Medical expert of the article
New publications
Avian flu - Symptoms
Last reviewed: 04.07.2025
All iLive content is medically reviewed or fact checked to ensure as much factual accuracy as possible.
We have strict sourcing guidelines and only link to reputable media sites, academic research institutions and, whenever possible, medically peer reviewed studies. Note that the numbers in parentheses ([1], [2], etc.) are clickable links to these studies.
If you feel that any of our content is inaccurate, out-of-date, or otherwise questionable, please select it and press Ctrl + Enter.
The incubation period of bird flu (influenza A (H5N1)) is 2-3 days, ranging from 1 to 7 days.
Bird flu has an acute onset. Symptoms of bird flu are observed, which are expressed in severe intoxication. The body temperature from the first hours of the disease rises to 38 ° C, often reaching hyperpyretic values. The febrile period is extended to 10-12 days, and in severe cases with a fatal outcome - until the last hours of the patient's life. Chills, muscle and joint pain are characteristic. At the height of the disease (2-3rd day), such symptoms of bird flu as catarrhal syndrome are added, manifested by the development of bronchitis, bronchiolitis, laryngitis; there may be signs of rhinitis. Sore throat and "flaming" oropharyngitis are characteristic. During this period, most patients develop primary viral pneumonia. In this case, shortness of breath, a wet cough with sputum, possibly with an admixture of blood, appear. Hard breathing, moist wheezing of various sizes, and crepitation are heard over the lungs.
On the chest X-ray in the early stages, non-specific changes are determined in the form of diffuse, multifocal or individual infiltrates, which tend to spread and merge rapidly. In some cases, segmental or lobar consolidations can be detected. Progressive course, increasing dyspnea and development of respiratory distress syndrome are characteristic.
Along with intoxication and catarrhal syndrome, gastrointestinal tract damage develops, manifested by repeated vomiting, secretory diarrhea and abdominal pain. Liver enlargement is possible, accompanied by increased activity of serum transferases. Acute renal failure and creatininemia develop in a third of patients. Signs of damage to the nervous system are determined in most patients, disturbances of consciousness and development of encephalitis are possible.
The hemogram shows leukopenia, lymphopenia, and thrombocytopenia.
There may be variants of the course of the disease with fever, diarrhea and no signs of damage to the respiratory organs.
[ Complications of bird flu
Bird flu is dangerous due to the development of viral pneumonia, damage to the kidneys, liver, and blood-forming organs. It is these consequences that often lead to the death of patients. It has been established that the place of replication of the H5N1 influenza virus in humans (at least in those who died as a result of the disease) is not only the respiratory tract, but also the intestines.
Risk factors for developing severe forms of influenza A (H5N1) in humans:
- the patient's age (in children five years of age and younger, the symptoms of the disease are not clearly expressed);
- duration of the disease manifestation before hospitalization (delay from hospitalization);
- anatomical level of respiratory tract damage;
- degree of leukopenia in peripheral blood;
- the presence of multiple organ dysfunction.
Mortality and causes of death
Bird flu has a high mortality rate, which is 50-80%. Most often, patients die from complications in the second week of the disease.