zoonoses and communicable diseases common to ... - PAHO/WHO

336 MYCOSESsible to determine how the infection had been introduced, but its spread throughoutthe establishment was undoubtedly due to shearing implements and close contactamong the animals immediately after being sheared (Jackson et al., 1991).SWINE: The most common agent of swine tinea is M. nanum. Infection has beenconfirmed in Australia, Canada, Cuba, Kenya, Mexico, New Guinea, New Zealand,and the United States. This dermatophyte was isolated in only a few human cases.The lesion is characterized by a wrinkled area covered by a thin, brown scab thatdetaches easily. M. nanum lives as a soil saprophyte in areas where swine are raisedand is classified as geophilic.FOWL: Tinea favus in hens occurs sporadically throughout the world and is rarelytransmitted to man. Its agent is T. gallinae.Source of Infection and Mode of Transmission: The natural reservoirs ofzoophilic dermatophytes are animals. Transmission to man occurs through contactwith an infected animal (either sick or a carrier) or indirectly through spores containedin the hair and dermal scales shed by the animal. Dermatophytes remain viablein shed epithelium for several months or even years. The same animal can infect severalpeople within a family, but a zoophilic dermatophyte does not usually spreadfrom person to person and, unlike the anthropophilic dermatophytes, does not causeepidemic tinea. Cases of human-to-human transmission of M. canis have beenobserved, but the agent loses its infectiveness for man after a few intermediaries(Padhye, 1980). A nosocomial infection was described in a nursery for newborns.Although tinea of the scalp is common among children, it is rarely found in newborns.The common source of the infection turned out to be a nurse who had an indolentinfection due to M. canis (Snider et al., 1993). T. verrucosum, whose principalreservoir is cattle, is found in infections in rural populations. A study conducted inSwitzerland found that 14% of those working with infected cattle contracted dermatophytosiscaused by T. verrucosum (Haub, as reported to Gudding et al., 1991).This mycosis also has economic consequences, in that skins from the infected animaldepreciate in value. It is a reportable disease in Norway. In contrast, M. canis is transmittedby cats and dogs to urban and rural populations. The cat is considered the principalsource of infection for humans due to the custom of picking up and petting acat, as well as to its high rate of infection. Cats can also host the anthropophilic dermatophyte,T. rubrum, in their hair, but it has not been demonstrated that they cantransmit it to man. Infection due to T. mentagrophytes var. mentagrophytes (var. granulosum)and T. mentagrophytes var. quinckeanum is indirectly transmitted fromrodents to man via residues of shed epithelium in the environment. Cats and dogs canalso become infected by these dermatophytes in the same way or by direct contactwhen they hunt rodents and can, in turn, transmit the infection to man.Animal-to-animal transmission occurs in the same ways. Crowding and reducedorganic resistance influence the incidence of infection.Role of Animals in the Epidemiology of the Disease: Animals are the reservoirof zoophilic dermatophytes and the source of infection for man. As in otherzoonoses, human-to-human transmission is rare. Transmission of anthropophilicdermatophytes from humans to animals is also rare.The dermatophyte M. gypseum is the causal agent of sporadic cases of tinea inhumans and animals; its reservoir is the soil (geophilic).