Human cases of bird flu, also known as avian influenza, are caused by influenza A viruses that normally infect birds. Sporadic human cases of bird flu have been reported since 1997. Most cases have occurred in Asia, caused by the H5N1 virus. Bird flu typically causes a severe and rapidly progressive illness in humans with a reported death rate of roughly 80 percent.
Fever and Chills
Almost all people with bird flu have a high fever with chills. Temperatures are typically higher than 100.5 F.
Flu-like Symptoms
Initial symptoms of bird flu are much like seasonal influenza. Headache, body aches, runny or stuffy nose, extreme tiredness and sore throat are common symptoms.
Gastrointestinal Symptoms
Watery diarrhea is common with bird flu, a characteristic that distinguishes it from seasonal flu. Nausea, vomiting and abdominal pain may also be present. In some cases of bird flu, fever and diarrhea have been the only reported symptoms.
Respiratory Symptoms
A hallmark of bird flu is the rapid development of breathing difficulties, also known as respiratory distress. This symptom typically develops within five days of the onset of the illness. Chest pain, breathlessness, rapid breathing, hoarseness and cough are common. Almost all people with bird flu develop pneumonia. In a 2008 study of 127 patients hospitalized with bird flu, Dr. I.N. Kandun and his colleagues found 88 percent had cough and 84 percent had difficulty breathing at the time of admission.
Neurologic Symptoms
Some people with bird flu develop symptoms of encephalitis, which reflects inflammation of the brain. Possible symptoms include confusion, impaired judgment, drowsiness, weakness, clumsiness, irritability and a heightened sensitivity to light. Loss of consciousness and seizures may develop in the most serious cases.
Abnormal Bleeding
Abnormal bleeding, such as bleeding from the nose and gums, may occur with bird flu. This serious symptom is caused by disruption of the blood clotting system. In the most severe cases, spontaneous and uncontrollable bleeding may occur from any body surface or opening.
References
- World Health Organization: Avian influenza frequently asked questions
- "Lancet"; Factors associated with case fatality of human H5N1 virus infections in Indonesia: a case series; I.N. Kandun, M.D., M.P.H., et al.; August 2008
- World Health Organization: Avian influenza fact sheet
