IN ANIMALS continued
environmental conditions. 3,5 In most immunocompetent hosts, dermatophytosis is a self-limiting disease.
or fungal culture. 5 False-negative results with Wood’s lamp examination may occur as fluorescence is only seen with dermatophytosis due to M. canis , and not all M. canis isolates will fluoresce. • PCR detection of dermatophytes is difficult to interpret as a positive PCR does not necessarily indicate an active infection. 5
DIAGNOSIS • Diagnosis of dermatophytosis is based on clinical
suspicion in conjunction with the results of Wood’s lamp and direct examination to document active hair infection and/
TRANSMISSION
• The main mode of transmission of M. canis is through direct or indirect contact with the coat or skin lesions of infected animals. • Contact with accumulated scale and hair in the environment and fomites (including furniture, linen, brushes etc.) are also potential sources. Contact with a contaminated environment in the absence of concurrent skin trauma is considered a rare source of infection for humans and animals. 5
IN HUMANS
PREVALENCE AND RISK FACTORS • Dermatophytes are grouped as either anthropophilic, zoophilic or geophilic depending on whether their primary source is human, animal or environmental, respectively. Whilst dermatophytosis is a common skin disease in people, the rate of transmission from companion animals to humans is unknown. • Microsporum canis is a causative pathogen for the human dermatophyte skin infections tinea capitis (infection of the scalp, hair follicles and surrounding skin) and tinea corporis (infection of glabrous skin, with lesions that may involve the trunk, neck, arms and legs). • It is estimated that approximately 50% of humans exposed to M. canis infected cats acquire the infection, and in 30-70% of households with an infected cat at least one cohabitating human will become infected. 10 • Data on human skin infections with M. canis in Australia is limited. Melbourne data on 12,316 dermatophyte isolates collected during 1996–1998 found that M. canis was responsible for 75% of laboratory-diagnosed tinea capitis cases. 11 A review of superficial fungal cultures submitted to a commercial laboratory in 2013 identified 7.4% of the culture-positive samples as zoophilic dermatophytes, with equal numbers of M. canis and Trichophyton interdigitale . 12 Zoophilic fungal infections were more likely in younger patients. • Tinea corporis can be caused by various dermatophyte species, however patients in close contact with companion animals are
Ringworm lesions on the face and arms of a child (Courtesy of Prof. Richard Malik)
commonly infected with M. canis. The incubation period is 1-3 weeks. 13 It occurs most frequently in post-pubertal children and young adults, with children more likely to contract zoophilic infections through contact with pets. 13 CLINICAL DISEASE • Tinea corporis typically presents as a well- demarcated, single or multiple, oval or circular, mildly erythematous lesion with a raised border (the characteristic ‘ringworm’ lesion). Varying levels of pruritus may be present. In immunocompromised individuals, tinea corporis can present as a disseminated skin infection or as a subcutaneous/deep abscess. 13
CONTENTS
69 Companion Animal Zoonoses Guidelines
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