Avian flu (avian influenza, bird flu) is a disease caused by the influenza virus subtypes H5N1, H7N9, and H9N2.
The influenza virus subtypes H5N1, H7N9 and H9N2 are spread among birds, people get infected via direct contact with infected birds. While seasonal influenza is known to affect younger and older generations, avian flu has the highest incidence among those aged 10-40 years. Avian flu is considered more severe in comparison to normal influenza, it is associated with higher mortality. Luckily, it is not so easy to catch avian flu. The virus has a high affinity to the lower respiratory tract so there is only a slight risk of its spread by the air droplets. Nevertheless, it is recommended to avoid visiting the outbreaks areas and a person should stay away from deceased or sick poultry. When such contact is unavoidable a person should wear a protective respiratory mask, gloves and safety glasses.
The influenza virus is a negative-sense RNA virus. There are three strains of the virus – A, B and C. Avian influenza virus belongs to group A. Once being inhaled, the virus binds with the respiratory epithelium, enters the cell and starts reproducing, at the same time damaging the airways.
There were approximately 1000 cases of avian flu reported since 2000. Recently cases of bird flu were reported in the Middle East, China, Taiwan, Hong Kong and some parts of Africa.
Children and young adults are considered especially susceptible to the avian influenza virus and in general tend to experience more severe course of the disease.
Individuals who were exposed to sick, dying or dead poultry or products made of poultry are at risk of contracting the disease. However, there were some reports about cases when a human got infected after being exposed to asymptomatic poultry.
Normal influenza spreads widely during the epidemic season, whereas avian flu remains relatively rare. This can probably be explained by the fact that avian flu in confined to the lower respiratory tract, and, thereby, it cannot be spread so easily as normal influenza, although exposure to sick humans is also a significant risk factor and background for the pandemics.
The incubation period lasts from several hours up to 7 days (with average of 2-5 days).
Unlike regular influenza, avian flu affects lower parts of the respiratory tract and is associated with more severe course of the disease.
Symptoms of the disease include:
- Cough, sometimes with bloody sputum;
- Rapid breathing and heart rate;
- Fever (temperature over 100ºF or 37.8ºC);
- Watery stool;
- Abdominal or chest pain, headache;
- Consciousness disturbances due to brain inflammation (encephalitis);
- Sore throat;
- Runny nose;
Avian flu may be suspected when there is a history of exposure to sick or dead birds or humans suffering from avian influenza.
Blood testing might show leukopenia (low white blood cell count) with a higher fraction of lymphocytes.
A chest X-ray should be performed. Typically multiple lesions of the lungs will be seen suggesting viral pneumonia.
PCR helps to detect viral RNA and confirm the strain of the influenza virus.
Antiviral medications (oseltamivir, amantadine) are the backbone of avian flu treatment. The treatment should be started as soon as possible to provide better outcomes. Later in the course of disease antibiotics may be also necessary if there is the accompanying bacterial infection.
Avian flu is associated with high mortality – about 30-60% of infected individuals eventually die.
Unfortunately, there is no available vaccine against avian flu.
It is recommended to avoid traveling to regions where outbreaks of avian flu were reported, avoid contact with poultry and eat only finely processed meat.