Viral respiratory diseases complex: Investigation on the relevance of Newcastle disease virus in vaccinated poultry flocks in Egypt and characterization of further detected viruses

Newcastle disease (ND) is. Because of the endemic ND situation in Egypt with expected high economic losses, intensivevaccination programs are in widely applied. For broilers, vaccination programs during the 35- 40 days of the fattening period includes at least two applications of live vaccines, often with one an inactivated vaccine in between. For layers and breeders, an intensive vaccination scheme used during rearing the chicks with repeated application of live and inactivated vaccines that may be followed by another vaccinations during the production period according to the need. Nevertheless, continuous ND outbreaks are reported and linked to high losses especially in broiler farms. Detection of NDV in these farms are considered as indication for failure of vaccination and hygienic measures. This discussion is inspired by an observed phylogenetic distance between of vaccine type virus strains, that were established in the late 1940ies and current viruses associated to ongoing outbreaks. Even though, recent studies show to a great extent clinical protection from disease by established vaccines, regardless of the genotype. In this context, it is important to note, that diagnosis of ND relies mostly on the clinical signs in conjunction with post mortem findings. However, virus detection is restricted to generic detection of NDV without differentiating the pathotype. In consequence, clinical suspicion for ND outbreaks in vaccinated farms might be superimposed or caused by other pathogens and detected NDV is the vaccine type virus. The current study attempted to investigate the prevalence / relevance of virulent NDV in flocks that suffer from respiratory distress accompanied with elevated mortality in Egypt. Beside detection of NDV, relevant viral infections, i.e. IBV and Avian Influenza virus (AIV) should be included in the deferential diagnostic approach. The detected viruses should be used to determine the circulating virus strains and to investigate potential antigenic mismatch of obtained NDV field isolates. Appropriate monoclonal mouse antibodies should be established to further depict possible genotype specific antigenic sites of NDV. These results are mandatory to study potential antigenic drift of prevalent NDV in Egypt and should help to translate sequence information into information of the antigenic properties of NDV.