Histopathologic and mycologic aspects of experimental infection of guinea pigs with Microsporum canis

Braz. J. vet. Res. anim. Sci., São Paulo, v. 39, n. 5, p. 238-243, 2002. Histopathologic and mycologic aspects of experimental infection of guinea pigs with Microsporum canis Aspectos histopatológicos e micológicos da infecção experimental de cobaias com Microsporum canis Josemara Neves CAVALCANTI1 ; José Luiz GUERRA2; Walderez GAMBALE3; Benedito CORRÊA3; Claudete Rodrigues PAULA3 CORRESPONDENCE TO: JOSEMARA NEVES CAVALCANTI Faculdade de Medicina Veterinária Centro Regional da Universidade de Espírito Santo do Pinhal Av. Helio Vergueiro Leite, 01 - Caixa Postal 5 13990-000 - Espírito Santo do Pinhal - SP e-mail: 1- Faculdade de Medicina Veterinária do Centro Regional da Universidade de Espírito Santo do Pinhal, Espírito Santo do Pinhal - SP 2- Departamento de Patologia da Faculdade de Medicina Veterinária e Zootecnia da USP, São Paulo - SP 3- Departamento de Microbiologia do Instituto de Ciências Biológicas da USP, São Paulo - SP SUMMARY Dermatophytosis is a zoonosis in whose etiology the dermatophyte Microsporum canis is frequently involved. The fungus can be transmitted to man by dogs and cats. In the present study, guinea pigs were experimentally inoculated with M. canis and the course of the lesions was evaluated. Inoculation resulted in lesions in 100% of the animals, with a clinical course consisting of an incubation period, an inflammatory and a phase of lesion resolution. The histopathologic evaluation of the skin biopsies revealed the presence of acanthosis, hyperkeratosis, spongiosis and marked dermal edema. M. canis spores and hyphae were detected in histologic sections stained with periodic acidSchiff. The combination of the fluorescent dyes FD and EB permitted the adequate visualization of viable and dead fungal cells in skin fragments of guinea pigs inoculated with M. canis and the identification of the morphologic characteristics of the cells. This experimental model represents a valuable instrument for the study of the pathogenesis of dermatophytic infection with respect to the evaluation of the efficacy of antifungal drugs, and may also be used for the study of the immunology of dermatophytoses and of dermatophyte morphogenes KEY-WORDS: Dermatophytosis. Microsporum canis. Ringworm. Guinea pigs. INTRODUCTION D ermatophytosis, also called tinea, ringworm, or superficial fungal infection, is one of the most common diseases of the skin and is caused by dermatophytes of the genera Microsporum, Trichophyton and Epidermophyton, which show great affinity for the skin and its annexes 5,16 . In Brazil, the most frequently diagnosed agents in the clinical dermatology of dogs and cats are in decreasing order of occurrence Microsporum canis, M. gypseum, Trichophyton mentagrophytes and T. verrucosum12, 14, 27, 39. Dermatophytosis, especially feline dermatophytosis, is an important public health problem, since M. canis is a dermatophyte that frequently infects humans, with transmission of the infestation to humans being observed in 30% of feline dermatophytosis cases13,31. According to Quaife and Womar37 and Gambale et 15 al. , dogs and cats without clinical manifestations of the disease can carry dermatophytes in their coat. Mantovani29 showed that, in addition to dogs and cats, numerous other animals, including wild animals, can harbor dermatophytes 238 and transmit the disease to man and other animals. Dermatophytes can be transmitted by direct contact with the infected host through fomites containing infected material, or by exposure to environments contaminated with spores from coats or from cells shed from the skin 30. Young animals and older animals with immunological deficiency or debilitating disease are among those most susceptible to dermatophytosis. Corticoid treatment, stress and nutritional deficiencies are also factors that may predispose to the disease16, 38. No sex or race preference has been observed, although some individuals of a family or race have been found to be more susceptible to the disease22. The classical dermatophytic lesions are characterized by policyclic, nummular rings. Alopecia and crusts can be observed. The hairs remaining in the central area or borders of the lesion are fine and brittle. Secondary papular folliculitis and dry seborrhea may also be present. Normally, pruritus does not occur, but moderate or intense pruritic lesions have been observed in some cases6,16. The diagnosis of dermatophytosis is based on clinical history, detection of lesions, and various diagnostic tests including Wood’s light interposition, direct microscopic CAVALCANTI, J.N.; GUERRA, J.L.; GAMBALE, W.; CORRÊA, B.; PAULA, C.R. Aspectos histopatológicos e micológicos da infecção experimental de cobaias com Microsporum canis. Braz. J. vet. Res. anim. Sci., São Paulo, v.39, n.5, p. 238-243, 2002. examination of the hairs and/or crusts, mycologic cultivation of perilesional material, and biopsy16,30. Despite the large number of diagnostic methods available, none of them is completely efficient38. Microscopically, the dermatophytic lesions show variable patterns, ranging from a noninflammatory to discrete reaction in association with spores or hyphae in the stratum corneum or in the hair follicles, to an intense inflammatory reaction without evidence of fungal elements. Fungal particles can be visualized in histologic sections by special staining methods such as silver methenamine or periodic acid-Schiff (PAS)22. Gross et al.16 observed dermatophytosis with variable degrees of acanthosis of the epidermis and follicular infundibulum, hyperkeratosis and, in some cases, superficial crusts. Folliculitis may be observed in dogs but does not occur in cats. The hair follicles and blood vessels of the superficial dermis are found to be infiltrated by lymphocytes and macrophages and, sometimes, by few neutrophils. The hairs can be infiltrated by dermatophytic spores and hyphae. The combined use of fluorescein diacetate and ethidium bromide (FD-EB) has been widely employed in studies on microorganism viability8, 10, 20, 28, 35, 36 using clinical material obtained from natural human and animal lesions and from experimental inoculations, that was proceeded by the standardization of the fluorescent FD-EB technique for the study of fungal cell viability. region of the animals was removed and a skin area in this region of approximately 4 cm was submitted to gentle scarification with a sterile scalpel blade. A suspension (0.4 ml) containing 106 M. canis spores/ml was inoculated at the site, which was covered with a 4 x 4 cm polyethylene film and kept in place with a 4-cm high elastic bandage for 24 h. Preparation and quantification the inoculum The suspensions used for the inoculation were prepared from M. canis colonies initially cultivated on Mycosel (DIFCO) and then on potato agar for approximately 2 to 3 weeks at 25oC. The colonies were gently scraped from the surface of the culture medium, placed in test tubes containing 20 ml sterile saline, and triturate (...truncated)