A < em > Salmonella < /em > Pullorum outbreak with neurological signs in adult layers and outbreak investigation using Whole Genome Sequencing

This report describes a Salmonella enterica subspecies enterica serovar Gallinarum biovar Pullorum (SP) outbreak in a Dutch laying flock of 65 weeks of age (W) showing increased mortality, decreased egg production and neurological signs. The flock was vaccinated three times with a live S. Enteritis and S. Typhimurium vaccine in the rearing period. At 71 W, as mortality peaked, a live SG 9R vaccine was applied. At 76 W mortality decreased and egg production stabilized but did not return to a normal level.Post-mortem, histological, bacteriological and serological examinations were frequently performed. Gross findings in diseased and dead birds were characterized by hepato- and splenomegaly and oophoritis. SP was frequently isolated from liver, spleen, ovary and bone marrow and isolation rate did not vary significantly between the different organs. Histological examination and immunostaining of birds with neurological signs showed cerebral granulomas in the presence of Salmonella. Previous Salmonella vaccinations did not hamper the detection of specific SP antibodies (positive at serum dilution ≥ 1:8) using a commercial rapid plate agglutination test. At 85 W 40 clinically healthy birds were investigated and three had ovarian lesions, explaining egg production not returning to normal. These birds had antibodies against SP, indicating contact with the bacterium, but carrier status could not be confirmed by culture. phylogenetic analysis showed SP isolates within this outbreak t...
Source: Avian Pathology - Category: Pathology Authors: Source Type: research