typically cannot identify the specific H5 subtype. Confirming bird flu requires a swab from the nose, throat, or eyes, which is then sent to a public health laboratory for specialized testing. Some commercial labs, including LabCorp and Quest, now offer H5-specific testing as well. If you’ve had known exposure to infected animals and develop symptoms, let your healthcare provider know about the exposure so they can order the right test rather than a standard flu panel.