Avian influenza is a problem that affects in most of the cases the birds. This type of infection is caused by the bird flu viruses also called avian influenza viruses. These viruses are common among birds. Wild birds carry these viruses in their intestines but they never get affected by these viruses. Wild birds are only able to spread the virus that is usually caught by the domesticated birds including chickens, ducks or turkeys. The domesticated birds are affected and their internal organs are weakening which may lead to death.

The infected birds carry the virus in their saliva, nasal secretions or faeces. After any contact with an infected surface the domesticated birds may become infected too. Water also helps the spreading of the virus as much as dirt or cages or feed.

Bird flu can affect the domestic birds in two different ways. The first possibility is that the virus to go undetected and to cause rare and mild symptoms such as falling feathers or low egg production. This first possibility is the easy way. The highly pathogenic form spreads more rapidly and has more severe effects than the first form. This form usually causes the multiple internal organs failure and may lead to death.

We know many subtypes of bird flu viruses, more exactly of A influenza viruses. These subtypes differ because of the changes of protein levels on the surface of the influenza A virus, hemagglutini HA and neuraminidase NA proteins. There are 16 HA subtypes and 9 NA subtypes of influenza A viruses. There are available many combinations between HA and NA proteins. Each of these combinations represents a different subtype. All of these possible combinations can be seen in birds.

Avian influenza virus or bird flu virus refers in most of the cases to birds. Even so these infections may occur in humans too. The risks of developing avian influenza are low in humans. That is why during the last years we only noticed a small number of cases. The first case was reported in 1997 in Hong Kong during the bird flu pandemic. Humans might capture the virus after getting in contact with the affected birds or with contaminated surfaces or materials.

Among humans there are known only three subtypes of influenza viruses: H1N1, H1N2 and H3N2. Influenza A H5N1, one of the most dangerous viruses usually do not affect people. Even so we saw some cases during the time. These cases were the result of getting in close contact with the infected poultry or contaminated surfaces.