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An epizootic of necrotic dermatitis in laboratory mice caused by Lancefield group G streptococci
Abstract:
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.
Insights
A streptococcus infection caused severe necrotic dermatitis and paralysis in mice during a toxicology study. Bites from infected mice likely spread the bacteria, leading to significant mortality.
Area of Science:
- Veterinary Pathology
- Microbiology
- Toxicology
Background:
- Mice in a toxicology experiment exhibited severe progressive necrotic dermatitis and paralysis.
- A high mortality rate of 35% (134/383) was observed in the affected mouse group over seven months.
Purpose of the Study:
- To identify the causative agent of the observed necrotic dermatitis and paralysis in mice.
- To investigate the role of a specific bacterium in the disease outbreak.
Main Methods:
- Bacteriological and histopathological examinations were performed on seventeen necropsied mice.
- Cultures were taken from skin lesions, throats, spleens, and other sites.
- Experimental inoculation of isolated bacteria was used to reproduce skin lesions.
Main Results:
- A Lancefield group G streptococcus was consistently isolated from skin lesions, throats, and spleens of affected mice.
- Histopathology revealed necrotic dermatitis with epithelial ulceration and suppuration.
- Inoculation of the isolated streptococcus successfully reproduced skin lesions in 6 out of 15 mice.
Conclusions:
- Lancefield group G streptococcus was identified as the causative agent of the necrotic dermatitis and paralysis in the mouse colony.
- The study suggests that bites from infected mice, carrying the streptococcus in their oral flora, initiated and perpetuated the outbreak.
- The findings highlight the potential for bacterial infections to complicate toxicology studies and impact animal welfare.
