To date, highly pathogenic avian influenza virus type A of subtype H5N1 [HPAI A(H5N1)] has been detected in wild birds in 24 European countries. Germany had the highest incidence in Europe in 20067 2007 with more than 670 wild birds and 1 zoo bird testing HPAI A(H5Nl)-positive. From February 2006 through September 2006,344 wild birds of approximately 70,000 animals tested were positive. During 2007, 326 wild birds infected with HPAI A(H5N1) viruses (of approximately 20,000 tested) were found in various parts of Germany. Additionally, in 2006,1 poultry farm and 1 zoo animal (black swan) in Saxony were found to be HPAI A(H5Nl)-positive. Governmental regulations were implemented immediately in order to prevent infection of other birds, mammals, and humans. Susceptibility to the virus varies greatly among bird species. Among wild birds, waterfowl, and raptors seem to be affected the most, followed by corvids and other birds that include carrion in their diet. Wild passerine birds were not found HPAI A(H5N1) positive. Inoculation experiments with HPAI A(H5N1) on pigeons showed this species to be only slightly susceptible. Clinical and pathological findings were also species-specific: pigeons primarily exhibited CNS symptoms and necropsy revealed a lymphohistiocytic meningoencaphalitis, whereas in wild birds and raptors, the virus exhibited higher viscerotropism, causing hepatitis, splenitis, enteritis, nephritis, inflammation of the entire respiratory tract, and, as the main finding in waterfowl, acute pancreatitis. Immunization of farm poultry is unfeasible and, to date, there is no H5Nl-specific vaccine on the market. However, other commercially available Influenza A vaccines have been used to promote immunity in zoo birds, and their efficacy to protect from clinical disease, as tested on raptors, has been high.
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