An epizootic of necrotic dermatitis in laboratory mice caused by Lancefield group G streptococci.

During a 7-mo period, mice from a group of 383 being used in a toxicology experiment developed severe progressive necrotic dermatitis, and some animals developed paralysis. The overall mortality rate for the group was 134/383 (35%). Seventeen mice were necropsied for bacteriologic and histopathologic examination. A streptococcus identified as Lancefield group G was isolated from the skin lesions of 15 of the mice, from 8 of 9 throats cultured, from 4 of 8 spleens, and occasionally from other sites. It was thought that the infections were initiated and perpetuated by bites from mice carrying the streptococcus in their mouth and throats. Microscopic examination of affected skin revealed necrotic dermatitis characterized by epithelial ulceration with suppuration. The skin lesions were reproduced in 6 of 15 mice inoculated with the isolated streptococcus.