Trichophyton species and Microsporum gypseum infection and fomite carriage in cats from three animal shelters: a retrospective case series

Abstract

Objectives

The goal of this retrospective case series was to report on the clinical aspects of confirmed Trichophyton species and Microsporum gypseum infections in cats from three animal shelters

Methods

This was an observational retrospective study. Fungal culture and treatment data from three animal shelters was retrospectively reviewed to identify cats with dermatophytosis caused by Trichophyton species or M gypseum.

Results

Among the three shelters only four cats were diagnosed with M gypseum dermatophytosis. With respect to Trichophyton species infections, there were six cases identified and treated in a 1 year period in one shelter, 13 cases over 13 years in the second shelter and 27 cases over 5 years in the third shelter. Four cases of M gypseum dermatophytosis were treated in the third shelter. Young cats were most commonly infected and the disease was most commonly diagnosed in the fall and winter months. Lesions were inflammatory and found predominantly on the head and neck. There was a rapid response to treatment in all cases; mean (n = 20) and median (n = 17) days to mycological cure were calculated from available data. Fungal culture data revealed fomite carriage without clinical evidence of infection for Trichophyton species (n = 43) cats and M gypseum (n = 37) cats.

Conclusions and relevance

There is a paucity of clinical information about non-Microsporum canis dermatophytosis in shelter cats. This study data shows that Trichophyton species and M gypseum infections do occur but are uncommon. Based upon the rapid response to conventional treatment, these infections do not represent a treatment challenge, as most cats reached mycological cure within 3 weeks.

Introduction

Dermatophytosis is a superficial fungal skin disease and is the most common infectious and contagious skin disease of cats. Although the disease is not life threatening and is self-limiting in most cats, it is an important disease to recognize and treat in order to limit contagion. The overall prevalence of the disease is low, but it is more common in kittens and cats from situations in which the population density is high; for example, animal shelters or rescue organizations.^1,2

The most commonly isolated pathogen from cats is Microsporum canis. Less commonly isolated species include zoophilic species, such as Trichophyton, and geophilic species (ie, Microsporum gypseum) as possible causes of clinical disease, but reports of confirmed cases or case series are limited.^3–5 The goal of this retrospective case series was to report on the clinical aspects of confirmed Trichophyton species and M gypseum infections in cats from three animal shelters.

Materials and methods

Institutional approval

This was a retrospective clinical case report; however, all authors had appropriate institutional and/or organizational approval for the work described.

Laboratory methods

Fungal cultures from shelters 1 and 2 were processed at the University of Wisconsin, School of Veterinary Medicine Dermatology Research Laboratory. Tooth-brush fungal cultures were inoculated onto 90 mm plates containing a selective fungal culture medium (Mycosel agar [Becton Dickinson] with added phenol red as a color indicator), incubated at 25–27°C for 21 days and examined daily for growth. Suspect colonies were confirmed as pathogens by microscopic examination. Toothbrush fungal cultures from shelter 3 were handled similarly, except that commercial Dermatophyte Test Mediums were used. Staff members were trained in fungal culture procedures and microscopic identification.

Number of days to mycological cure

The number of days to mycological cure was calculated from the start of treatment to the date of the second negative culture. It excluded a 21 day holding period to finalize cultures.

Treatment protocols

All of the cats were treated with 5–10 mg/kg itraconazole PO q24h for 14–28 days with concurrent, twice-weekly topical antifungal rinses of either lime sulfur rinses or accelerated hydrogen peroxide shampoo (Pure Oxygen Ultra Shampoo; Ogena Solutions) to disinfect the haircoat. Cats were housed in cages alone or with littermates, depending upon shelter management policy.

Data analysis

This was a clinical case series and descriptive data are reported.

Results

Shelter 1

This was a limited access shelter in the Midwestern United States and cats were selected for admission based upon space, high probability of being adopted and overall health. One year’s worth of data were available for review (2003–2004) during which 241 cats were admitted into the shelter and six cases of Trichophyton species dermatophytosis were diagnosed (Table 1). Lesions presented as scaling, crusting and erythema on the ears, ear margins and face, and infection was confirmed via growth of Trichophyton species colonies on toothbrush fungal culture. All infected cats were <6 months of age. Four of six cases occurred in the winter months (September–February) and two occurred in July. These latter two cases were littermates that were acquired from a farm. Owing to cost constraints, the first post-treatment fungal culture was obtained after 4 weeks of treatment. All six cats were culture negative after 4 weeks of treatment and remained culture negative on two subsequent weekly cultures.

Table 1

Summary of Trichophyton species and Microsporum gypseum infections or fomite carriage cases at three animal shelters

	Shelter 1Midwestern United States(intake 241)	Shelter 2Midwestern United States(intake >2000/year)	Shelter 3Western United States(intake >3200/year)	Total
Trichophyton species-infected cats	6	13	27	56
Microsporum gypseum-infected cats	0	0	4	4
Trichophyton species fomite carriage	0	29	14	43
Microsporum gypseum fomite carriage	0	33	4	37

Shelter 2

This was an open admission shelter in the Midwestern United States admitting >2000 cats per year. See Table 1 for a summary of the data. Between 2003 and 2016, 13 cats were diagnosed with dermatophytosis caused by Trichophyton species. By comparison, during this same time period 611 cats were diagnosed with M canis dermatophytosis. Lesions were noted as inflammatory, alopecic, severely crusted and/or markedly erythematous and located on the ear, ear margins and face (Figures 1 and 2). Infected cats were juveniles. Except for one case diagnosed in July, all others were diagnosed between November and January. Review of the weekly fungal culture data showed that mean and median number of days to mycological cure were 21 and 17, respectively (range 17–35 days). During this study period, 29 and 33 cats were diagnosed with Trichophyton species and M gypseum fomite carriage, respectively. These cats were lesion-free during the study period but had one initial positive fungal culture. Repeat toothbrush fungal cultures from these cats were negative and remained so.

Figure 1

Cat with Trichophyton species infection. Note the inflammatory lesions on the muzzle

Figure 2

Cat with Trichophyton species infection. Note the inflammatory lesion on the nasal planum and above the left eye

Shelter 3

This was a transfer-in limited admission shelter in the Western United States admitting approximately 3200 cats per year. See Table 1 for a summary of the data. Between 2013 and 2018, data review identified 27 cats diagnosed with Trichophyton species dermatophytosis (Table 1). Affected cats were all kittens and had inflammatory lesions most commonly on the face, ears and/or digits. In 22/27 cats, cases were diagnosed from August to December; five additional cases were diagnosed in March (n = 1), May (n = 3) and July (n = 1). Review of weekly fungal culture data showed that the mean and median time to mycological cure were 19 and 17 days, respectively (range 12–36 days). Four cats were diagnosed with M gypseum dermatophytosis. All of the cats had lesions on their face and ears and one cat also had lesions on the tarsus and digits. The mean and median number of days to mycologic cure were 13.5 days (range 12–16 days). During the study period 14 and four cats were identified as having Trichophyton species and M gypseum fomite carriage, respectively. These cats were lesion-free but had one initial positive fungal culture. Toothbrush fungal cultures from these cats were negative the next week and remained so; these cats did not develop lesions.

Discussion

There were several clear trends found in examining the data from these three shelters. First, Trichophyton species and M gypseum infections were uncommon. Similarly to M canis infections, ² young cats were most commonly affected. In these three shelters from the United States, cases were most commonly diagnosed in the fall and winter months and uncommonly during other seasons. Lesions were located predominantly on the head and ears and were consistently inflammatory. Cats responded quickly to treatment. In the first shelter, cats were all culture negative by week four of treatment. In shelters 2 and 3, cats also recovered quickly. Pooled time to cure data revealed a mean, median and range of 20, 17 and 12–36 days, respectively. The four cats diagnosed with M gypseum infection also had a rapid response to treatment. The higher occurrence of dermatophytosis in shelter 3 is likely due to the higher intake of animals per year, referral for treatment and/or different geographic location than shelters 1 and 2.

In this study, 43 and 37 cats with positive Trichophyton species or M gypseum fungal cultures were diagnosed as having fomite carriage. All cats were lesion-free, had a single positive culture at intake, follow-up fungal cultures were negative and cats were not reported to develop skin lesions. This pattern is consistent with fomite carriage; however, we do recognize that it is possible that some of these cats may have had true infections with either pathogen prior to being surrendered to the shelters and had spontaneously resolving infections.

The source of the exposure for either true infection or fomite carriage for M gypseum is presumed to be the soil as this is a geophilic organism. ⁶ For Trichophyton species it is believed that exposure is from contact with infected hosts, primarily other cats, wild animals, rodents or the soil. In one case series, 12/14 cats infected with species of the Trichophyton mentagrophytes complex were described as ‘hunters’ by their owners. ⁷

There are several limitations of this study. The first and most obvious is that the study findings are retrospective and therefore inherently less meaningful than prospective studies. Nevertheless, there is a paucity of clinical data on the prevalence of Trichophyton species or M gypseum infections in shelter situations relative to M canis dermatophytosis. Second, Trichophyton species are difficult to identify microscopically, and it is possible that these study results underestimate the commonality of Trichophyton species infections. Fur-thermore, Trichophyton species infections are limited to a genus-level diagnosis, and therefore this retrospective analysis lacks details regarding the potential impacts of species-specific infection treatment and management of culture-positive animals. Identification of suspect dermatophyte colonies by PCR is increasingly becoming the norm; however, this test was not available or affordable during the study period. ⁷ Third, it could be argued that in-house cultures are inferior to use of a reference laboratory; however, a recently published study found that there is less than a 3% chance of error with point-of-care fungal cultures when users adhere to proper procedures of storage and observation of gross and microscopic examination of plates. ⁸

This study did identify an important problem with dermatophyte infections in shelter cats: how to differentiate fomite carriage from true infection. In this study, repeat cultures was the option used, but this is an expensive option (ie, cost of repeat cultures, increased animal care days and increased confinement of cats). Another option is to perform direct examinations on suspect lesions. Direct examinations of hair and scale scraped from suspect lesions allow for rapid confirmation of disease, as shown in a recent study. ⁹ This technique is not difficult to master but does require practice. Once learned it is an inexpensive way to help make this differentiation.

Conclusions

There is a paucity of clinical information on non-M canis dermatophytosis in shelter cats. This study data found that Trichophyton species and M gypseum infections are uncommon. Lesions occur most commonly in young cats in the winter and are characterized by inflammatory lesions on the head and ears. Cats in this study showed a rapid response to treatment.