Shedding of velogenic Newcastle Disease virus following experimental infection of vaccinated Pheasants

Newcastle disease (ND), together with highly pathogenic avian influenza, is one of the most devastating diseases of poultry and other birds and vaccination is one method of control. Susceptibility to Newcastle disease virus (NDV) of Phasianus colchicus is well known and during the epidemic of ND that occurred in Italy during 2000, both free-living and reared pheasants were affected. On that occasion the advisability of releasing ND vaccinated, semi-intensive reared pheasants into the wild was questioned. There was the possibility that vaccinated pheasants might develop an infection with a velogenic NDV which would then spread. In this paper an experimental infection of eight pheasants vaccinated with live and killed NDV vaccines, is reported. The birds were infected by the oronasal route with a velogenic strain of NDV which was isolated in 2000 from a wild pheasant. Birds were observed daily for clinical signs and mortality throughout the experiment. Tracheal and cloacal swabs were collected for virus isolation on tracheal organ cultures and recovery was confirmed by RT nested PCR using extracted RNA. Blood samples were collected and tested for NDV antibodies by hemagglutination-inhibition assay. Severe nervous signs were observed in one bird 6 days post infection. NDV was isolated from the trachea of 5 pheasants for varying lengths of time up to day 5 post infection. It was never recovered from the cloaca. Seroconversion was observed in all the birds. It was shown that vaccinated pheasants can become infected with a velogenic NDV and shed it by the respiratory route, though not themselves show any disease. Therefore they pose a potential threat to wild and domestic birds with which they will come into contact. This experiment highlights important health implications which may arise from management of avifauna and which should be given due consideration.