An outbreak of Trichophyton mentagrophytes infection in a rat breeding stock and its successful control

Abstract

An outbreak of dermatophytosis by Trichophyton mentagrophytes infection was observed in a breeding stock of the Wistar-Imamichi rat. Typical cutaneous lesions such as alopecia and hyperkeratosis due to the fungus were observed in 10% and 44% of adult females, and males respectively. No infection was seen in infant, even in those fostered by infected females. By 3 repeated cultivations of the hair, T. mentagrophytes was isolated from 107 (90.7%) of 118 rats clinically diagnosed as dermatophytosis. In order to maintain the original stock, the usual wholesale slaughter program was avoided and the following control measures were taken. After sacrificing all rats with the cutaneous lesions, the breeding colony was transferred temporarily to a separate animal room. The resulting vacant room was then disinfected 3 times with 10% formalin, followed by spraying with 3% sodium propionate solution 3 month later. The progenies from the non-infected mothers were dipped into 3% sodium propionate solution and transferred back into the disinfected animal room for re-colonization. Frequent sterilization of all equipment with iodophor, balsam and formalin was carried out. The room sterilized monthly with iodophor and 70% alcohol. Daily observation of all rats and monthly screening by culture test was done thereafter. As a result, no infection has been detected 4 month after recolonization, except for the 3 rats which were sacrificed immediately after detection. On the basis of the culture test and clinical observation, no infection was observed in the treated rat colony for the next five following years. Therefore, the effectiveness of these procedures of the eradication of T. mentagrophytes infection from a rat colony was shown to be quite reliable.