Experimental Infection of Turkeys with A Virulent Newcastle Disease Virus Isolated from Broiler Chickens

Newcastle disease (ND) is a highly contagious infection of many avian species, mainly chickens and turkeys, with a devastating impact on worldwide poultry production. The ND accounts for heavy losses in Iranian poultry flocks. There are some reports regarding the epidemiology of this infection in Iran. This study was performed to investigate the infection of turkeys with a Newcastle disease virus (NDV) isolated from a broiler chicken flock in southwestern Iran during 2013. For the purpose of the study, 70 day-old Wishard bronze poults were allocated into two groups of control (n=25) and infected (n=45). At 32 days of age, each bird in the infected group was inoculated with 0.1 mL (50 μL per eye) of NDV-infected allantoic fluid through an ocular route and received 105 EID50 of viral inoculum. On the other hand, the birds in the control group were inoculated with phosphate buffered saline by the same route. Swab samples were taken from both groups at different time points, namely from 1 to 21 days postinoculation, and verified for NDV infection by using reverse transcription-polymerase chain reaction (RT-PCR). Both groups were also examined serologically by haemagglutination inhibition test. Clinically, the infected turkeys exhibited anorexia, severe depression, sitting on the hock joint, white to greenish (sometimes bloody) diarrhea, neurological disorders, and mild respiratory problems. Out of 45 inoculated birds, 9 (20%) cases died. Based on RT-PCR, virus shedding was observed in the challenged birds 3-8 days postinoculation. The NDV was detected more in tracheal swabs (50%) than in cloacal swabs (12.5%). The infected birds showed a high seroconversion. Therefore, the NDV circulating in Iranian chicken flocks has the potential to cause a serious illness in commercial turkeys. The vaccination of turkeys, as well as biosecurity, should be considered carefully to prevent the ND outbreaks in the future.