Dermatophytes in domestic animals

©2000 Revista Iberoamericana de Micología Apdo. 699, E-48080 Bilbao (Spain) Dermatophytes are cited among the most frequent causes of dermatological problems in domestic animals. The superficial mycoses caused by dermatophytes are called dermatophytosis, and they are commonly referred to as ringworm or tinea. In general, dermatophytes do not invade subcutaneous or deep tissues, but pseudotumoral lesions (“mycetoma”, “pseudomycetoma”) affecting the subcutaneous tissues have been described in Persian cats [1,2]. Dermatophytes are classified in three genera, Epidermophyton, Microsporum and Trichophyton, which include about 40 accepted species. However, only a few species belonging to the genera Microsporum and Trichophyton are usually the cause of dermatophytosis in domestic animals (Table 1). They are usually divided into three ecological groups according to their main natural host or habitat: the anthropophilic (humans), the zoophilic (animals) and the geophilic (soil). Only two species are included in the genus Epidermophyton. Epidermophyton floccosum is categorized as an anthropophilic species and only normally responsible for a small percentage of human dermatophytosis, although its occurrence in animals has been reported [3]. In very few cases, anthropophilic species have been mentioned as a cause of dermatophytosis in animals [3]. In very special cases, anthropophilic dermatophytes, such as T. rubrum [4], have been isolated from the coat of healthy pets. Apparently cats, which in this case [4] were living in close contact with T. rubrum infected owners, were merely carriers of viable propagules of this dermatophyte. Epidermophyton stockdaleae is categorized as a geophilic dermatophyte fungus, and so far has not been mentioned as a causal agent of dermatomycosis [5]. This species has only been isolated once before [6]. Nevertheless, most of the members of the M. gypseum complex, which are geophilic dermatophytes, are the cause of a relatively low number of cases of ringworm, both in humans and animals.On the other hand, some geophilic nonpathogenic dermatophytic species, such as M. cookei, T. ajelloi and T. terrestre, can be isolated from animal fur [7,8]. These species are included in the dermatophyte-like fungi group by some authors [9]. Animals serve as reservoirs of the zoophilic dermatophytes, and their infections have considerable zoonotic importance. Zoophilic dermatophytes such as M. canis, T.mentagrophytes var. mentagrophytes and T. verrucosum are significant causal agents of human ringworm in many areas of the world. The incidence of dermatophytosis varies according to climate and natural reservoirs. However, the pattern of the species of dermatophytes involved in dermatophytosis may be different in similar geographical conditions, both in humans and animals. It has been related, among other factors, to the decline in the incidence of animal ringworm in these areas or the degree and closeness of animal to human contact [10]. In this article, the occurrence and the main distinctive characteristics of the usual etiological agents of dermatophytosis, both in pets and in farm animals are described. A simple key for the identification of these dermatophytes is included. Dermatophytes in domestic animals