Newcastle disease--seroepidemiologic study of a highly contagious epizootic in poultry and in wild birds in Switzerland

Newcastle disease (ND) is a highly contagious viral disease particularly of domestic poultry. Switzerland is currently declared free from ND. A serosurvey using an ELISA was performed to investigate infections with ND-Virus (NDV) in 260 Swiss laying hen flocks, 169 backyard poultry flocks and 1576 wild birds. For laying hen flocks, a stochastic model was applied to analyse the results from serological testing. Four laying hen flocks were identified as NDV-seropositive, and the true NDV seroprevalence in this population was most likely between 1.3 and 1.5%. NDV antibodies were also detected in five of the 169 backyard poultry-flocks. ND-antibody positive birds were found in 10% of all wild birds examined, with the highest proportions among cormorants, grebes, birds of prey, owls, and swifts. The study indicated that positive flocks must have been in contact with NDV strains causing sub-clinical infection, since no clinical signs had been observed. Moreover, trade of poultry or poultry eggs was considered to be an important factor associated with seropositivity in backyard poultry flocks. Contact to wild birds did not seem to be of major importance.