Dermatophytes are highly infectious fungi that cause superficial infections in keratinized tissues in humans and animals. This group of fungi is defined by their ability to digest keratin and encompasses a wide range of species. Classification of many of these species has recently changed due to genetic analysis, potentially affecting clinical diagnosis and disease management. In this review, we discuss dermatophyte classification including name changes for medically important species, current and potential diagnostic techniques for detecting dermatophytes, and an in-depth review of Microsporum canis, a prevalent zoonotic dermatophyte. Fungal culture is still considered the “gold standard” for diagnosing dermatophytosis; however, modern molecular assays have overcome the main disadvantages of culture, allowing for tandem use with cultures. Further investigation into novel molecular assays for dermatophytosis is critical, especially for high-density populations where rapid diagnosis is essential for outbreak prevention. A frequently encountered dermatophyte in clinical settings is M. canis, which causes dermatophytosis in humans and cats. M. canis is adapting to its primary host (cats) as one of its mating types (MAT1-2) appears to be going extinct, leading to a loss of sexual reproduction. Investigating M. canis strains around the world can help elucidate the evolutionary trajectory of this fungi.

Bartonellae are emerging blood-borne bacteria that have been recovered from a wide range of mammalian species and arthropod vectors around the world. Bats are now recognized as a potential wildlife reservoir for a diverse number of Bartonella species, including the zoonotic Candidatus B. mayotimonensis. These bat-borne Bartonella species have also been detected in the obligate ectoparasites of bats, such as blood-feeding flies, which could transmit these bacteria within bat populations. To better understand this potential for transmission, we investigated the relatedness between Bartonella detected or isolated from bat hosts sampled in Mexico and their ectoparasites. Bartonella spp. were identified in bat flies collected on two bat species, with the highest prevalence in Trichobius parasiticus and Strebla wiedemanni collected from common vampire bats (Desmodus rotundus). When comparing Bartonella sequences from a fragment of the citrate synthase gene (gltA), vector-associated strains were diverse and generally close to, but distinct from, those recovered from their bacteremic bat hosts in Mexico. Complete Bartonella sequence concordance was observed in only one bat-vector pair. The diversity of Bartonella strains in bat flies reflects the frequent host switch by bat flies, as they usually do not live permanently on their bat host. It may also suggest a possible endosymbiotic relationship with these vectors for some of the Bartonella species carried by bat flies, whereas others could have a mammalian host.

Microsporum canis is the primary agent causing dermatophytosis in cats, and also infects humans, dogs, and other species. Assessment of genetic variation among M. canis isolates in the United States has not been conducted. Further, M. canis mating type and assessment of disease severity associated with genotypic characteristics have not been rigorously evaluated. We therefore isolated M. canis from 191 domestic cats across the US and characterized genotypes by evaluation of ITS sequence, MAT locus, and microsatellite loci analysis. The genes SSU1 and SUB3, which are associated with keratin adhesion and digestion, were sequenced from a subset of isolates to evaluate potential genetic associations with virulence. Analysis of microsatellite makers revealed three M. canis genetic clusters. Both clinic location and disease severity were significant predictors of microsatellite variants. 100% of the M. canis isolates were MAT1-1 mating gene type, indicating that MAT1-2 is very rare or extinct in the US and that asexual reproduction is the dominant form of replication. No genetic variation at SSU1 and SUB3 was observed. These findings pave the way for novel testing modalities for M. canis and provide insights about transmission and ecology of this ubiquitous and relatively uncharacterized agent.

In the last decade, pulmonary fungal infections such as invasive pulmonary aspergillosis (IPA) have increased in incidence due to the increased number of immunocompromised individuals. This increase is especially problematic when considering mortality rates associated with IPA are upwards of 70%. This high mortality rate is due to, in part, the length of time it takes to diagnose a patient with IPA. When diagnosed early, mortality rates of IPA decrease by as much as 30%. In this review, we discuss current technologies employed in both medical and research laboratories to diagnose IPA, including culture, imaging, polymerase chain reaction, peptide nucleic acid–fluorescence in situ hybridization, enzyme-linked immunosorbent assay, lateral flow assay, and liquid chromatography mass spectrometry. For each technique, we discuss both promising results and potential areas for improvement that would lead to decreased diagnosis time for patients suspected of contracting IPA. Further study into methods that offer increased speed and both analytical and clinical sensitivity to decrease diagnosis time for IPA is warranted.

Dermatophytosis is a superficial fungal infection of keratinized tissues that can occur in humans and other animals. In domestic cats, the majority of cases are caused by Microsporum canis and can spread to other animals and humans via arthrospores. Between 2019 and 2021, 164 cases of suspected dermatophytosis were recorded in animals from a high-volume shelter in California. Samples (hair, nail, and skin scraping) were collected for routine screening from these individuals. One hundred and twenty-six of these were diagnosed as M. canis by culture and internal transcribed spacer (ITS) sequence. In four suspected dermatophytosis cases occurring in kittens in 2019, cultures grown at 20°C yielded fungi with colony morphology more similar to Arthroderma species than Microsporum. Morphologic and microscopic examinations were conducted, and gene segments for the ITS, β-tubulin, and translation elongation factor 1-alpha (TEF1) regions were sequenced from DNA extracted from these cultures. Sequences were aligned to other dermatophytes using maximum likelihood and neighbor-joining trees and were compared to previously described fungal species to assess nucleotide homology. We identified two previously undescribed fungal species, herein proposed as Arthroderma lilyanum sp. nov. and Arthroderma mcgillisianum sp. nov. M. canis co-cultured in two of the four cases. Other physiologic tests supported this diagnosis. These species have significance as potential pathogens and should be considered as rule-outs for dermatophytosis in cats. The potential for infection of other species, including humans, should be considered. Two novel fungal species were cultured and characterized from four cases of suspected ringworm in cats at an animal shelter in CA, US. These species were genetically distinct from other dermatophytes and are herein described as Arthroderma lilyanum sp. nov. and Arthroderma mcgillisianum sp. nov.

We evaluated enzyme-linked immunosorbent assay (ELISA) specificity for measuring seroantibody responses to two types of retroviral infections in domestic cats: feline immunodeficiency virus (FIV) and feline foamy virus (FFV). We compared the seroreactivity of specific pathogen-free (SPF) cat sera, sera from SPF cats inoculated with either FIV or FFV, and field isolates (e.g., shelter or privately owned cats). Sera from SPF cats experimentally infected with the cognate virus had significantly lower background in both FIV and FFV ELISAs compared to sera from negative field isolates. ELISA values for SPF cats exposed to either FIV or FFV tended to have higher OD values on the opposite ELISA antigen plate. FIV nonspecific background absorbance was greater than that of FFV, and 10 of 15 sera samples from FIV seronegative field samples were measured in the indeterminant range. These findings highlight that exposure to off-target pathogens elicit antibodies that may nonspecifically bind to antigens used in binding assays; therefore, validation using sera from SPF animals exposed during controlled infection results in the setting of a cutoff value that may be inappropriately low when applied to field samples. Our work also suggests that infection of domestic cats with pathogens other than FIV results in antibodies that cross-react with the FIV Gag antigen.