Retrospective Comparison of Polymerase Chain Reaction and Culture-Based Identification for Diagnosis of Microsporum canis and Trichophyton Spp. in Shelter Cats and Dogs

Wesley Cheung; Alexandre Ellis; Amanda Idle; Alexandra Protopopova; Emilia Gordon

doi:10.56771/jsmcah.v3.86

Authors

Wesley Cheung Ontario Veterinary College, Department of Clinical Studies Guelph, Ontario, Canada
Alexandre Ellis Shelter Outreach Consultation Services, Calgary, AB, Canada https://orcid.org/0000-0003-2773-2087
Amanda Idle Haven Veterinary Services, Vancouver, BC, Canada
Alexandra Protopopova Animal Welfare Program, Faculty of Land and Food Systems, The University of British Columbia, Vancouver, BC, Canada https://orcid.org/0000-0001-9992-3101
Emilia Gordon Haven Veterinary Services, Vancouver, BC, Canada https://orcid.org/0009-0005-9798-0328

DOI:

https://doi.org/10.56771/jsmcah.v3.86

Keywords:

ringworm, dogs, cats, shelter medicine, diagnostic methods, Public Health

Abstract

Introduction: Canine and feline dermatophytosis is challenging to manage in shelter settings because of its transmissibility, potential for zoonosis and labour-intensive treatment. An efficient and accurate initial diagnostic plan is essential to confirm infection, prevent outbreaks and ensure public safety. While quantitative polymerase chain reaction (PCR) has gained attention for its rapid turnaround time, studies have shown variable sensitivity. This study aimed to assess the performance of PCR in detecting Microsporum canis and Trichophyton spp. in shelter cats and dogs when compared to culture-based identification.

Methods: Between 1 June 2015 and 10 January 2023, 125,939 cats and dogs entered 34 sheltering locations in coastal Western Canada. Of these, 246 animals (48 dogs, 198 cats) had both culture and PCR results, and sufficient records for analysis. Toothbrush samples were collected for dermatophyte test medium (DTM)/enhanced sporulation agar (ESA) bi-plates at a central shelter location and submitted for PCR at a referral laboratory before treatment was initiated. The diagnostic accuracy of PCR was evaluated using the reference standard of a 14-day culture result combined with P-scoring, a semi-quantitative method to assess DTM culture colonies.

Results: Culture readings identified 72/246 (29.27%) lesional animals as positive (63 cats [31.81%] and 9 dogs [18.75%]). PCR demonstrated an overall sensitivity of 86.1% and specificity of 94.8% for both animal species combined. PCR for M. canis showed a sensitivity of 86.4% and a specificity of 97.8%, while PCR for Trichophyton spp. showed a sensitivity of 84.6% and specificity of 97.9%. DTM/ESA culture was highly efficient, with positive results available within 7 days for most cases (59/63 cats [93.6%] and 9/9 dogs [100%]).

Conclusion: The variability in dermatophyte PCR sensitivity across recent studies highlights the risks of reliance on PCR as a sole diagnostic tool for suspect animals, especially when considering the demonstrated efficacy of in-house culture.

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