Ecology of Ringworm Fungi on Commensal Rats from Rural Premises in Southwestern Georgia

Abstract

Summary Two of the fungi, Trichophyton mentagrophytes and Microsporum gypseum which cause ringworm in man infect many domestic and wild animals in nature. Most of the human cases of T. mentagrophytes in rural areas are presumed to be of animal origin, but M. gypseum infections are believed to be acquired more often from soil contacts. Commensal rats were collected from rural premises in four counties of south-western Georgia and their hairs were tested for ringworm. Approximately 5 per cent of the 350 Norway rats and 7 per cent of the 84 roof rats trapped had ring-worm infections as shown by culture methods. Only Norway rats were caught in Mitchell County and none of 150 specimens were found infected. Rats positive to T. mentagrophytes came only from Grady and Thomas Counties. Two Norway rats from the 35 trapped in Baker County showed the presence of M. gypseum. The degree of rat infestation of premises as indicated by success in trapping was directly related to the percentages of premises with ringworm-positive rats. An inverse relationship between the degrees of rat infestation of premises and percentages of rats infected by ringworm was indicated by the limited data considered. Twenty-eight soil samples taken from rat ranges on six premises where ring-worm-positive rats were trapped showed the presence of M. gypseum only, over half of the samples containing this primarily saprophytic fungus.