Veterinary Involvement in Zoonotic Dermatophytosis Cases

October 20, 2018
Natalie Stilwell, DVM, MS, PhD

Dr. Natalie Stilwell provides freelance medical writing and aquatic veterinary consulting services through her business, Seastar Communications and Consulting. In addition to her DVM obtained from Auburn University, she holds a MS in fisheries and aquatic sciences and a PhD in veterinary medical sciences from the University of Florida.

A recent case series highlights the importance of screening, as well as treating pets and the home environment after Microsporum canis zoonosis occurs.

Microsporum canis is a globally distributed dermatophyte fungus infecting humans, cats, and dogs. In children, M canis infection (often referred to as ringworm) typically presents as a superficial infection of the scalp and glabrous skin of the limbs and face. Current literature estimates zoonotic transmission from an animal reservoir to occur more frequently than human-to-human transmission.

A recent article in Veterinary Sciences emphasized the importance of veterinary involvement in cases of suspected M canis zoonosis in pediatric patients.

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Zoonotic Transmission of M canis

Three children living in Italy independently developed infection with M canis that presented as tinea corporis, or superficial dermatophytosis on the limbs. In all cases, a pet cat or guinea pig inhabited the child’s home and was subsequently tested by a veterinarian to determine whether it was a reservoir of M canis.

Testing was performed by combing the pet’s entire hair coat with a toothbrush, which was then pressed onto a fungal culture plate. Environmental cultures were also performed in the infected children’s homes using contact plates that were placed on the floor, furniture, and objects in several rooms. Plates were examined daily for 14 days, and fungal growth was identified morphologically to the species level.

Determining Animal Reservoirs

In case 1, veterinarians determined the family’s asymptomatic kitten to be the M canis reservoir. Case 2 involved a pet cat exhibiting epidermal hyperpigmentation. Both cats had recently been adopted or purchased from a breeder, and environmental culture results showed that multiple areas in both households were heavily contaminated with M canis. In case 3, the family’s pet guinea pig and home environment both tested negative for M canis. However, further questioning of the parents revealed the affected child had handled a stray cat 2 weeks before developing lesions.

The infected cats in cases 1 and 2 were treated successfully with oral itraconazole and topical miconazole. Aggressive environmental decontamination of these households included vacuuming, mechanical washing of fabrics, and disinfection of household surfaces with bleach, enilconazole, or peroxidisulfate solution until fungal culture results tested negative.

Important Points to Consider

The authors reported that, although the incidence of human M canis infection has increased significantly in Europe in recent years, most existing literature still fails to properly emphasize animal involvement in human dermatophytosis cases. Thus, these 3 cases highlight several important points to remember about M canis zoonosis.

First, although animals commonly serve as a source of M canis infection in humans, the household pet is not always the culprit. In case 3, the family’s guinea pig tested negative for M canis, while a briefly handled stray cat was identified as the suspected reservoir. Also, case 1 proved that even asymptomatic animals can cause significant environmental contamination of the home, putting other pets and family members at risk of infection. Therefore, thorough cleaning and repeated fungal cultures are important components of M canis management.

Dr. Stilwell received her DVM from Auburn University, followed by a MS in fisheries and aquatic sciences and a PhD in veterinary medical sciences from the University of Florida. She provides freelance medical writing and aquatic veterinary consulting services through her business, Seastar Communications and Consulting.