Mitochondrial DNA variants and microbiota: An experimental strategy to identify novel therapeutic potential in chronic inflammatory diseases.

We previously demonstrated that mice carrying natural mtDNA variants of the FVB/NJ strain (m.7778 G>T in the mt-Atp8 gene in mitochondrial complex V), namely C57BL/6 J-mtFVB/NJ (B6-mtFVB), exhibited (i) partial protection from experimental skin inflammatory diseases in an anti-murine type VII collagen antibody-induced skin inflammation model and psoriasiform dermatitis model; (ii) significantly altered metabolites, including short-chain fatty acids, according to targeted metabolomics of liver, skin and lymph node samples; and (iii) a differential composition of the gut microbiota according to bacterial 16 S rRNA gene sequencing of stool samples compared to wild-type C57BL/6 J (B6) mice. To further dissect these disease-contributing factors, we induced an experimental antibody-induced skin inflammatory disease in gnotobiotic mice. We performed shotgun metagenomic sequencing of caecum contents and untargeted metabolomics of liver, CD4+ T cell, and caecum content samples from conventional B6-mtFVB and B6 mice. We identified D-glucosamine as a candidate mediator that ameliorated disease severity in experimental antibody-induced skin inflammation by modulating immune cell function in T cells, neutrophils and macrophages. Because mice carrying mtDNA variants of the FVB/NJ strain show differential disease susceptibility to a wide range of experimental diseases, including diet-induced atherosclerosis in low-density lipoprotein receptor knockout mice and collagen antibody-induced arthritis in DBA/1 J mice, this experimental approach is valuable for identifying novel therapeutic options for skin inflammatory conditions and other chronic inflammatory diseases to which mice carrying specific mtDNA variants show differential susceptibility.

Effects of Outdoor-Grown Royal Sun Medicinal Mushroom Agaricus brasiliensis KA21 (Agaricomycetes) Fruiting Body on Canine Malassezia Dermatitis.

Brazil-grown outdoor-cultivated Agaricus brasiliensis KA21 fruiting body (KA21) significantly increases the production of serum anti-beta-glucan antibody. Therefore, KA21 ingestion may be useful for the prevention and alleviation of fungal infections. This study aimed to determine the effects of KA21 in fungal infections in animals. KA21 was administered to nine dogs infected with Malassezia. Notably, the anti-beta-glucan antibody titer remained unchanged or tended to decrease in the oral steroid arm, whereas in the non-steroid arm, antibody titer increased in almost all animals after KA21 ingestion. Dogs showing improved clinical symptoms exhibited increased anti-beta-glucan antibody titers. The results of this study suggest that KA21 ingestion may alleviate the symptoms of Malassezia and other fungal infections and that continuous ingestion may help prolong recurrence-free intervals. Additionally, the ingestion of KA21 during oral steroid dosage reduction or discontinuation may enable smoother steroid withdrawal.

Prevalence and genetic diversity of azole-resistant Malassezia pachydermatis isolates from canine otitis and dermatitis: A 2-year study.

Despite previous reports on the emergence of Malassezia pachydermatis strains with decreased susceptibility to azoles, there is limited information on the actual prevalence and genetic diversity of azole-resistant isolates of this yeast species. We assessed the prevalence of azole resistance in M. pachydermatis isolates from cases of dog otitis or skin disease attended in a veterinary teaching hospital during a 2-year period and analyzed the ERG11 (encoding a lanosterol 14-α demethylase, the primary target of azoles) and whole genome sequence diversity of a group of isolates that displayed reduced azole susceptibility. Susceptibility testing of 89 M. pachydermatis isolates from 54 clinical episodes (1-6 isolates/episode) revealed low minimum inhibitory concentrations (MICs) to most azoles and other antifungals, but 11 isolates from six different episodes (i.e., 12.4% of isolates and 11.1% of episodes) had decreased susceptibility to multiple azoles (fluconazole, itraconazole, ketoconazole, posaconazole, ravuconazole, and/or voriconazole). ERG11 sequencing of these 11 azole-resistant isolates identified eight DNA sequence profiles, most of which contained amino acid substitutions also found in some azole-susceptible isolates. Analysis of whole genome sequencing (WGS) results revealed that the azole-resistant isolates from the same episode of otitis, or even different episodes affecting the same animal, were more genetically related to each other than to isolates from other dogs. In conclusion, our results confirmed the remarkable ERG11 sequence variability in M. pachydermatis isolates of animal origin observed in previous studies and demonstrated the value of WGS for disentangling the epidemiology of this yeast species.

We analyzed the prevalence and diversity of azole-resistant Malassezia pachydermatis isolates in a veterinary hospital. A low prevalence of multi-azole resistance (c.10% of isolates and cases) was found. Whole genome and ERG11 sequencing of resistant isolates revealed remarkable genetic diversity.

Discovery of novel treponemes associated with pododermatitis in elk (Cervus canadensis).

Pododermatitis, also known as treponeme-associated hoof disease (TAHD), presents a significant challenge to elk (Cervus canadensis) populations in the northwestern USA, with Treponema spp. consistently implicated in the lesion development. However, identifying species-specific Treponema strains from these lesions is hindered by its culture recalcitrance and limited genomic information. This study utilized shotgun sequencing, in silico genome reconstruction, and comparative genomics as a culture-independent approach to identify metagenome-assembled Treponema genomes (MATGs) from skin scraping samples collected from captive elk experimentally challenged with TAHD. The genomic analysis revealed 10 new MATGs, with 6 representing novel genomospecies associated with pododermatitis in elk and 4 corresponding to previously identified species-Treponema pedis and Treponema phagedenis. Importantly, genomic signatures of novel genomospecies identified in this study were consistently detected in biopsy samples of free-ranging elk diagnosed with TAHD, indicating a potential etiologic association. Comparative metabolic profiling of the MATGs against other Treponema genomes showed a distinct metabolic profile, suggesting potential host adaptation or geographic uniqueness of these newly identified genomospecies. The discovery of novel Treponema genomospecies enhances our understanding of the pathogenesis of pododermatitis and lays the foundation for the development of improved molecular surveillance tools to monitor and manage the disease in free-ranging elk.IMPORTANCETreponema spp. play an important role in the development of pododermatitis in free-ranging elk; however, the species-specific detection of Treponema from pododermatitis lesions is challenging due to culture recalcitrance and limited genomic information. The study utilized shotgun sequencing and in silico genome reconstruction to identify novel Treponema genomospecies from elk with pododermatitis. The discovery of the novel Treponema species opens new avenues to develop molecular diagnostic and epidemiologic tools for the surveillance of pododermatitis in elk. These findings significantly enhance our understanding of the genomic landscape of the Treponemataceae consortium while offering valuable insights into the etiology and pathogenesis of emerging pododermatitis in elk populations.

Shewanella xiamenensis-associated ulcerative dermatitis in koi carp (Cyprinus rubrofuscus).

Ulcerative dermatitis (UD) is common in ornamental fish collections and is typically associated with a wide range of bacterial aetiologies. Clinical reports describing Shewanella xiamenensis-associated UD are limited, however, despite growing attention to pathogenic Shewanella species in fish. Two out of 95 koi carp with UD were presented for clinical assessment by a commercial collection (n = 3000 fish) and subsequently killed on welfare grounds for necropsy. Both specimens exhibited extensive cutaneous ulcers and coelomic fat necrosis with petechial haemorrhages on post-mortem examination. Shewanella xiamenensis was cultured from ulcerated skin tissues taken from both fish, with consistent intralesional gram-negative rod-like bacteria seen on skin scrape cytology. Histology also confirmed intralesional gram-negative rod-like bacteria within multiple ulcerative and erosive dermatitis lesions, plus myofibre necrosis and necrotising coelomic steatitis, in both specimens. Features associated with impaired generalised osmoregulation secondary to UD were detected within the striated muscle underlying the ulcers, the gills, and the caudal aspects of the kidneys. Additional histological features suggestive of sepsis were also seen in one of the fish. In the interim period, morbidity had increased from 3.2% to around 30% of the entire stock. Following culture results, increased pond water changes were implemented (q.2-3d) and the remaining stock was treated with florfenicol, resulting in complete resolution of UD in the collection (as per client). This article highlights the first description of S. xiamenensis-associated UD in koi carp/diseased ornamental fish in the United Kingdom.

Immunological response of lame sheep to clinical interdigital dermatitis and footrot: Procalcitonin, acute phase proteins, and pro-inflammatory cytokines.

In many countries, sheep lameness is a cause of economic concern and a contributing factor to a declining economy. This study aimed to investigate changes in procalcitonin (PCT), acute phase proteins (APPs), and cytokines (CYTs) in response to interdigital dermatitis and footrot in sheep under field conditions, to emphasize their role in the disease pathogenesis, diagnosis, as well as monitoring treatment response. Fifty-three sheep with foot diseases (26 clinical cases with interdigital dermatitis and 27 clinical cases with footrot) and 20 clinically healthy naemi sheep were used in this study. Real time PCR for detection of Fusobacterium necrophorum (F. necrophorum) and Dichelobacter nodosus (D. nodosus) revealed that, all samples collected from lame sheep (N = 53) were positive for D. nodosus (100 %), whereas F. necrophorum was detected in 19 out of 53 samples (35.84 %). The virulent D. nodosus was detected in 48 lameness cases where non-virulent D. nodosus were identified in 5 cases (in concurrent with F. necrophorum). The mean serum levels of PCT, C-reactive protein (CRP), serum amyloid A (SAA), haptoglobin (HP), fibrinogen (Fg) and CYTs (IL1-ß, IL-1α, IFN-γ, IL-6 and TNF-α) in sheep with clinical interdigital dermatitis and footrot were remarkably higher than those detected in control healthy sheep. The serum levels of PCT, CRP, SAA, HP, Fg, and CYTs markers in lame sheep pre- and post-treatment were measured. A substantial decline was detected in serum levels of tested biomarkers of lame sheep after 14 days of treatment. The ROC curves were created. The AUC was assessed to evaluate the accuracy of each variable in distinguishing diseased and healthy sheep. Based on the ROC curves and AUCs; PCT, CRP, SAA, HP, and CYTs were highly diagnostic and predictive for the treatment response of sheep with clinical interdigital dermatitis and footrot. Moreover, all tested biomarkers had a noteworthy role in disease immuno-pathogenesis. Nevertheless, PCT and CRP are better than other tested APPs and CYTs as diagnostic markers for interdigital dermatitis and footrot. However, PCT only has the ability to differentiate sheep with different lameness score.

Immune checkpoint inhibitors unleash pathogenic immune responses against the microbiota.

Immune checkpoint inhibitors (ICIs) are essential components of the cancer therapeutic armamentarium. While ICIs have demonstrated remarkable clinical responses, they can be accompanied by immune-related adverse events (irAEs). These inflammatory side effects are of unclear etiology and impact virtually all organ systems, with the most common being sites colonized by the microbiota such as the skin and gastrointestinal tract. Here, we establish a mouse model of commensal bacteria-driven skin irAEs and demonstrate that immune checkpoint inhibition unleashes commensal-specific inflammatory T cell responses. These aberrant responses were dependent on production of IL-17 by commensal-specific T cells and induced pathology that recapitulated the cutaneous inflammation seen in patients treated with ICIs. Importantly, aberrant T cell responses unleashed by ICIs were sufficient to perpetuate inflammatory memory responses to the microbiota months following the cessation of treatment. Altogether, we have established a mouse model of skin irAEs and reveal that ICIs unleash aberrant immune responses against skin commensals, with long-lasting inflammatory consequences.

Pilot study of dogs with suppurative and non-suppurative Malassezia otitis: A case series.

BACKGROUND: Rarely, Malassezia otitis presents as a painful, erosive otitis with an otic discharge containing Malassezia and neutrophils on cytology. There are no published reports of this type of suppurative Malassezia otitis (SMO). The role of Malassezia hypersensitivity in otitis is still unknown, and no association has been demonstrated with SMO. We compared Malassezia IgE levels, intradermal test and histology changes in SMO dogs with the more conventional Malassezia otitis (MO) presentation. RESULTS: Three dogs (case 1, case 2 and case 3) were diagnosed with SMO, one dog (case 4) was diagnosed with unilateral MO and unilateral SMO, and one dog (case 5) was diagnosed with MO. Only one case (case 4) with SMO/MO had a positive Intradermal Allergy Test (IDAT) and elevated IgE levels for Malassezia. Histopathology findings from SMO revealed: interface dermatitis (case 1 and 3), lymphocytic dermatitis (case 2) and chronic hyperplastic eosinophilic and lymphoplasmacytic dermatitis (case 4). Histopathology findings from MO showed perivascular dermatitis (case 4 and 5). All the cases were treated successfully. CONCLUSIONS: SMO presents with a distinct clinical phenotype in comparison with conventional MO. No consistent aetiology could be isolated. In these clinical cases it is possible that previous treatments could have influenced the results. More research is needed to understand the possible aetiologies and the pathogenesis of SMO.

Microbiota instruct IL-17A-producing innate lymphoid cells to promote skin inflammation in cutaneous leishmaniasis.

Innate lymphoid cells (ILCs) comprise a heterogeneous population of immune cells that maintain barrier function and can initiate a protective or pathological immune response upon infection. Here we show the involvement of IL-17A-producing ILCs in microbiota-driven immunopathology in cutaneous leishmaniasis. IL-17A-producing ILCs were RORγt+ and were enriched in Leishmania major infected skin, and topical colonization with Staphylococcus epidermidis before L. major infection exacerbated the skin inflammatory responses and IL-17A-producing RORγt+ ILC accumulation without impacting type 1 immune responses. IL-17A responses in ILCs were directed by Batf3 dependent CD103+ dendritic cells and IL-23. Moreover, experiments using Rag1-/- mice established that IL-17A+ ILCs were sufficient in driving the inflammatory responses as depletion of ILCs or neutralization of IL-17A diminished the microbiota mediated immunopathology. Taken together, this study indicates that the skin microbiota promotes RORγt+ IL-17A-producing ILCs, which augment the skin inflammation in cutaneous leishmaniasis.

A novel mutation in early-onset sarcoidosis/Blau syndrome: an association with Propionibacterium acnes.

BACKGROUND: Early-onset sarcoidosis (EOS) and Blau syndrome (BS) are systemic inflammatory granulomatous diseases without visible pulmonary involvement, and are distinguishable from their sporadic and familial forms. The diseases are characterized by a triad of skin rashes, symmetrical polyarthritis, and recurrent uveitis. The most common morbidity is ocular involvement, which is usually refractory to conventional treatment. A gain-of-function mutation in the nucleotide-binding oligomerization domain-containing protein 2 (NOD2) gene has been demonstrated in this disease; however, little is known about the relationship between the activation of NOD2 and the pathophysiology of EOS/BS. Here we describe EOS/BS with a novel mutation in the NOD2 gene, as well as detection of Propionibacterium acnes (P. acnes) in the granulomatous inflammation. CASE PRESENTATION: An 8-year-old Japanese girl presented with refractory bilateral granulomatous panuveitis. Although no joint involvement was evident, she exhibited skin lesions on her legs; a skin biopsy revealed granulomatous dermatitis, and P. acnes was detected within the sarcoid granulomas by immunohistochemistry with P. acnes-specific monoclonal (PAB) antibody. Genetic analyses revealed that the patient had a NOD2 heterozygous D512V mutation that was novel and not present in either of her parents. The mutant NOD2 showed a similar activation pattern to EOS/BS, thus confirming her diagnosis. After starting oral prednisolone treatment, she experienced an anterior vitreous opacity relapse despite gradual prednisolone tapering; oral methotrexate was subsequently administered, and the patient responded positively. CONCLUSIONS: We presented a case of EOS/BS with a novel D512V mutation in the NOD2 gene. In refractory granulomatous panuveitis cases without any joint involvement, EOS/BS should be considered as a differential diagnosis; genetic analyses would lead to a definite diagnosis. Moreover, this is the first report of P. acnes demonstrated in granulomas of EOS/BS. Since intracellular P. acnes activates nuclear factor-kappa B in a NOD2-dependent manner, we hypothesized that the mechanism of granuloma formation in EOS/BS may be the result of NOD2 activity in the presence of the ligand muramyl dipeptide, which is a component of P. acnes. These results indicate that recognition of P. acnes through mutant NOD2 is the etiology in this patient with EOS/BS.

Non-tuberculous Mycobacterial Granulomatous Dermatitis in an African Pygmy Hedgehog (Atelerix albiventris).

A 2-year-old female African pygmy hedgehog (Atelerix albiventris) with a cutaneous nodular lesion on the dorsal surface of the right forelimb was presented for clinical examination. Histopathological findings included granulomatous dermatitis with extensive necrosis. Long and slender acid-fast bacilli were seen within the cytoplasm of macrophages and in extracellular spaces. Bacteriological culture of skin revealed acid-fast bacilli and non-tuberculous mycobacterial infection was confirmed by gene sequencing and identity analysis using the BLAST tool. To our knowledge, this is the first report of non-tuberculous granulomatous dermatitis in hedgehogs.

A shotgun metagenomic investigation of the microbiota of udder cleft dermatitis in comparison to healthy skin in dairy cows.

Udder cleft dermatitis (UCD) is a skin condition affecting the fore udder attachment of dairy cows. UCD may be defined as mild (eczematous skin changes) or severe (open wounds, large skin changes). Our aims were to compare the microbiota of mild and severe UCD lesions with the microbiota of healthy skin from the fore udder attachment of control cows, and to investigate whether mastitis-causing pathogens are present in UCD lesions. Samples were obtained from cows in six dairy herds. In total, 36 UCD samples categorized as mild (n = 17) or severe (n = 19) and 13 control samples were sequenced using a shotgun metagenomic approach and the reads were taxonomically classified based on their k-mer content. The Wilcoxon rank sum test was used to compare the abundance of different taxa between different sample types, as well as to compare the bacterial diversity between samples. A high proportion of bacteria was seen in all samples. Control samples had a higher proportion of archaeal reads, whereas most samples had low proportions of fungi, protozoa and viruses. The bacterial microbiota differed between controls and mild and severe UCD samples in both composition and diversity. Subgroups of UCD samples were visible, characterized by increased proportion of one or a few bacterial genera or species, e.g. Corynebacterium, Staphylococcus, Brevibacterium luteolum, Trueperella pyogenes and Fusobacterium necrophorum. Bifidobacterium spp. were more common in controls compared to UCD samples. The bacterial diversity was higher in controls compared to UCD samples. Bacteria commonly associated with mastitis were uncommon. In conclusion, a dysbiosis of the microbiota of mild and severe UCD samples was seen, characterized by decreased diversity and an increased proportion of certain bacteria. There was no evidence of a specific pathogen causing UCD or that UCD lesions are important reservoirs for mastitis-causing bacteria.

Activation of aryl hydrocarbon receptor in Langerhans cells by a microbial metabolite of tryptophan negatively regulates skin inflammation.

BACKGROUND: Skin commensal bacteria play important roles in skin homeostasis. Langerhans cells (LCs) are epidermis-resident dendritic cells that sense environmental stimuli and are critical in the induction of immune tolerance to allergen and bacterial skin flora. However, response of LCs to the metabolites of the skin microbiota is not clear. OBJECTIVE: To explore the effects of the skin microbial metabolites on LCs activation. METHODS: LCs derived from CD34+ hematopoietic stem cells in the cord blood were treated with a microbial metabolite of tryptophan, indole-3-aldehyde (IAId). Activation aryl hydrocarbon receptor (AhR) signaling, production of IL-10, and expression of receptor activator of NF-κB (RANK) / receptor activator of NF-κB ligand (RANKL) in LCs or keratinocytes were analyzed using quantitative PCR, western blotting and flow cytometry. LCs maturation induced by IAId and CD4+ T cell response induced by IAId-conditioned LCs were also investigated. RESULTS: IAId induced the production of indoleamine 2,3-dioxygenase (IDO) and IL-10 in LCs through the activation of AhR. IAId promoted the expression of RANK and RANKL on LCs and keratinocytes in an AhR-dependent manner respectively, which might result in activation of NF-κB signaling and production of IL-10. Moreover, a mature phenotype of LCs was induced by IAId, and IAId-activated LCs inhibited CD4+ T cell proliferation and induced IL-10 secretion. CONCLUSIONS: Our study revealed a negatively regulatory function of a tryptophan metabolite on LCs through the activation of AhR, and the microbial metabolites could be utilized in future treatment for inflammatory skin diseases.

Orbital abscess caused by Exophiala dermatitidis following posterior subtenon injection of triamcinolone acetonide: a case report and a review of literature related to Exophiala eye infections.

BACKGROUND: Subtenon injection of triamcinolone acetonide (STTA) has been widely adopted in the clinical setting of ophthalmology and its infectious complications are rare. However, orbital abscess following STTA has been reported in seven cases. Furthermore, although eye infections due to Exophiala species are uncommon, there have been 19 cases to date. E. jeanselmei, E. phaeomuriformis, E. werneckii, and E. dermatitidis have been reported to cause human eye infections; however, to the best of our knowledge, orbital abscess caused by E. dermatitidis has not yet been reported. We describe the first documented case of fungal orbital abscess caused by E. dermatitidis following STTA. We also review the related literature of orbital abscess following STTA, as well as eye infections caused by the four Exophiala species. CASE PRESENTATION: The patient was a 69-year-old Japanese woman with diabetic mellitus. She had a macular oedema in her right eye, which occurred secondary to branch retinal vein occlusion. An orbital abscess caused by E. dermatitidis occurred 4 months after the second STTA for the macular oedema, which was successfully treated by a surgical debridement and systemic administration of voriconazole. CONCLUSIONS: Our findings in the patient and from our literature survey caution ophthalmologists to the fact that STTA can cause fungal orbital infections, especially in diabetic patients. Furthermore, surgical treatment is one of the most important risk factors.

Persistent Corynebacterium bovis Infectious Hyperkeratotic Dermatitis in Immunocompetent Epidermal-Mutant dep/dep Mice.

During a previously reported program-wide Corynebacterium bovis outbreak, both immunocompetent depilated (dep/dep) mutant mice and transgenic mice that express the papillomavirus E6 oncoprotein became persistently infected with C. bovis. An orthokeratotic, hyperkeratotic, acanthotic dermatitis developed in the C. bovis-infected dep/dep mice, which remained C. bovis PCR-positive for >45 days prior to euthanasia as part of the program-wide C. bovis eradication effort. Since both affected strains of mice have altered skin homeostasis, immune status or the presence of hair may not alone be sufficient to explain strain susceptibility to C. bovis-related cutaneous disease. In order to avoid invalidation of preclinical studies due to C. bovis infection, it may be necessary to isolate immunodeficient mouse strains, implement facililty-wide surveillance for C. bovis, and sterilize equipment with vaporized hydrogen peroxide.

Epidemiological analysis of Arcanobacterium phocae isolated from cases of mink dermatitis of a single farm.

The present study was designed to identify nine Arcanobacterium phocae strains isolated from cases of mink dermatitis of a single farm in Finland and characterize the strains for epidemiological relationships. All nine strains and previously described A. phocae used for comparative purposes were identified and further characterized phenotypically, by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), by Fourier Transform Infrared Spectroscopy (FT-IR) and genotypically by detection of phocaelysin encoding gene phl with a previously developed loop-mediated isothermal amplification (LAMP) assay and by sequencing 16S rRNA gene and gene phl, the elongation factor tu encoding gene tuf and the ß subunit of bacterial RNA polymerase encoding gene rpoB. Genetic relatedness among isolates was determined using whole-genome single nucleotide polymorphism (wgSNP) analysis. The wgSNP results, partly the MALDI-TOF MS and FT-IR analyses and sequencing of the genes, revealed that the nine A. phocae strains recovered from a single farm showed close sequence similarities among each other and differed from previously investigated A. phocae strains isolated from other farms and animals in Finland and from the A. phocae type strain. This indicated a close epidemiological relationship of the A. phocae strains isolated from a single farm and that the nine A. phocae strains of the present study might have developed from a common ancestor.

Malassezia Yeasts in Veterinary Dermatology: An Updated Overview.

Lipophilic yeasts of the genus Malassezia are important skin commensals and opportunistic skin pathogens in a variety of animals. The species M. pachydermatis was first isolated from the skin of a captive Indian rhinoceros with an exfoliative dermatitis in 1925, recognized as an important otic pathogen of dogs in the 1950's, and finally accepted, after several years of controversy, as a common cause of canine dermatitis in the 1990's. Since then, there has been considerable research into the biology of Malassezia yeasts and their interaction with their animal hosts. In dogs and cats, M. pachydermatis is associated with ceruminous otitis externa and a "seborrhoeic" dermatitis, wherein pruritic, erythematous skin lesions, often with brown/black greasy, malodourous material matting hairs, preferentially develop in intertriginous areas. Skin disease is favored by folds, underlying hypersensitivity disorders, endocrinopathies, defects of cornification, and in cats, various visceral paraneoplastic syndromes. Diagnosis is based on detecting the yeast in compatible skin lesions, usually by cytology, and observing a clinical and mycological response to therapy. Treatment normally comprises topical or systemic azole therapy, often with miconazole-chlorhexidine shampoos or oral itraconazole or ketoconazole. Management of concurrent diseases is important to minimize relapses. Historically, wild-type Malassezia isolates from dogs and cats were typically susceptible to azoles, with the exception of fluconazole, but emerging azole resistance in field strains has recently been associated with either mutations or quadruplication of the ERG11 gene. These observations have prompted increased interest in alternative topical antifungal drugs, such as chlorhexidine, and various essential oils. Further clinical trials are awaited with interest.