[Long term surveys on Tyzzer's disease in three rat breeder colonies (author's transl)]

Retired rats of SD strain from three breeder colonies (A, B and C) were monthly monitored for CF antibody to Tyzzer's organism for 2 to 6 years. In colony A, antibody-positive rats were found at frequencies ranging from 5 tp 100% with a single peak during about one year without any detectable signs of apparent disease. However, in colony B, in spite of the outbreak of the disease, antibody-positive animals were only sporadically detected during about 4 years after the outbreak. Thereafter, in this colony, the antibody was not demonstrated in all animals examined for 2 years, and susceptibility to the disease of 3-week-old rats was the same as that of ones from one-infected colony. Cortisone test did not suggest the infection. In colony C, no antibody-positive rats were detected for 3 years.