Is milbemycin a game changer against antifungal drug-resistant mycoses?

Milbemycin oximes are macrocyclic lactones that have a broad spectrum of activity against nematode infection in animals. They are known to block drug efflux, which increases the susceptibility of fungi to azoles. We investigated the effects of milbemycin on the azole susceptibility of fungi (Aspergillus fumigatus, Candida albicans, C. auris, Cryptococcus neoformans, and Trichophyton rubrum). To screen for changes in azole susceptibility, fungal growth was tested on a culture medium containing 1 µg/ml milbemycin. The results showed that milbemycin increased the azole susceptibility of azole-resistant strains of C. albicans, C. auris, C. neoformans, and T. rubrum. Thus, milbemycin might be useful against antifungal drug-resistant strains.

Milbemycin blocks drug efflux and increases the azole susceptibility of azole-resistant strains of Candida albicans, C. auris, Cryptococcus neoformans, and Trichophyton rubrum. This drug is expected to be a game changer against antifungal drug-resistant infections.

Evaluation of the association between osteoporotic vertebral compression fractures and psoas major/paraspinal muscle mass and ADC measured on MRI.

OBJECTIVE: Evaluate magnetic resonance imaging factors associated with osteoporotic vertebral compression fractures. MATERIALS AND METHODS: We retrospectively reviewed 457 patients' records. Age, sex, and body mass index were recorded. Two blinded readers measured psoas major and paraspinal muscle areas at the L3 vertebral body level on transverse T2-weighted magnetic resonance images and the mean apparent diffusion coefficient values of the non-fractured vertebrae from Th12 to L5. Inter-reader reliability for continuous variables was assessed by intraclass correlation coefficients. RESULTS: We evaluated 210 patients (103 [49.0%] men). The osteoporotic vertebral compression fractures group was older and had lower BMI and smaller psoas major and paraspinal muscle areas than the group without vertebral compression fractures (p < 0.001). The mean apparent diffusion coefficient was weakly correlated with paraspinal muscle area in the osteoporotic vertebral compression fractures group. The intraclass correlation coefficient value was 0.83, and the intraclass correlation coefficients of the psoas major and paraspinal muscles were 0.94 and 0.97, respectively. Multivariate analysis revealed that decreased psoas major and paraspinal muscle areas and increased mean apparent diffusion coefficient values were significantly associated with the presence of osteoporotic vertebral compression fractures (all p < 0.05). Psoas major and paraspinal muscle areas showed relatively high predictive accuracy (57%, 61%). CONCLUSION: Psoas major and paraspinal muscle areas at the L3 level and the mean apparent diffusion coefficient value of non-fractured vertebrae from the Th12 to L5 level were associated with osteoporotic vertebral compression fractures. This may contribute to detecting the potential risk of healthy individuals developing osteoporotic vertebral compression fractures.

Optimal threshold score of aortic valve calcification for identification of significant aortic stenosis on non-electrocardiographic-gated computed tomography.

OBJECTIVES: This study evaluated the association between aortic valve calcification (AVC) and aortic stenosis (AS) by scoring the AVC to determine the threshold scores for significant AS on non-electrocardiographic (ECG)-gated computed tomography (CT). METHODS: We retrospectively analyzed the AVC scores of 5385 patients on non-contrast non-ECG-gated CT, who underwent transthoracic echocardiography (TTE) from March 1, 2013, to December 26, 2019, at our institution. Multivariable logistic regression models were used to identify potential risk factors for significant AS. The thresholds for significant AS were computed using receiver operator characteristic (ROC) curves, based on the AVC scores after propensity score matching. RESULTS: A significant association was found between AS and age (p < 0.001; odds ratio [OR], 1.04; 95% confidence interval [CI], 1.02-1.06), female sex (p < 0.001; OR, 4.5; 95% CI, 2.75-7.36), bicuspid aortic valve (p < 0.001; OR, 23.2; 95% CI, 7.35-72.9), and AVC score (AVC score/100) (p < 0.001; OR, 1.82; 95% CI, 1.71-1.95). All sex-specific AVC thresholds for significant AS (moderate and over AS severity, moderate and over AS severity without discordance, discordant severe AS, and concordant severe AS) showed high sensitivity and specificity (AUC, 0.939-0.968; sensitivity, 84.6-96%; specificity, 84.2-97.1%). CONCLUSIONS: We determined the optimal AVC threshold scores for significant AS, which may aid in diagnosing significant asymptomatic AS on incidental detection of AVC through non-ECG-gated CT for non-cardiac indications. KEY POINTS: • Increased frequency of non-electrocardiographic (ECG)-gated computed tomography (CT) for non-cardiac indications has led to the increased incidental identification of aortic valve calcification (AVC). • It is important to identify patients with significant aortic stenosis (AS) who require additional echocardiographic assessment on incidental detection of AVC via non-ECG-gated CT. • We determined the AVC thresholds with high sensitivity and specificity to identify significant AS on non-ECG-gated CT, which could lead to early diagnosis of asymptomatic significant AS and improved prognosis.

Genomic Analysis of Antifungal Drug Resistance Induced in Trichophyton rubrum After Prolonged Culture with Terbinafine.

In this study, we induced terbinafine (TRF) resistance in a T. rubrum strain in vitro for 18 months then compared the genomes of the TRF-resistant (N42-3) and TRF-susceptible wild-type (N42WT) strains to identify mutations. In the SQLE gene, N42WT had no mutation while N42-3 had a F397L mutation. We sequenced approximately 22.53 Mb of the genomes of the N43WT and N42-3 strains. Other than the F397L mutation in SQLE, there were three other genetic mutations in three different genes that were found in N42-3, but not in N43WT; however, these three mutations were not detected in other TRF-resistant T. rubrum strains. From this genome sequencing analysis, the only variation that was confirmed to be associated with drug resistance in the genome of the TRF-resistant T. rubrum was a hotspot mutation in SQLE.

Long Amplification PCR (LA-PCR) Detection of Azole Resistant Trichophyton indotineae.

Trichphyton indotineae, a species newly designated in 2020 independent of T. interdigitale, comprises highly terbinafine (TRF)-resistant dermatophytosis that is epidemic in North India and spreding to worldwide. Some clinical isolates of T. indotineae have been resistance both TRF and azoles that might be caused the treatment failure. To detect the azole resistance strains, we developed a long amplification PCR (LA-PCR) detection method for the tandem repeat of the CYP51B (encoding sterol 14a-demethylase gene) in T. indotineae. Contrasting the drug susceptibility test results with the LA-PCR results confirmed a trend toward low susceptibility to azole antifungal agents in strains with amplifications of 9.5 kbp or greater (3 or more copies of CYP51B). Our results suggest that the method could be detected rapidly of low-susceptibility strains to azole antifungal agents.

Internal Transcribed Spacer Region Typing of Trichophyton interdigitale Isolated from Japanese Patients.

Trichophyton interdigitale, an anthropophilic species, is one of the main causative agents of tinea unguium and tinea pedis. T. interdigitale and the zoophilic species T. mentagrophytes are morphologically and physiologically very similar. Isolates of the T. interdigitale/T. mentagrophytes complex from around the world have been classified into more than 10 internal transcribed spacer (ITS) genotypes. In this study, we isolated T. interdigitale from Japanese patients and investigated which ITS type was more common. The ITS regions of 29 clinical isolates of T. interdigitale and one clinical isolate of T. mentagrophytes were sequenced. The phylogenetic analysis of the ITS region sequences revealed that the 29 isolates of T. interdigitale belong to ITS type II of T. interdigitale. The one clinical isolate of T. mentagrophytes was in the same cluster with ITS type II* of T. mentagrophytes. One terbinafine-resistant strain of T. interdigitale also belonged to ITS type II of T. interdigitale.

Clinical Isolate of a Multi-Antifungal-Resistant Trichophyton rubrum.

The multi-antifungal drug-resistant strain (NUBS21012) of Trichophyton rubrum was isolated from a patient with recurrent tinea corporis. The resistant strain encoded Phe at codon 393 instead of Leu (L393F) in the squalene epoxidase (SQLE) gene. The expression of genes encoding ATP-binding cassette transporter proteins increased in the strain compared to that of other strains. This result provides evidence that ATP-binding cassette transporter proteins are closely associated with azole resistance.

Preoperative prediction for mastoid extension of middle ear cholesteatoma using temporal subtraction serial HRCT studies.

OBJECTIVES: This study investigated the utility of temporal subtraction computed tomography (TSCT) obtained with temporal bone high-resolution computed tomography (HRCT) for the preoperative prediction of mastoid extension of middle ear cholesteatomas. METHODS: Twenty-eight consecutive patients with surgically proven middle ear cholesteatomas were retrospectively evaluated. The presence of black color in the mastoid region on TSCT suggested progressive changes caused by bone erosion. Enlarged width of the anterior part of mastoid on HRCT was interpreted as suggestive of mastoid extension. Fisher's exact test was used to compare the widths and black color on TSCT for cases with and without mastoid extension. The diagnostic accuracy of TSCT and HRCT for detecting mastoid extension and interobserver agreement during the evaluation of black color on TSCT were calculated. RESULTS: There were 15 cases of surgically proven mastoid extension and 13 cases without mastoid extension. Patients with black color on TSCT were significantly more likely to have a mastoid extension (p < 0.001). The sensitivity and specificity of TSCT were 0.93 and 1.00, respectively. Patients in whom the width of the anterior part of the mastoid was enlarged were significantly more likely to have a mastoid extension (p = 0.007). The sensitivity and specificity of HRCT to detect the width of the anterior part of the mastoid were 0.80 and 0.77, respectively. Interobserver agreement during the evaluation of TSCT findings was good (k = 0.71). CONCLUSIONS: This novel TSCT technique and preoperative evaluations are useful for assessing mastoid extension of middle ear cholesteatomas and making treatment decisions. KEY POINTS: •TSCT shows a clear black color in the mastoid region when the middle ear cholesteatoma is accompanied by mastoid extension. •TSCT obtained with preoperative serial HRCT of the temporal bone is useful for assessing mastoid extension of middle ear cholesteatomas.

A deletion mutation in the amino acid sequence of squalene epoxidase in terbinafine-resistant Trichophytonrubrum.

INTRODUCTION: Trichophyton rubrum is an anthropophilic dermatophyte that is most frequently isolated from onychomycosis (tinea unguium) worldwide. T. rubrum strains showing resistance to the anti-fungal drug terbinafine (TRF) have also been isolated from human patients worldwide. METHODS: In this study, we isolated a TRF-resistant strain (N99-2) of T. rubrum from a patient with recurrent tinea unguium. In vitro susceptibility of the clinical isolate to TRF, itraconazole (ITZ), ravuconazole (RVZ), and luliconazole (LCZ) was investigated using the Clinical & Laboratory Standards Institute M38-A2 test. To identify mutations, we compared the gene sequence of N99-2 to that of a TRF-susceptible strain of T. rubrum. Results; In N99-2, the minimum inhibitory concentrations were 32 mg/L for TRF, <0.03 mg/L for ITZ, <0.03 mg/L for RVZ, and <0.03 mg/L for LCZ. The squalene epoxidase (SQLE) gene sequence in N99-2 was determined to be 1467 bp in length, and it encoded a protein of 488 amino acids, beginning with a putative initiating methionine (ATG). The following mutations were identified from the SQLE of N99-2: L393F and Y394del. CONCLUSIONS: This is the first report of the detection of a deletion mutation in SQLE in a TRF-resistant strain. The protein of SQLE is the target of TRF, and it is essential for cell membrane synthesis in dermatophytes. However, dermatophyte cells were found to undergo gene mutations to escape the effects of antifungal agents.

Hemorrhagic Complication in Surgical Resection for Massive Plexiform Neurofibroma in Body Trunk: The Flow-Void Sign as a Predictor and Preoperative Embolization as Prevention.

BACKGROUND: Plexiform neurofibromas (PNs) are highly vascularized and potentially malignant tumors. Surgical resection of a PN can be complicated by perioperative hemorrhagic events (PHE), including excessive intraoperative blood loss and postoperative hematoma at the surgical site. This study aimed to evaluate the predictive factors of PHE and the usefulness of preoperative embolization for PN. MATERIALS AND METHODS: Consecutive surgical resections of 24 massive PNs in the body trunk with a maximum diameter > 5 cm in 22 patients between January 2015 and December 2020 were reviewed. Patient demographics, laboratory analyses, MRI findings, preoperative transcatheter arterial embolization (TAE), and pathological findings were evaluated between PNs with and without PHE, which consists of intraoperative blood loss over 15% of their estimated total blood volume and/or postoperative hematoma requiring surgical intervention or blood transfusion. RESULTS: PHE was observed in 7 out of 24 PNs (29.2%), with 5 events of excessive intraoperative bleeding and 2 postoperative hematomas. The PHE group (n = 7) showed a significantly higher flow-void effect inside the tumor on preoperative MRI than the non-PHE group (n = 17) (P = 0.0186). Preoperative TAE was not associated with PHE occurrence for the 24 PNs; however, it significantly reduced the PHE risk by 12 PNs with a flow-void sign (P = 0.00126). Other characteristics showed no significant differences between groups. CONCLUSION: The flow-void sign on MRI can be the only predictive factor of PHE in surgical resection for massive PNs in the body trunk. Preoperative TAE can reduce the PHE risk for PNs with a flow-void sign.

Quantitative Histogram Analysis of T2-Weighted and Diffusion-Weighted Magnetic Resonance Images for Prediction of Malignant Thymic Epithelial Tumors.

PURPOSE: To assess the value of histogram analysis for differentiating a high-risk thymic epithelial tumor (TET) from a low-risk TET using T2-weighted images and the apparent diffusion coefficient (ADC). METHODS: Forty-nine patients with histopathologically proven TET after thymectomy were enrolled in this study and retrospectively classified as having low-risk TET (low-risk thymoma) or high-risk TET (high-risk thymoma or thymic carcinoma). Twelve parameters were obtained from the quantitative histogram analysis. The histogram parameters were compared using the Mann-Whitney U test. Diagnostic efficacy was estimated by receiver-operating characteristic curve analysis. RESULTS: Twenty-five patients were classified as having low-risk TET and 24 as having high-risk TET. The mean ADC value showed diagnostic efficacy for differentiating high-risk TET from low-risk TET, with an area under the curve of 0.7, and was better than when using conventional methods alone. CONCLUSION: The ADC-based histogram analysis could help to differentiate between high-risk and low-risk TETs.

The Clonal Population of Trichophyton equinum from Dermatophytoses of Japanese Racehorses.

Trichophyton equinum is a zoophilic dermatophyte that is frequently isolated from horse dermatophytosis and rare infections in humans. In the present study, molecular and physiological testing were performed on T. equinum isolates from dermatophytoses of Japanese racehorses to assess genotype and phenotype patterns of these strains. Comparative nucleotide sequence analysis showed that internal transcribed spacer (ITS) region sequences amplified from all Japanese isolates were 99.5% identical to T. equinum reference strains. ITS sequences amplified among the isolates were 100% (BT2) showed that isolates were 100% identical and harbored a "T" single nucleotide polymorphism at position 18. The sequences of ß-tubulin (BT2) showed that isolates were 100% identical to T. equinum reference strains. The MAT1-2 allele was detected by PCR in all seven isolates, whereas none of the isolates contained the MAT1-1 allele. All isolates grew only on Trichophyton Agar 5 and did not grow on Trichophyton Agar 1 and 4, indicating nicotinic acid requirement. These results suggest that Japanese T. equinum isolates are derived from a clonal population.

Protothecosis in Dogs and Cats-New Research Directions.

Protothecosis refers to disease of humans and animals caused by infection with fungus-like, colourless microalgae of the genus Prototheca. Although protothecosis remains an uncommon infection, increasing numbers of human and animal cases are being diagnosed worldwide. This review summarises major new findings in basic science (sequencing analyses of sterol 14α-demethylase (CYP51/ERG11) genes and organelle genomes of Prototheca wickerhamii) to elucidate taxonomic features of this pathogen. Furthermore, this review updates and summarises the clinical features, diagnosis and treatment of protothecosis in dogs and cats. This content of this review is based on information presented at the medical phycology symposium held in the 20th Congress of the International Society for Human and Animal Mycology ( https://www.isham.org/ ).

Antifungal susceptibility of dermatophytes from racehorses in Japan.

BACKGROUND: Luliconazole (LCZ) is an imidazole antifungal medication that exhibits excellent activity against dermatophytes. As a topical cream and lotion (approved for human use), LCZ has demonstrated a broad spectrum of activity against human dermatophytoses. OBJECTIVES: This is the first study to investigate the in vitro susceptibility of clinical isolates from horse dermatophytoses to LCZ. ANIMALS: No animals were used in this study. METHODS AND MATERIALS: In the present study, the in vitro susceptibilities of clinical isolates of dermatophytes to LCZ, clotrimazole (CTZ), miconazole (MCZ) and terbinafine (TRF) were investigated using the Clinical & Laboratory Standards Institute M38-A2 test. RESULTS: The minimum inhibitory concentrations (MICs) for all 16 clinical isolates of Trichophyton equinum, Microsporum equinum/canis and M. gypseum for LCZ were <0.03 mg/L. The MICs of all isolates were <0.03-0.5 mg/L for CTZ, 0.03-16 mg/L for MCZ and <0.03-1 mg/L for TRF. CONCLUSIONS: LCZ demonstrated a broad spectrum of activity against clinical isolates from horse dermatophytoses. We consider that LCZ will become the primary antifungal agent for treating horse dermatophytosis.

In vitro algaecid effect of itraconazole and ravuconazole on Prototheca species.

Protothecosis is a rare infection in humans, dogs, and cats, and its causative agent is Prototheca species, which consists of achlorophyllic algae that are ubiquitous in natural environments and hosts intestinal flora. Ravuconazole (RVZ) is a new available human azole drug in Japan since 2018 and broad-spectrum antifungal agent. In the present study, the in vitro susceptibility of clinical and environmental isolates of P. wickerhamii, P. zopfii, and P. blaschkeae to itraconazole (ITZ) voriconazole (VRZ), posaconazole (PCZ), and RVZ. RVZ was more potent than the other azoles against Protheca species and has considerable potential for use as a therapeutic agent for human and animal protothecosis.

High multi-azole-resistant Malassezia pachydermatis clinical isolates from canine Malassezia dermatitis.

Malassezia pachydermatis, a lipophilic and aerobic yeast, is a causative agent of Malassezia dermatitis, a common skin mycosis in dogs and cats. This fungus is also responsible for zoonotic fungal infections in human neonates. Ravuconazole (RVZ) is an antifungal azole compound and the active metabolite of fosravuconazole, which was approved for use in humans in Japan in 2018. In the present study, in vitro RVZ susceptibility and multi-azole resistance of 13 clinical M. pachydermatis strains was investigated using the modified Clinical and Laboratory Standards Institute M27-A3 test. The minimum inhibitory concentrations (MICs) for the 13 isolates ranged from 0.094 to >32 mg/L for itraconazole (ITZ) and from 0.5 to >32 mg/l for RVZ. Similarly, MICs for ITZ- or RVZ-resistant strains (MICs >32 mg/l) were also >32 mg/l for clotrimazole (CTZ), >32 mg/l for miconazole (MCZ), and 0.25 to >32 mg/L for voriconazole (VRZ). BLAST analysis using the NCBI database showed that ERG11 cDNA of the RVZ-resistant strain encoded Gly at codon 461 and Asp in cytochrome p450 encoded by M. pachydermatis ERG11 mRNA. This work is the first report to describe that an RVZ-resistant M. pachydermatis strain contains ERG11 mutations. The affinity of the protein encoded by ERG11 for RVZ may differ from that of ITZ. Therefore, RVZ has considerable therapeutic potential for treating ITZ-resistant canine Malassezia dermatitis. However, RVZ-resistant strains already exist in canine Malassezia dermatitis in Japan.

Emergence of Fungal-Like Organisms: Prototheca.

The genus Prototheca consists of achlorophyllic algae that are ubiquitous in the environment and animal intestines. However, this organism has forfeited its photosynthetic ability and switched to parasitism. In 1894, Krüger described two microorganisms isolated in Germany from mucous flux of Tilia and Ulmus spp., namely Prototheca moriformis and P. zopfii. Based on their yeast-like colony morphology, Krüger classified these organisms as fungi. The genus is now included within the class Trebouxiophyceae, order Chlorellales, and family Chlorellaceae. Historically, protothecosis and infections caused by green algae have been studied in the field of medical mycology. Prototheca spp. have been found to colonize human skin, fingernails, the respiratory tract, and digestive system. Although human infection by Prototheca is considered rare, an increase in infections has been noted among immunosuppressed patients, those on corticosteroid treatment, or both. Moreover, the first human outbreak of protothecal algaemia and sepsis was recently reported in a tertiary care chemotherapy oncology unit in 2018. Prototheca is also a causative pathogen of bovine disease. Prototheca zopfii and P. blaschkeae are associated with bovine mastitis, which causes a reduction in milk production and secretion of thin, watery milk containing white flakes. Economic losses are incurred either directly via reduced milk production and premature culling of affected animals or indirectly as a result of treatment and veterinary care expenses. Thus, knowledge of this fungal-like pathogen is essential in human and veterinary medicine. In this mini-review, I briefly introduce human and animal protothecoses.

Trichophyton indotineae sp. nov.: A New Highly Terbinafine-Resistant Anthropophilic Dermatophyte Species.

In this report, we describe the first isolation of two highly terbinafine (TRF)-resistant Trichophyton interdigitale-like strains from a Nepali patient and an Indian patient with tinea corporis in Japan. These strains (designated NUBS19006 and NUBS19007) exhibited a TRF minimal inhibitory concentration (MIC) of > 32 mg/L and contained a missense mutation (Phe397Leu) in squalene epoxidase (SQLE) gene. The internal transcribed spacer (ITS) region sequences amplified from the isolates (NUBS19006 and NUBS19007) were 99.5% identical to Japanese isolates of T. interdigitale and T. interdigitale strain CBS 428.63. The homology of region sequences were also 97.6% identical to T. mentagrophytes strain CBS 318.56. Moreover, the ITS sequences amplified from the isolates were 100% identical to highly TRF-resistant strains of T. interdigitale, which were isolated in Delhi, India, and harbored mutations in SQLE. The urease test on Christensen's urease agar was positive for T. mentagrophytes and T. interdigitale after 7 days of incubation. On the other hand, the type strain of T. rubrum CBS 100081 T and highly TRF-resistant strains (NUBS19006 and NUBS19007) were negative on Christensen urease agar after 7 and 14 days of incubation. Moreover, NUBS19006 and NUBS19007 were also negative reaction on the hair perforation test. To avoid confusion in the taxonomy of the T. mentagrophytes/T. interdigitale complex, we suggest that the highly TRF-resistant Indian strains be considered a new species independent of T. interdigitale, according to clinical and mycological features.

Miconazole-tolerant strains of Malassezia pachydermatis generated by culture in medium containing miconazole.

BACKGROUND: Tolerance of Malassezia pachydermatis to azole drugs has been reported worldwide, from strains isolated from dogs. Canine Malassezia dermatitis often is treated with shampoos containing 2% miconazole (MCZ) or other topical MCZ products. OBJECTIVES: In the in vitro study herein, it was investigated whether MCZ-induced amino acid substitutions in the lanosterol 14-alpha-demethylase (ERG11) gene 1 lead to azole tolerance in M. pachydermatis. METHODS AND MATERIALS: Toleranced to MCZ was induced in an azole-susceptible strain of M. pachydermatis (CBS1879T ) by culture in medium containing MCZ. Antifungal susceptibility to MCZ, clotrimazole (CTZ) and itraconazole (ITZ) was assessed using the modified broth microdilution (BM) method. To assess the potential mechanism of tolerance in the three MCZ-resistant strains, ERG11 was sequenced. The interaction between the calcineurin inhibitor tacrolimus and MCZ in the azole-tolerant isolates also was examined. RESULTS: Three strains (NUBS19001 to NUBS19003) from CBS1879T cultured in medium containing MCZ exhibited minimum inhibitory concentrations (MICs) of 40 mg/L to MCZ, 5 mg/L to ITZ and >32 mg/L to CTZ, meaning that the isolates were tolerant. The combination of MCZ and tacrolimus exerted an indifferent effect against the MCZ-tolerant strain. BLAST analysis using the NCBI database showed mutations in the cytochrome p450 encoded by ERG11 in the MCZ-tolerant strains. CONCLUSIONS: In the present in vitro study, it was shown that MCZ exposure can induce amino acid substitutions in ERG11 and subsequent tolerance of M. pachydermatis to several azoles. Whether topical therapy with azole-containing products can exert a similar effect in vivo is a question that requires further research.

Biology, diagnosis and treatment of Malassezia dermatitis in dogs and cats Clinical Consensus Guidelines of the World Association for Veterinary Dermatology.

BACKGROUND: The genus Malassezia is comprised of a group of lipophilic yeasts that have evolved as skin commensals and opportunistic cutaneous pathogens of a variety of mammals and birds. OBJECTIVES: The objective of this document is to provide the veterinary community and other interested parties with current information on the ecology, pathophysiology, diagnosis, treatment and prevention of skin diseases associated with Malassezia yeasts in dogs and cats. METHODS AND MATERIAL: The authors served as a Guideline Panel (GP) and reviewed the literature available prior to October 2018. The GP prepared a detailed literature review and made recommendations on selected topics. The World Association of Veterinary Dermatology (WAVD) Clinical Consensus Guideline committee provided guidance and oversight for this process. The document was presented at two international meetings of veterinary dermatology societies and one international mycology workshop; it was made available for comment on the WAVD website for a period of six months. Comments were shared with the GP electronically and responses incorporated into the final document. CONCLUSIONS AND CLINICAL IMPORTANCE: There has been a remarkable expansion of knowledge on Malassezia yeasts and their role in animal disease, particularly since the early 1990's. Malassezia dermatitis in dogs and cats has evolved from a disease of obscurity and controversy on its existence, to now being a routine diagnosis in general veterinary practice. Clinical signs are well recognised and diagnostic approaches are well developed. A range of topical and systemic therapies is known to be effective, especially when predisposing factors are identified and corrected.