Abstract
Objectives
The aim of the study was to determine the prevalence of dermatophyte shedding in cats admitted to three Ontario animal shelters from February to May 2013.
Methods
Four hundred cats were sampled within 48 h of admission, using a standard toothbrush sampling technique. Dermatophyte culture was performed.
Results
Dermatophytes were not identified in any of the 400 cats (0–0.9% one-sided exact 97.5% confidence interval).
Conclusions and relevance
These results imply that dermatophyte shedding is rare in cats admitted to Ontario animal shelters. Consequently, identification of infected animals, particularly multiple animals, represents an unusual occurrence that may justify prompt and intensive control measures.
Introduction
Dermatophytosis (ringworm) is a common and highly transmissible fungal skin infection of various animal species.1–4 While typically self-limiting, disease can be prolonged and because of the highly transmissible nature, infected cats and subclinical carriers can pose a risk to humans and animals. Dermatophytosis is an important shelter-associated infection and outbreaks can lead to widespread infection of animals (especially cats), human health risks and profound disruption of shelter activities, including shelter closure and high economic costs associated with disease control measures. While it should rarely be required to control adequately even large outbreaks, depopulation is sometimes used as a control measure. Therefore, prevention and control of dermatophytosis is an important component of animal shelter infection control. One component of dermatophyte control that can be used is screening of animals for dermatophyte shedding. Screening can occur in response to clinical signs, as a routine infection control tool or as an outbreak response measure. For any surveillance activity, having a plan to use the surveillance data is a key component in making sound epidemiological and clinical decisions.
Published data regarding dermatophyte shedding in healthy cats are limited. While subclinical carriers are important sources of dermatophytes, prevalence data are relatively limited and quite variable. For example, a study of colony and pet cats in south-east England reported dermatophytes in 4.3% of clinically normal cats, 5 while 13% of pet and 100% of stray cats were positive in a study in central Italy. 6 A more recent study of stray cats in Italy reported dermatophyte shedding by 5.5% of 273 cats caught as part of a trap–neuter–release program, 7 similar to the prevalence reported in earlier studies of shelter cats from the USA (4–5%).8,9 However, little has been reported about dermatophyte shedding by animals in shelters, and it is unclear whether data pertaining to pet or feral cats adequately reflect this shelter population.
As various animal, geographic, environmental, animal management and related factors could affect the prevalence of dermatophyte shedding in a shelter population, population- and region-specific data are required to ensure that clinical and surveillance results are put into the proper context. The objective of this study was to determine the prevalence of dermatophyte shedding in cats admitted to three Ontario animal shelters.
Materials and methods
A prospective observational study was designed involving cats from three participating animal shelters (Guelph Humane Society, Kitchener-Waterloo Humane Society and Toronto Humane Society) in Ontario, Canada, with data collected from 1 February to 31 May 2013. On average, 1000–4000 cats are admitted to each of these shelters annually. The Toronto Humane Society was located in a large metropolitan area, while the Guelph and Kitchener-Waterloo Humane Societies were located in smaller (population approximately 100,000) cities with animals admitted from both urban and adjacent rural areas. All cats that were admitted to the shelters during the study period were eligible for enrolment until the target sample size was achieved. Cats that were too sick, injured or fractious to safely and humanely sample were excluded. For the Toronto and Kitchener-Waterloo shelters, 150 cats were serially enrolled. Because of a lower admission rate during the study period, 100 animals were enrolled from the Guelph Humane Society. The University of Guelph Animal Care Committee approved all procedures and protocols used in this study.
Sampling was performed within 48 h of admission. Clean, unused toothbrushes were brushed over the surface of the entire haircoat for at least 1 min, with particular attention paid to the head and face. 10 A new set of nitrile gloves was worn during handling and sampling of each animal. If skin lesions were present, the clinically unaffected part of the body was sampled first followed by the lesion-covered areas, using the same toothbrush.
Toothbrushes were immediately placed in individual sealable plastic bags. Samples were stored at room temperature and transported to the study laboratory. Toothbrushes were inoculated onto Mycosel agar, which was incubated at 25.8°C. The plates were checked once a week for 3 weeks for the presence of colonies with an appearance similar to that of dermatophytes. A control strain of Microsporum canis (ATCC 9865) was cultured in parallel. Suspicious colonies were examined cytologically by using adhesive tape to collect material from the colony followed by staining with methylene blue. 10 DNA was extracted from suspicious colonies using a commercial kit (InstaGene Matrix; BioRad Laboratories) and used as the template for a PCR assay that detects and differentiates M canis from other common dermatophytes. 11 Positive (M canis ATCC 9865) and negative controls were included with each run. Additionally, the degree of non-dermatophyte growth was recorded subjectively as no growth (NG), low contaminant growth, moderate contaminant growth or high contaminant growth. 10
Dermatophyte prevalence and 95% exact confidence intervals (CIs) were estimated. If the prevalence was 0% or 100% then the 97.5% one-sided exact CI was reported. For each cat sampled, age, sex, breed, source, hair length, date of admission and the presence or absence of skin lesions were recorded and described.
Results
Demographic characteristics of the study population are described in Table 1. Dermatophytes were not identified in any of the 400 samples during the study period (0–0.9%, 97.5% one-sided exact CI). The 97.5% one-sided exact CIs for the shelters that sampled 150 cats (n = 2 shelters) and 100 cats (n = 1 shelter) were 0–2.4% and 0–3.6%, respectively. Positive control samples tested in parallel all yielded M canis. Dermatophytosis was not identified by shelter personnel in any animal in any of the three shelters during the study period.
Demographic characteristics of 400 cats tested for the presence of dermatophytes at the time of presentation to one of three animal shelters in Ontario, Canada (1 February to 31 May 2013)
Includes both known and estimated ages
Includes cats that were transferred from other shelters, rescued cats, those returned from adoption and feral cats
DSH = domestic shorthair; DMH = domestic mediumhair; DLH = domestic longhair; NA = not applicable
While dermatophytes were not identified, various other fungi were isolated. Overall, 60.8% (95% CI 55.7–65.5%), 15.8% (95% CI 12.3–19.7%) and 8.5% (95% CI 6.0–11.7%) of samples had low, moderate and high levels of non-dermatophyte growth, respectively.
Discussion
Dermatophyte colonization was not identified in any cat in this study, despite sampling a large number of cats from different shelters, suggesting that dermatophyte colonization is rare in cats admitted to shelters in this region. Poor sample quality is another potential explanation, but the abundant fungal organisms of other types that were found here suggest that sampling was adequate. Another potential explanation is overgrowth of other fungi on plates, yet heavy growth of other fungi was uncommon. The culture medium that was chosen is a commonly used medium for isolation of dermatophytes and the control M canis strain grew well, ruling out problems with media selection and quality. Therefore, while no sampling and culture method can be assumed to be 100% sensitive, it is likely that the lack of dermatophyte isolation in this study is representative of the state of this population.
The results of this study have given insight into the endemic prevalence of colonization in cats admitted to three Ontario animal shelters. With the 0% prevalence identified here, it is apparent that dermatophyte colonization is uncommon in cats in this population. Clinical ringworm infections are relatively uncommon in these shelters, but are identified sporadically. Because of the potential for outbreaks in shelters and zoonotic transmission to shelter personnel or adopting families, an aggressive response to clinical ringworm cases is often taken. As this may include testing a sample or all cats in the population, understanding the baseline (‘expected’) dermatophyte prevalence is critical for proper interpretation of outbreak testing. Based on the data from this study, finding any colonized cats or at most a prevalence exceeding 2–4%, based on the prevalence and CIs estimated, could be considered an unusual situation in these shelters (and perhaps the broader region), and justify a comprehensive response. This would be in contrast to areas with high endemic rates where finding colonized cats would more likely reflect the endemic nature of the disease rather than an abnormal situation.
The high incidence of skin lesions in the absence of dermatophytosis is also important to consider, particularly in a study population that comprised largely young cats during winter, when the incidence of dermatophytosis may be higher. Over-reaction to the presence of skin lesions in cats can occur in shelters, and these data emphasize the need for understanding the epidemiology of dermatophytosis in individual regions and the need for proper testing and infection control practices in shelters, to balance ringworm prevention and over-reaction.
The limitations of this study must be considered. All of the shelters included in this study were located within approximately 100 km of each other in Ontario. Consequently, it may not be appropriate to extrapolate these results to different regions of Ontario or other provinces in Canada. In addition, shelters can be highly variable in terms of physical layout, caseload, staffing, baseline infection control practices and various other factors. All three shelters studied here were anecdotally considered to be well-resourced and well-operated facilities, and results could be different in shelters with greater economic, infrastructure, personnel or operational challenges. Also, testing was performed during one time of year (February to May 2013), and it is possible that the prevalence could be different during warmer times of the year.12,13
Conclusions
A clear understanding of the epidemiology of dermatophytosis (and other infectious diseases) is a key component of shelter disease control. Monitoring studies such as this, while potentially time consuming and costly, can provide critical data for the development and interpretation of infection control measures. Data from this study indicate that dermatophyte shedding is rare in cats presented to shelters in this region; this is an important finding for interpreting surveillance data and setting thresholds for comprehensive disease control activities.
Footnotes
Acknowledgements
We would like to thank the Guelph, Kitchener-Waterloo and Toronto Humane Societies for their cooperation and for sampling the cats at their respective shelters.
Conflicts of interest
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
This study was supported by Dr Weese’s Canada Research Chair in zoonotic diseases.