Epidemiological investigations of Salmonella and Escherichia coli associated morbidity and mortality in layer chickens in Hawassa city, Southern Ethiopia

Background: This study was conducted with the objectives of estimating the morbidity and mortality rates in layer chickens, identifying the risk factors associated with morbidity and mortality, and identifying the major bacterial pathogens affecting small-scale commercial layers in Hawassa. A longitudinal observational study design was employed from November 2019 to March 2020. The chickens on selected farms were checked for morbidity and mortality twice a week. During each visit, clinical examination of sick birds and pathological investigation of dead birds were conducted. Cloaca samples were collected for isolation and identification of Salmonella spp. and E. coli. A Cox proportional hazard model was used to quantify the effects of various risk factors on the morbidity and mortality rates observed. Results: Of the 8976 chickens followed, 106 developed clinical disease, giving a morbidity of 1.18% (95% CI: 0.97, 1.43). The overall morbidity rate was 2.37 (95% CI: 1.94, 2.87) per 1000 chicken months. A total of 101 of the chickens under study were found dead, yielding a mortality of 1.13% (95% CI: 0.92, 1.37) and a mortality rate of 2.26 (95% CI: 1.84, 2.75). Multivariable Cox regression analysis showed that farm hygiene, the experience of farm manager, housing condition, housing systems, the availability of veterinary services and age of chicken were important risk factors for morbidity and mortality. Out of 58 cloacal samples collected from sick chickens, 7 (12.07%; 95% CI: 4.99, 23.29) yielded positive results for Salmonella spp., while 25 (43.10%; 95% CI: 30.16, 56.77) yielded positive results for E. coli. Out of swabs collected from 8 randomly selected sick chickens after necropsy, 3 (37.5%) were found to be positive for Salmonella spp. Four (50%) of them were positive for E. coli. Swabs were collected and cultured from 15 dead chickens, and of these, 2 (13.33%) and 7 (46.67%) were found to be positive for Salmonella spp. and E. coli, respectively. Farm hygiene, age of chickens, housing conditions and frequency antibiotics use were important risk factors for colibacillosis and salmonellosis. Conclusions: Although the incidence of chicken morbidity and mortality was relatively low in the present study, important risk factors have been identified in the poultry farms of Hawassa City, southern Ethiopia. Therefore, comprehensive poultry farm management practices are needed to mitigate risk factors for morbidity and mortality as well as colibacillosis and salmonellosis. Identification of the serotypes of Salmonella spp. and E. coli should be carried out