HISTOPATHOLOGICAL AND MOLECULAR DETECTION OF SALMONELLOSIS IN POULTRY IN CHITTAGONG

Abstract

Salmonellosis is one of the most important bacterial diseases of poultry because it causes high economic loss due to mortality and reduced egg production in layer birds. Salmonella infection in poultry can occur in either acute or chronic form by the member of genus Salmonella under Enterobacteriaceae family. There are mainly two biovars of avian species (host) specific Salmonella enterica named Salmonella Gallinarum and Salmonella Pullorum which are responsible for fowl typhoid and pullorum disease respectively. The present study was undertaken with the aim to carry out pathological and molecular identification of Salmonella isolated from commercial chickens in Chittagong. For this purpose a cross sectional survey was done with the collection of 90 different samples from dead chickens (38 Layers, 37 Broilers and 15 Sonali) brought to the department of Pathology and Parasitology, Chittagong Veterinary and Animal Sciences University (CVASU) for postmortem examination. A preformed questionnaire was also used to record additional information such as production type, farm size, vaccination etc. All the postmortem samples were primarily inoculated into selenite cystine broth followed by streaking into XLD agar to determine typical colony characteristics of Salmonella. Out of 90 samples 16 (17.78%, 95% CI 10.5-27.3%) were found primarily positive on XLD agar based on colony morphology which was also tested by Polymerase Chain Reaction (PCR) using previously published primer to detect invA gene specific for Salmonella. After PCR, 13(14.44%) samples were found positive (95% CI 7.9-23.4%) with the amplicon size of 284bp in agarose gel electrophoresis. Additionally liver, lung, spleen, kidney and intestine were also collected and preserved in 10% buffered formalin for histopathological examination. Gross pathological changes observed during necropsy included misshapened ova, unabsorbed yolk sac in chicks, bronze colored liver, haemorrhages and necrotic foci in spleen and intestine. Histopathological investigation showed congestion and hemorrhages in lungs; coagulation necrosis and fatty change in liver; congestion and haemorrhage in kidney which was also associated with coagulation necrosis and fatty change in renal tubule in some cases. Marked destruction of intestinal epithelia with caseous mass in intestinal lumen was found along with haemorrhage and sloughed off villi. Depletion of lymphocytic nodule and lymphocytes along with vascular thickening in spleen was markedly observed in most of the cases. Necrosis, proliferation of Reticuloendothelial (RE) cells and presence of secondary follicles were also noticeable lesions in spleen. Univariable logistic regression was used to identify the effect of different variables on the estimated prevalence (14.44%) of Salmonella. Statistically significant difference (p<0.05) was observed in the prevalence of salmonellosis in different production type of chickens. Prevalence in layer (26%, OR=4) was significantly higher compared to broiler (8%, OR=1). The result of the present study indicates the importance of PCR as a rapid and reliable tool alongside conventional cultural techniques for screening Salmonella. The data of risk factor analysis in this study suggest the prevalence of Salmonella enterica is very high in commercial layers in Chittagong.