Role of parrots in the epizootiology of newcastle disease

Abstract

The incidence, susceptibility, mode of infection and duration of excretion of the new cattle disease virus in the common Indian parrots (psittacula Krameri) were studied in detail. The blood, cloacal and throat swabs of parrots, collected from different parts of the State were screened for the presence of ND antibodies and virus. Seventeen out of 103 blood samples were found to possess HI antibodies. The serum samples which gave positive HI titres belonged to parrots kept as pets in households and allowed to mingle freely with domestic poultry and those housed in Trivandrum Zoo along with pigeons. None of the 70 cloacal and 42 throat swabs were positive for the virus.

Experimental infection of parrots with undiluted virulent virus by the intranasal and intraocular routes and by the subcutaneous and intranasal routes with 1:100 dilution of the same virus gave almost the same results. All of them died within a weeks’ time, after showing symptoms of inappettance, leg and wing paralysis and diarrhoea, from day two of infection. Virus could be isolated from the throat and cloacal swabs and also from the tissue of dead birds.

Chicks kept along with these infected parrots did not develop symptoms of ND, eventhough they excreted the virus, for a few days, and had a low titre of HI antibodies in their sera. All the contact chicks died of ND with typical symptoms and lesions on challenge with the virulent virus. The parrots that received a mesogenic strain (Komorov) of the virus, also succumbed to the disease, but with less pronounced symptoms and with an extended incubation period.

The parrots that were infected with lentogenic strain of the virus (F1) did not develop symptoms of the disease. However multiplication of the virus occurred in these birds as isolations could be made from cloacal and throat swab and a slight increase in H1 titre was noticed sera. However on challenge with a virulent strain of NDV, they showed symptoms of ND. All of them died within eight days and the virus could be isolated from them.

Contact infection of parrots from infected chicks were quite effective, as the parrots died with the same symptoms described above, almost within the same time as direct infection. Virus was also isolated from the tissues of the dead parrots.

The common Indian parrots were found to be highly susceptible to both velogenic and mesogenic strains of NDV, but they were resistant to the lentogenic strain. Uninfected chicks kept along with the parrots infected with virulent virus picked up the infection, and virus could be isolated from the cloacal and throat swabs of these chicks. They also showed an increase in the antibody titre. The failure to produce clinical disease in chicken might be attributed to a decrease in virulence of the virus on passage in parrots. The carrier state with the lentogenis strain of the virus could not be assessed as they were challenged after 2 weeks.

Though a carrier role had been attributed to the parakeets imported from India, the parrots in this study were found to succumb to the disease within a week. This might be due to the variation in the susceptibility of various species of parrots to NDV. The chances of dissemination of the virus could be prevented by quarantining them for a period, not less than ten days.