Susceptibility of ducks to newcastle disease virus (NDV) and their role in the transmission of the disease to chicken

Abstract

The susceptibility of ducks to Newcastle disease virus and their possible role in the epizootiology of this disease were investigated. Cloacal and throat swabs and sera were collected from clinically normal as well as diseased ducks from different parts of Kerala. The swabs were tested for virus excertion by inoculating into the allantoic cavity of 10 day embryonated chicken eggs and the sera were examined for the presence of haemagglutination inhibition antibodies. Eight and one week – old ducklings were infected experimentally by different routes or methods to find out their susceptibility to this virus. A virulent strain of the virus received from Veterinary Biological Institute, Palode was employed for all experimental infection studies. Two week – old chickens were used for determining contact transmission. Inoculation of processed cloacal and throat swabs into the allantoic cavity of 10 day embryonated eggs resulted in the isolation of eleven haemagglutinating viruses from a total of 151 samples. The agglutination produced by these viruses were inhibited by specific ND antiserum, thereby confirming their identity as Newcastle disease virus. Out of a total of 226 serum samples collected from ducks, 34 showed HI antibodies ranging from 1:20 to 1:160 in the titre. Eight week – old ducklings infected intranasally and intraocularly showed symptoms of ND by third day of infection but recovered by the seventh day. All of them excreted the virus either through trachea, cloaca or by both the routes. Haemagglutination inhibition antibodies were demonstrable within two weeks of infection. The chickens kept in contact with the infected ducklings died after showing specific symptoms of newcastle disease. Postmortem examination revealed specific lesions and virus could be isolated from pooled tissue samples. Week – old ducklings could successfully be infected by intranasal/intraocular, subcutaneous, intramuscular or by contact infection. All the ducklings exposed to infection died after showing symptoms of pneumoencephalitis and diarrhoea. Virus was isolated from seventeen out of twenty five cases. Chickens placed in contact with subcutaneously infected ducklings died showing specific symptoms and lesions in ND and virus could be isolated from all the cases. The eight week – old ducklings although showed a clinical infection they could eventually recover following the development of antibodies in the system. Hence ducklings of eight weeks and above could be considered as resistant to newcastle disease virus infection. On the contrary week – old ducklings readily succumbed to the infection indicating their grater susceptibility. Contact transmission to chickens was possible from both age group of ducklings. The isolation of virus from clinically normal and diseased ducks showed that ducks excrete the virus without showing any clinical symptoms. It is also possible that some ducklings may show symptoms of the disease, but the development of antibody in the system leads to complete elimination of the virus. The results and the observation of the present study indicate that ducks can play an important role in the epizootiology of Newcastle disease by contracting infection from infected chicken or from other susceptible species and transmitting it to the incontact susceptible chicken.