H5N1 is a type of influenza virus that causes a highly infectious, severe respiratory disease in birds called avian influenza (or “bird flu”). Human cases of H5N1 avian influenza occur occasionally, but it is difficult to transmit the infection from person to person. When people do become infected, the mortality rate is about 60%.
Almost all cases of H5N1 infection in people have been associated with close contact with infected live or dead birds, or H5N1-contaminated environments. The virus does not infect humans easily, and spread from person to person appears to be unusual. There is no evidence that the disease can be spread to people through properly prepared and thoroughly cooked food.
The symptoms of H5N1 infection may include fever (often high fever, > 38°C) and malaise, cough, sore throat, and muscle aches. Other early symptoms may include abdominal pain, chest pain and diarrhoea. The infection may progress quickly to severe respiratory illness (for example, difficulty breathing or shortness of breath, pneumonia, Acute Respiratory Distress Syndrome) and neurologic changes (altered mental status or seizures).