Epidemiological studies of Bacillus piliformis infection and Tyzzer's disease in laboratory rats

Characteristics in connection with the presence of Bacillus piliformis in the barrier-protected animal rooms of a breeding centre for laboratory rats are discussed. The incidence of antibodies against B. piliformis in IFA test is high -77.8% for the total breeding centre. Clinical and pathological changes are, however, rare and mainly connected with certain rat strains. Immunosuppression with prednisolone and subsequent histopathological tests of liver sections indicate that rats with MHC-type RT1.A-u have an increased risk of developing Tyzzer's disease, while RT1.A-1-carriers seem to be resistant to this disease.