Molecular diagnosis of infectious bursal disease outbreak in chickens in and around Aizawl district of Mizoram, India

A study was conducted during the period from April, 2020 to March, 2021 to survey the occurrence of infectious bursal disease, as well as to study the pathology and its diagnosis in chickens in and around Aizawl, Mizoram. A total of 358 dead birds were collected from different organized and unorganized poultry farms in and around Aizawl, Mizoram. IBD was presumptively diagnosed in 62 (17.31%) cases basing on history, clinical signs, gross and histopathology. Most of the cases were seen in the age group of 3-6 weeks with morbidity, mortality and case fatality rates of 39.17-47.25%, 16.11-23.73% and 39.19-50.22%, respectively. The disease was found to occur throughout the entire year with more incidences during winter season followed by summer and rainy seasons. Typical signs exhibited by the affected flocks were acute onset of depression, dullness, dehydration, anorexia, slight tremors during the onset of disease, closed eyes, droopy appearance and ruffed feathers along with whitish loose or mucoid diarrhoea. Most of the affected birds were having tendency for vent pecking, soiled vent feathers and inflammation of cloacae. On necropsy, carcasses showed dark discoloration of thigh and pectoral musculature with paint brush hemorrhages. Bursa were swollen, congested, edematous with accumulation of thick mucoid exudates; while in some cases there were presence of caseative mass inside bursa and hemorrhages were recorded at the junction of proventriculus and gizzard. Microscopic examination of bursa revealed complete lymphoid depletion leading to formation of cysts filled with heterophils and exudates and extensive hemorrhages in interfolicular tissue. Out of 62 (17.31%) chickens clinically suspected for IBD, 37 cases (59.67%) were confirmed by RT-PCR.