PLACE AND ROLE OF AVIAN INFLUENZA WITHIN THE INFLUENZA ENTITY

Starting from the principled similarity and possibilities of variation of the antigenic components (Figure 1) of type A influenza viruses ex tremely widespread in nature, the author discusses the role and import ance of avian influenza within the influenza entity. Based only the tw o external antigens, at present 14 haemagglutinin and 9 neuraminidase subtypes or serotypes are known (Table 1). The influenza viruses isola ted in Hungary, at the Veterinary Institute of Debrecen since 1969 are grouped by subtype and avian species in Table 2. Influenza studies co nducted in South China and Northern American suggest that waterfowl ac t as the natural reservoirs of influenza virus, which is explained by the high incidence of symptomless infection, the intestinal form, and by the aquatic origin of life. Although influenza viruses mostly persi st in the species to which they have adapted themselves, they may cros s the species barrier. With regard to the animal kingdom and humans, t his is most likely to occur in South China, a region considered to be an influenza epicentre, where the transmission of influenza viruses fr om waterfowl to men most probably takes place through pigs, after much variation (Figure 2 and Table 3). Namely, in that region the close co existence of the three species, the high density of the human and anim al population, the optimal climatic and geographic conditions and the existing high susceptibility create a possibility for a chain of infec tion to develop. This is why avian influenza, especially the influenza of waterfowl, has great importance both in historic perspective and a t the present time.