Genetic Clustering and Virulence Insights in Microsporum canis: Clinical Isolates from US Cats Original paper
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Microbes
Microbes
Microbes, short for microorganisms, are tiny living organisms that are ubiquitous in the environment, including on and inside the human body. They play a crucial role in human health and disease, functioning within complex ecosystems in various parts of the body, such as the skin, mouth, gut, and respiratory tract. The human microbiome, which is […]
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Microsporum canis (M. canis)
Microsporum canis (M. canis)
OverviewMicrosporum canis (M. canis) is a zoophilic dermatophyte common in cats and dogs, responsible for 90% of feline dermatophytoses worldwide.[1][2] It has significant zoonotic potential, transmitting to humans through fomites or direct animal contact, causing severe superficial mycosis. M. canis is considered anthropo-zoophilic and can infect pediatric or immunocompromised patients, causing severe inflammatory responses such […]
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Karen Pendergrass
What was studied?
This study investigated the genetic diversity of Microsporum canis, a dermatophytic fungus that commonly infects cats and is transmissible to humans. Researchers collected 191 fungal isolates from domestic cats across seven US clinics to analyze genotypic variation using eight microsatellite loci, internal transcribed spacer (ITS) sequences, and the mating type (MAT) locus. In addition, the study explored genetic variation in two putative virulence genes: SSU1 and SUB3, which are associated with keratin digestion and adherence.
Who was studied?
A total of 258 hair samples were collected from domestic cats suspected of dermatophytosis, with 191 confirmed M. canis isolates included in the study. The cohort predominantly consisted of kittens (96.8%) from shelter populations (97.4%), most of which were stray, intact domestic shorthairs presenting with alopecic lesions on the head and limbs. Clinical severity was classified based on lesion count, size, and distribution, and was used to correlate with genetic findings.
Most important findings
The study identified substantial genetic variation across the M. canis isolates, observing 122 unique multilocus genotypes from 180 successfully genotyped samples. Notably, three distinct genetic clusters were detected using STRUCTURE and principal component analysis. Clinic location and disease severity were statistically significant predictors of microsatellite variation (p=0.001 and p=0.004, respectively). All isolates were identified as MAT1-1 mating type, supporting prior hypotheses that M. canis populations in the US have largely transitioned to asexual reproduction. No sequence polymorphisms were detected in SSU1 and SUB3, suggesting these genes are highly conserved, likely due to essential roles in virulence.
Key implications
This is the first large-scale genotypic analysis of M. canis in the US and provides foundational evidence that fungal genotype is associated with clinical disease severity. The discovery that all isolates were MAT1-1 indicates a shift toward asexual propagation, which may reduce genetic recombination but stabilize virulent traits within a host population. Identifying conserved virulence genes like SSU1 and SUB3 across diverse isolates supports their potential utility as diagnostic or therapeutic targets. Importantly, the correlation between genotype and clinical presentation, though not definitively causal, suggests that genotyping could eventually inform clinical management strategies, including prognosis and treatment intensity. This work supports the value of expanding to whole-genome sequencing for more granular pathogenicity markers and epidemiological tracking.