The Romanian Ornithological Society

The avian influenza (AI) is an infectious disease caused by the influenza virus. The influenza viruses that constitute this family are classified into types A, B or C. AI viruses belong to type A, which has been isolated in domestic and wild poultry. Type A is also divided into several subtypes; some of them are moderate but others are extremely pathogenic (they can cause 100% mortality). The most pathogenic forms are H5N1 and H5N3, the first one being identified in human infections. The AI virus can be found naturally in wild bird species, but the virulence of most of its forms is reduced (meaning that infected birds do not get sick). The birds become ill very rarely and only when pathogenic forms are present. Usually these epidemics end quickly because the sick birds die fast without spreading the disease in large territories. The pathogenic forms (like H5N1) appeared in overcrowded poultry farms, especially in those places where hygiene was not strict. The disease (and the pathogenic forms of the virus) spread much faster in poultry farms or when the birds (or related products) are transported.

The transmission of H5N1 form from free wild birds to humans could not be proven until now. Normally the virus is spread only among birds, but occasionally a virulent strain may emerge by genetic mutation and can affect people or other animals. AI in humans is caused by prolonged contact with sick animals (in crowded poultry farms) or by consuming infected birds that were not properly cooked. It is a well-known fact that this virus is destroyed at 70 º temperatures; thus consuming cooked chicken does not theoretically imply any risks.

Although all the causes of the virus's spread are not known, we can identify some of them: lack of hygiene in poultry farms, the transport and selling of live poultry and derived products (meat, eggs), the movement of people and vehicles between poultry farms, the selling wild birds in markets and bird migration, especially ducks, geese and gulls. Up to the present the only place where we can exclude spreading from poultry to wild birds (and virus transportation by migratory wild birds) is Qinghai Lake in China.

More often the disease is visible in poultry, but occasionally wild birds can get sick too. The most susceptible birds are the ones kept in tight spaces on farms. Ducks (Anatinae) don't usually die of AI but they carry the virus. The pathogenic form (H5N1) of the virus has been identified in 11 species of wild birds, but only in East Asia and Africa. Some of these species (the mallard - Anas platyrhynchos, the cormorant - Phalacrocorax carbo and the common tern - Sterna hirundo) migrate and they could carry the virus over long distances. These species are common in Romania too, but the migratory populations in our country do not meet with the ones in East Asia. Until now the virus has caused epidemics in some species of wild birds only on three occasions. In 1961 there was a case of mass mortality among the common terns in South Africa but the H5N3 form of the virus caused it. In May 2005 wild birds in Qinghai Lake area from China developed symptoms, and more recently there were some cases in the north-east of Mongolia.

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