Factors involved in the pathogenesis of fowl typhoid

Abstract

Salmonella enterica subsp. enterica serovar Gallinarum biovar Gallinarum (SG) is the etiologic agent of fowl typhoid, a severe disease that occurs in birds of any age. Salmonella enterica subsp. enterica serovar Gallinarum biovar Pullorum (SP) is the pathogen responsible for pullorum disease, a severe systemic illness which occurs mainly in chicks, induces a carrier state in some of them and may be vertically transmitted to the progeny. Both pathogens are genetically and phenotypically similar but showing distinct pathogenicity and epidemiology. It is believed that SP has genetic mechanisms which allow it to distinctively modulate the host immune response. Comparing the whole genomes of these bacteria, it was not possible to identify any structural changes in virulence genes but only in those linked to metabolism. Therefore, it is possible that there is differential regulation of virulence genes stemming from their distinct metabolic capabilities. For evaluation of factors involved in fowl typhoid pathogenesis, two studies will be performed. The first study, involves the construction of SG mutant strains and evaluation of the mortality and carrier state in 5-day-old birds infected orally. Additionally, the immune response will be assessed in the spleen and cecal tonsils during infection. The second experiment, will evaluate the avian innate immunity against SG infection in two different lineages of layer-hens. White layers (light lineage) and semi-heavy layers will be infected and the influx of ³´ T lymphocytes will be evaluated by immunohistochemistry in liver and caecal tonsils and by qRT-PCR for quantification of pro-inflammatory cytokines in these organs. (AU)