Dermatophytosis

First Described: Clinical signs of dermatophytosis date back to the ancient Greek times.1 One of the earliest texts describing the disease in animals was published in 1905.2 Cause: There are over 30 species of dermatophytic fungi, but the most common dermatophytes that cause disease in dogs and cats are Microsporum canis, Nannizzia gypsea (previously Microsporum gypseum), Trichophyton mentagrophytes, and occasionally Microsporum persicolor. Most are zoophilic (and zoonotic) dermatophytes adapted for growth on keratinized structures of animals such as fur, skin cells, and toenails. Affected Hosts: Microsporum canis affects primarily dogs and cats, T. mentagrophytes commonly affects rodents, rabbits, and hedgehogs, and M. persicolor has been described in voles, but all dermatophyte species can infect any host. Nannizzia gypsea is a geophilic dermatophyte species which is usually found in decomposing fur/feathers present in the soil, but can infect living animals after contact with contaminated soil. Geographic Distribution: Dermatophytosis is present worldwide and is most common in warm climates. Route of Transmission: Exposure to spores is needed; dermatophytes are not part of the normal fungal biome. Dermatophytes are most commonly transmitted by direct contact between an infected and uninfected animal; fomite transmission via traumatic inoculation can occur via grooming equipment, bedding, collars, ectoparasites, and exposure to a contaminated environment. Successful fomite infection requires microtrauma to the skin in association with spore exposure. Major Clinical Signs: Clinical signs can be quite variable depending on animal and dermatophyte species involved, and chronicity and location of infection. Lesions commonly found include asymmetrical areas of papules, pustules, crusts, scaling, comedones, and alopecia. Erythema, hyperpigmentation, draining tracts, and nodular dermatitis can occur; as well as onychogryphosis. Pruritus is usually minimal but can sometimes be severe. Lesions can occur anywhere on the body but in cats tend to occur commonly on the face, ears, and paws, and then spread to other areas. Differential Diagnoses: Other causes for follicular infection including bacterial folliculitis and demodicosis, other ectoparasites, pemphigus foliaceus (in cases of severe facial or generalized crusting), and (in cases of nodular dermatitis), neoplasia, deep fungal infection, or mycobacterial granulomas. Dermatophytosis is most common in young animals, animals housed intensely, and/or animals under physiological stress. Human Health Significance: All dermatophytes are potentially zoonotic; Microsporum canis is the species most commonly transmitted from infected animals to humans. People handing infected animals should wear gloves. This is a low-level zoonotic disease and causes skin lesions in people; it is curable and infection is not life-threatening. Complications of animal-origin infections are rare, and when infection occurs in immunosuppressed people the most common potential adverse effects are those associated with prolonged treatment.3-5 Most serious dermatophyte infections in people are of human origin and involve human pathogens.3-5