SUMMARY
Salmonellosis is a critical challenge in commercial poultry farming. This study aimed to calculate seroprevalence, identify Salmonella spp., and its pathological investigation from January to December 2019. One hundred fifty (150) serum samples and fifty (50) cloacal swabs from apparently ill and healthy birds were collected in this study. Seroprevalence was observed by serum plate agglutination (SPA) tests. The tentative diagnosis of salmonellosis was made based on history, clinical signs and bacteriological studies. Salmonella spp. was further confirmed using an automated microbiological method (VITEK®2). Post mortem examination was done in apparently sick birds, and gross and microscopic pathological lesions were investigated and recorded in a datasheet. The overall seroprevalence of salmonellosis was 42.67% in commercial chickens. Age wise prevalence of avian salmonellosis showed significantly highest infection rate in adult layers (= 45 days old) 65.31%, then 40.74%up to 45 days. In case of broiler, the prevalence rate in 0-10 days, 11-20 days, and 21-35 days were 13.63%, 44.12%, and 16.67%, respectively. Seasonal influence showed significantly highest proportionate prevalence of salmonellosis during summer 66.15%in comparison to winter 25.00% and rainy 24.44% seasons respectively. In bacteriological study, 12 samples were positive for Salmonellae among 50 cloacal samples. Out of 12 positive samples 5 samples were selected for the automated microbiology system VITEK® 2, and only two samples were confirmed as Salmonella gallinarum. Gross pathology of representative organs revealed bronze-colored enlarged liver, hemorrhages in the spleen and lungs, and hemorrhages in the ovary with stalk development. Microscopically, multifocal nodule formation and infiltration of inflammatory cells in the liver parenchyma and marked congestion with inflammatory cells in the spleen, hemorrhage and congestion in the lungs and intestine.