Bird flu, also known as avian influenza, is a viral infection that primarily affects birds but can occasionally infect humans and other animals1 . Since 2003, about 900 human cases of avian influenza A(H5N1) have been reported worldwide, with symptoms ranging from mild respiratory illness to severe complications including pneumonia and neurological issues2 3. Human infections are rare and usually occur after close contact with infected birds or animals, with symptoms typically developing within 2 to 10 days after exposure3 4.
Common Bird Flu Symptoms
Bird flu symptoms in humans often resemble those of seasonal influenza, involving respiratory and systemic signs5 4. The severity of illness can vary widely, from mild discomfort to severe respiratory distress6 .
Fever
Fever is a frequent early symptom of bird flu infection, defined as a body temperature exceeding the normal baseline, typically above 38°C (100.4°F) 57. It is often accompanied by chills and can signal the body's immune response to the virus8 . However, fever may not be present in all cases5 .
Sore Throat
Sore throat and throat irritation are common early symptoms of bird flu5 . The severity ranges from mild discomfort to intense pain, which can worsen with speaking or swallowing, sometimes causing difficulty eating or drinking5 8.
Upper Respiratory Symptoms
Upper respiratory tract symptoms are typical in bird flu infections and include cough, nasal congestion, and nasal discharge8 . In severe cases, patients may experience dyspnea (difficulty breathing) and shortness of breath, which can indicate pneumonia or other serious respiratory complications requiring urgent medical care5 8. Progressive symptoms such as chest pain and fatigue may suggest lower respiratory tract involvement9 .
Aches, Fatigue, and Malaise
Bird flu patients often report muscle aches, headaches, and general fatigue, similar to seasonal influenza6 4. These systemic symptoms reflect the body's response to viral infection and can contribute to overall malaise.
Pink Eye (Conjunctivitis)
Eye redness or conjunctivitis has been a predominant symptom in recent human cases of bird flu in the United States6 4. The virus can infect the conjunctiva (the membrane covering the eye), leading to irritation and redness4 . Swabs from the conjunctiva may be used for diagnostic testing when eye symptoms are present4 .
Bird flu symptoms in humans often mimic seasonal flu but can include unique signs such as conjunctivitis, which has been prominent in recent U.S. cases. Early recognition of these symptoms is crucial for timely diagnosis and treatment. 46
Less Common Human Symptoms
Besides respiratory and systemic symptoms, bird flu can occasionally cause gastrointestinal symptoms such as diarrhea, nausea, and vomiting5 . Diarrhea is characterized by frequent loose or watery stools, typically three or more times daily, often accompanied by abdominal cramps and urgency to defecate5 7. Nausea involves an unsettled stomach with an urge to vomit7 . These symptoms are less frequent but important to recognize as part of the clinical spectrum of avian influenza5 .
Rare Human Symptoms
Neurological complications are rare but serious manifestations of bird flu infection2 . These can include encephalitis (inflammation of the brain) and myelitis (inflammation of the spinal cord) 2. Patients may experience dizziness, cognitive difficulties, headaches, seizures, or even coma in severe cases2 . Such complications require urgent medical attention and intensive care3 .
“Severe avian influenza may cause respiratory failure and neurological complications, highlighting the need for early diagnosis and treatment to improve outcomes.”
— Pokhrel et al. 2
Bird Flu Symptoms in Poultry
In birds, symptoms of avian influenza vary widely, ranging from asymptomatic infection to sudden severe illness and high mortality10 11. Some birds may carry the virus without showing signs, posing a risk for transmission to other animals and humans12 . Symptomatic birds often exhibit respiratory distress, swelling of the head and face, and sudden death11 . Recognizing these signs in poultry is critical for controlling outbreaks and preventing human exposure11 .
When to Seek Medical Care
Early antiviral treatment with drugs like oseltamivir can improve outcomes in bird flu infections, underscoring the importance of prompt diagnosis and medical care. 48
Prompt medical evaluation is advised for anyone with symptoms suggestive of bird flu who has had potential exposure to infected birds or animals3 . Early testing, ideally within the first few days of symptom onset, improves diagnostic accuracy and allows timely antiviral treatment3 4. Emergency care is necessary for severe symptoms such as respiratory distress, seizures, or signs of severe dehydration, including markedly reduced urine output and dark-colored urine3 .
Exposure to infected birds or animals should be reported to public health authorities for monitoring and containment3 11. Individuals with mild symptoms should still seek medical advice to prevent progression and reduce transmission risk3 .
- Notify health departments if exposed to infected birds or animals3 11.
- Seek medical evaluation if symptoms develop within 2 to 10 days after exposure3 .
- Emergency care is needed for difficulty breathing, seizures, or severe dehydration3 .
- Early antiviral treatment improves outcomes8 4.
- Use personal protective equipment when handling sick or dead birds4 .
Bird Flu Symptoms Summary
Bird flu in humans typically begins with fever, sore throat, and upper respiratory symptoms such as cough and nasal congestion5 8. Fatigue, muscle aches, and pink eye are also common6 4. Less commonly, gastrointestinal symptoms like diarrhea and nausea may occur5 . Rarely, neurological complications such as encephalitis and seizures develop2 . In birds, symptoms range from none to sudden death with respiratory distress and swelling11 . Early recognition and medical care are essential to manage the disease and prevent severe outcomes3 .
| Symptom Category | Common Symptoms | Less Common Symptoms | Rare Symptoms |
|---|---|---|---|
| Respiratory | Fever, cough, sore throat, nasal congestion, dyspnea5 86 | — | Respiratory failure2 |
| Systemic | Fatigue, muscle aches, headaches6 4 | — | — |
| Ocular | Pink eye (conjunctivitis) 64 | — | — |
| Gastrointestinal | — | Diarrhea, nausea, vomiting5 | — |
| Neurological | — | — | Encephalitis, seizures, coma2 |
Bird Flu FAQ
What causes bird flu in humans?
Bird flu is caused by influenza A viruses, primarily subtypes H5N1 and H7N9, which usually infect birds but can occasionally infect humans through close contact with infected animals or contaminated environments1 4.
How common are human infections?
Human cases are rare, with about 900 cases reported globally since 2003. Most infections occur in people exposed to sick or infected birds or animals3 2.
What are the typical symptoms in humans?
Symptoms often resemble seasonal flu, including fever, cough, sore throat, and fatigue. Eye redness and gastrointestinal symptoms are less common. Severe cases may involve pneumonia and neurological complications5 26.
Can bird flu spread from person to person?
Human-to-human transmission is extremely rare and has not been documented in recent U.S. outbreaks3 4.
How is bird flu treated?
Antiviral medications such as oseltamivir are recommended, especially when started early. Supportive care and hospitalization may be required for severe cases8 4.
