Further investigations on the epidemiology of fowl typhoid in Brazil

Abstract

Salmonella Gallinarum (SG) causes fowl typhoid (FT), a disease responsible for economic losses to the poultry industry worldwide. FT has been considered to be under control in Brazil; nevertheless, since 2012 it has frequently been identified in poultry farming of several Brazilian states. The present study was aimed at assessing (i) the pathogenicity of a SG strain recently isolated from an FT outbreak affecting chickens of both white and brown layers; (ii) the transmission of SG through eggs and hatching; (iii) the effects of antibiotic therapy on SG persistence in poultry tissues and on its vertical transmission and (iv) the genetic profiles of strains isolated over 27 years by Pulsed Field Gel Electrophoresis. Clinical signs, mortality and gross pathologies were very marked amongst brown-egg layers. In contrast, clinical manifestation of FT and mortality were barely present amongst the white-egg layers, although bacteria could be re-isolated from their tissues up to 35 days after infection. No bacteria were re-isolated from the laid eggs, so vertical transmission was not achieved, although newly hatched uninfected chicks became infected spontaneously after hatching. Antibiotic therapy was shown to be effective at reducing mortality, but was not able to clear infection or to favour SG transmission via eggs. Our pulsed field gel electrophoresis results revealed an endemic SG clone that may have been circulating in the Brazilian poultry flocks in the south and southeast regions for more than 20 years. The results suggest that the industrial incubation of SG-contaminated eggs could be one of the factors responsible for the spread of FT in Brazil.