INFLUENZA-VIRUS SUBTYPES IN AQUATIC BIRDS OF EASTERN GERMANY

We report the findings of a 12-year surveillance study (1977-89) of av ian influenza A viruses in eastern Germany. Viruses were isolated dire ctly from feral ducks (n = 236) and other wild birds (n = 89); from do mestic ducks (n = 735) living on a single farm; and from white Pekin d ucks (n = 193) used as sentinels for populations of wild aquatic birds ; mainly sea birds. The efficiency of virus isolation was 9.9% overall , with considerable variability noted among species: 8.7% in wild duck s, 0.9% in other feral birds and 38% in Pekin ducks. Use of sentinel d ucks in wild pelagic bird colonies improved virus detection rates five fold, suggesting that this approach is advantageous in ecological stud ies. Among the 40 different combinations of hemagglutinin (HA) and neu raminidase (NA) subtypes we identified, H6N1 predominated (23.6% for a ll avian species), followed by H4N6 (11%). Among individual species, t he frequency profiles favored H2N3 (20.8%) and H4N6 (20.3%) in feral d ucks; H7N7 (22.3%), H4N6 (24.4%) and H2N3 (10.4%) in Pekin ducks used as sentinels; and H6N1 (34.8%) and H6N6 (15.1%) in domestic ducks main tained on a single farm. By relying on sentinel birds for serological assays, it was possible to trace an ''influenza season'' in feral swan populations, beginning in August and continuing through the winter mo nths. Comparison of subtype distribution of influenza viruses for Euro pe and North America showed significant differences. This supports the fact of two geographically distinct gene pools of influenza viruses i n birds connected with their distinct flyways of each hemisphere. The high frequency of isolation of H2 influenza viruses is of considerable interest to those interested in the recycling of this subtype in huma ns. Similarly the frequent isolation of H7N7 influenza viruses raises concern about reservoirs of potentially pathogenic influenza virus for domestic poultry. Our results confirm the existence of a vast reservo ir of influenza A viruses in European aquatic birds, which possesses s ufficient diversity to account for strains that infect lower animals a nd humans.