Concurrent outbreak of staphylococcal pneumonia with infectious bursal disease in broiler chickens

Concurrent outbreak of staphylococcal pneumonia with infectious bursal disease (IBD) occurred in 29-day-old broiler chickens. The outbreak started after a flock of 279 birds was decongested by moving 121 birds to another pen. The birds were depressed and weak before death and carcasses were cyanotic. At necropsy, the lungs were dark red, congested and consolidated; the bursa of Fabricius (BF) was enlarged; the liver was pale and the intestinal mucosa was hyperaemic. Histopathological examination of the lungs, BF and liver revealed fibrinopurulent pneumonia, purulent inflammation of the BF and hepatic lipidosis, respectively. Staphylococcus aureus was isolated from the teased tissue of the lungs. The mortality was 35.8% within 5 days of the outbreak. The circumstances of the outbreak suggested that immunosuppression due to stress associated with crowding and transferring of the birds from one pen to another and poor seroconversion to previous infectious bursal disease virus vaccination, favoured the clinical establishment of the bacterial and IBD viral infections.