Malassezia yeasts, common skin commensals in warm-blooded vertebrates, play a significant role in the cutaneous ecology of animals, particularly dogs and cats. These yeasts rely on lipids for growth, a trait attributed to the loss of fatty acid synthetase genes, making them closely associated with animal hosts. Environmental factors like heat and humidity, along with changes in host susceptibility, can affect their proliferation. Malassezia species exhibit varied geographical distributions and host preferences; for instance, M. globosa, M. restricta, and M. sympodialis are predominant in humans, whereas M. pachydermatis is more common in dogs.
In dogs, colonization typically starts early in life, frequently in the peri-oral/lip region and interdigital skin, with population size and colonization frequency varying by site and breed. In cats, M. pachydermatis is prevalent, but other species are also found, particularly in the ear canal and claw fold. Next-generation sequencing has enhanced our understanding of these yeasts as part of the skin microbiota, revealing that while they're not the most abundant in dogs and cats, they are a significant component. Overall, M. pachydermatis is a standard inhabitant of the skin and mucosae in healthy dogs and cats, with the potential to proliferate and cause inflammation under certain conditions. The presence and population size of Malassezia yeasts on the skin are influenced by host species, breed, and environmental factors.
How do yeasts cause disease in a dog's or cat's skin?
The pathogenesis and immunological responses to Malassezia yeasts is focused on their transition from commensals to pathogens on host skin. Advances in genomic studies have led to a better understanding of the yeast's adaption to skin, revealing virulence attributes essential for colonization and infection. The yeasts, particularly M. globosa, M. sympodialis, M. restricta, and M. furfur, interact with the skin's immune system, potentially triggering inflammation.
These interactions include adherence of Malassezia cells to keratinocytes, which may stimulate or suppress immune responses. Changes in host immunity, skin microclimate, or concurrent diseases can predispose animals to clinical disease. Malassezia yeasts have evolved to rely on lipid sources due to an expansion of lipase and phospholipase genes and loss of carbohydrate metabolism genes. These enzymes may damage the epidermal barrier, contributing to skin lesions in diseases like dermatitis.
The yeasts' cell wall carbohydrates are recognized as allergens, triggering immune responses. In humans and dogs, Malassezia antigens can activate innate, antibody, and cell-mediated immune responses, often leading to hypersensitivity reactions. This interaction may result in either protective or harmful immune responses. Therefore, the pathogenesis of Malassezia infections involves a complex interplay between the yeast's metabolic activities, host immune responses, and interactions with other skin microbes. This balance determines whether the outcome will be inflammation or commensal carriage. These findings are crucial for developing new preventative and therapeutic strategies for skin diseases associated with Malassezia yeasts.
What are the predisposing factors for yeast infection?
Malassezia dermatitis, a condition arising from the overgrowth of commensal Malassezia yeasts, can be influenced by various predisposing factors affecting the skin's microclimate and leading to inflammatory skin disease.
1. Breed: Gender and age are not consistent predictors, but certain dog breeds, including West Highland White Terriers, English Setters, Shih Tzus, Basset Hounds, American Cocker Spaniels, Boxers, Dachshunds, Poodles, and Australian Silky Terriers, have shown a higher predisposition. Breeds with skin folds are also more prone to infections in intertriginous sites.
2. Cutaneous hypersensitivity disorders like atopic dermatitis can create conditions favorable for yeast overgrowth through skin barrier disruption and increased moisture or sebum production.
In cats, breeds like Devon Rex and Sphynx are more susceptible, often presenting with seborrhoeic skin conditions, especially in the claw folds.
2. Primary and secondary seborrhoeic conditions, as well as diseases causing aberrant cornification, can encourage Malassezia proliferation. The condition is also observed in conjunction with endocrinopathies like hypothyroidism and Cushing's disease/syndrome (hyperadrenocorticism). In cats, no direct correlation has been established between endocrinopathies and Malassezia overgrowth.
4. Environmental factors, such as climate, play a role in predisposing dogs to Malassezia overgrowth, with the condition being more common in tropical climates and warmer, humid months. However, the role of factors like immunosuppression and antibacterial therapy remains unclear, with anecdotal evidence suggesting both may influence yeast counts.
5. Idiopathic malassezia infections: Some cases of Malassezia dermatitis occur without identifiable concurrent diseases or predisposing factors, termed 'idiopathic'. This suggests a gap in understanding the complex immune interactions that determine skin colonization by these yeasts.
What are the clinical signs of Yeast Dermatitis?
Malassezia dermatitis in dogs can occur in any age, sex, or breed, but certain breeds have a higher predisposition. It's often first diagnosed in dogs aged one to three years, typically secondary to atopic dermatitis or due to genetic predispositions. The disease presents as pruritic dermatosis or otitis, with varying severity of pruritus. Seasonality is observed in some cases, coinciding with warmer, humid months.
The skin lesions can be localized or generalized, commonly occurring on the muzzle, lips, ventral neck, axillae, ventral abdomen, medial hindlimbs, interdigital skin, perineum, and external ear canal. Symptoms include diffuse erythema, kerato-sebaceous scale, greasiness, alopecia, and an offensive odor. Chronic cases might show hyperpigmentation and lichenification. Malassezia paronychia may also occur, characterized by reddish-brown staining of claws and inflammation of surrounding tissue.
Many dogs with Malassezia dermatitis have concurrent dermatoses like hypersensitivity disorders, bacterial pyoderma, endocrinopathies, or cornification defects. Diagnosis can be challenging due to overlapping clinical signs and the lack of direct correlation between yeast density and clinical manifestations. In some cases, especially in predisposed breeds, no underlying cause is identifiable, and the condition may respond completely to antifungal therapy.
In cats, Malassezia dermatitis varies depending on the underlying disease. It is associated with a greasy seborrhoeic dermatitis, often accompanied by paronychia. Predisposing factors in cats include genetic factors, atopic dermatitis, food reactions, flea bite hypersensitivity, and diabetes mellitus. Devon Rex and sphynx cats often show greasy seborrhoea with alopecia and hyperpigmentation. In allergic cats, the presentation can include pruritus, alopecia, erythema, and greasy exudate.
Cats may also present with idiopathic facial dermatitis, paraneoplastic alopecia, superficial necrolytic dermatitis, feline acne, and otitis externa associated with Malassezia. These conditions can vary in presentation, from erythema and scale to more severe symptoms like alopecia, pruritus, and secondary infections.
Malassezia dermatitis in dogs and cats, therefore, presents with a range of clinical signs, often associated with pruritus and kerato-sebaceous scale. The presence of concurrent diseases and breed predispositions can influence the presentation and severity of the disease.
How is Malassezia Yeast dermatitis diagnosed?
The assessment of Malassezia populations on canine and feline skin is crucial for understanding their cutaneous ecosystem in both health and disease. Traditional cytological and cultural methods have established Malassezia yeasts as normal inhabitants of healthy canine and feline skin and mucosae. Overgrowth of these yeasts is a feature of various clinical presentations in dogs and cats. Recent molecular techniques offer advantages in detecting minority populations or organisms unamenable to routine methods.
Quantitative methods for enumeration of yeasts in skin include impression cytology (using slides, tape, or culture) and dispersal methods (like cup-scrub or swab-wash). Tape-stripping has become popular in veterinary clinical practice for assessing cutaneous populations, particularly for rapid evaluation. Culture methods, such as contact plates and swab-wash techniques, vary in their efficiency, with some underestimating microbial populations.
Routine cytology using tape-strips or dry scrapes stained with a modified Wright Giemsa stain is recommended for veterinary clinics. Culture methods, while primarily providing qualitative data, can offer insights into the yeast population, especially when there's heavy growth. Detergent scrub sampling remains the 'gold standard' for quantitative culture but is more suited for research due to its practical limitations.
While various methods are available for sampling Malassezia populations in dogs and cats, their interpretation in a clinical context requires careful consideration of several factors, including anatomical site, breed, and immune status. Trial therapy is often needed to determine the clinical significance of observed yeast populations.
How is Malassezia Yeast Dermatitis treated?
Treatment of Malassezia dermatitis in dogs and cats generally involves the use of topical and/or systemic antifungal medications.
For topical treatment, shampoos containing antifungal agents like miconazole and chlorhexidine are effective.
The use of a 2% miconazole and 2% chlorhexidine shampoo, applied twice weekly, has strong evidence supporting its efficacy. A 3% chlorhexidine shampoo is also effective, with moderate evidence.
In terms of systemic treatments for dogs, there is moderate evidence supporting the use of ketoconazole at a dosage of 5–10 mg/kg orally once or twice daily, and itraconazole at 5 mg/kg orally once daily or on two consecutive days per week.
Fluconazole, at 5–10 mg/kg orally once daily in conjunction with cefalexin, has limited evidence and requires further evaluation. Terbinafine shows some beneficial effects, but further studies are needed for a stronger recommendation. It is important to avoid compounded formulations of azole medications due to unreliable bioavailability.
For cats, there is weak evidence supporting the use of itraconazole at 5–10 mg/kg orally once daily or on a seven days on/off protocol. Topical treatments with chlorhexidine and azole products, although not extensively evaluated, are considered sensible for adjunctive or sole treatments in localized infections.
In both dogs and cats, it is crucial to diagnose and treat any underlying causes contributing to the proliferation of Malassezia yeasts. The choice of treatment may depend on factors like regional availability, regulatory status, cost, and the ability of the owner to effectively apply topical products.
How is Malassezia Yeast Infection Prevented?
The prevention of Malassezia-associated skin diseases in dogs and cats mainly involves managing underlying diseases and regular topical or pulsed oral antifungal therapy, particularly when predisposing factors can't be identified or controlled.
For topical therapy, regular use of antifungal treatments like 2% chlorhexidine/2% miconazole or 3% chlorhexidine shampoo is recommended. These shampoos have been effective in treating Malassezia dermatitis and may help prevent relapses when used twice weekly. Hydrocortisone aceponate, applied twice weekly, also shows potential in preventing Malassezia otitis externa associated with allergic skin diseases. However, the evidence supporting weekly antifungal shampoo bathing as a preventive strategy is more anecdotal than evidence-based.
Pulsed oral antifungal therapy is another strategy for preventing recurrent Malassezia dermatitis and otitis. Itraconazole, dosed at 5 mg/kg orally once daily for two consecutive days per week, has been effective in treatment and might also work as a preventative measure. However, there is a potential risk for developing antifungal drug resistance with pulsed dosing. Ketoconazole, at 5–10 mg/kg orally once daily for two consecutive days per week, is also suggested based on anecdotal reports, although itraconazole is generally considered safer.
The use of Malassezia allergen-specific immunotherapy has been proposed and shown some positive outcomes in studies, but the evidence remains low, and further research is required to assess its benefits as a preventative approach.
Overall, when predisposing factors for Malassezia overgrowth can't be controlled, regular treatment is often necessary to minimize relapses, with a preference for topical treatments due to lower toxicity risks. Pulsed oral antifungal therapy could also be an option, but the potential for resistance development should be considered.
Any chances of zoonosis between pets and humans?
Malassezia yeasts, including M. pachydermatis, are common on the skin of both animals and humans. While their presence alone doesn't prove zoonotic transmission, it suggests potential cross-species interactions. M. pachydermatis is typically found on healthy human skin, particularly on the face and hands. This species has been implicated in various human skin diseases like seborrhoeic dermatitis, though its pathogenic role in humans is generally attributed to contact with pets.
Genotyping studies of M. pachydermatis have shown different haplotypes specific to certain animal species, with some also found in humans. This yeast predominates on many human body sites and is present from birth, increasing in the first weeks of life. It has been isolated from human clinical specimens, including skin, body fluids, and blood.
The most well-documented zoonotic aspect of M. pachydermatis is its role in fungaemia in pre-term neonates receiving lipid-rich nutritional infusions via catheters. Outbreaks in neonatal intensive care units (NICUs) have been linked to a single strain of M. pachydermatis, transmitted from health care workers’ hands and pet dogs. In adults, M. pachydermatis has been associated with systemic infections in immunocompromised patients.
A study showed that dog owners, especially those with atopic dogs affected by Malassezia, are more likely to have M. pachydermatis on their hands. Good hand hygiene is crucial to prevent transmission, particularly in healthcare settings. The overall risk of M. pachydermatis as a zoonotic agent is low, especially among individuals who are not severely immunocompromised. However, the importance of hand hygiene for individuals in contact with pets is emphasized.
1. Nakabayashi A, Sei Y, Guillot J. Identification of Malassezia species isolated from patients with seborrhoeic dermatitis, atopic dermatitis, pityriasis versicolor, and normal subjects. Med Mycol 2000; 38: 337–341.
2. Chang HJ, Miller HL, Watkins N, et al. An epidemic of Malassezia pachydermatis in an intensive care nursery associated with colonization of health care workers’ pet dogs. N Engl J Med 1998; 338: 706–711.
3. Morris DO. Malassezia pachydermatis carriage in dog owners. Emerg Infect Dis 2005; 11: 83–88.
4. Guillot J, Bond R. Malassezia pachydermatis: a review. Med Mycol 1999; 37: 295–306.
5. Bensignor E, Hahn H, Guillot J. Topical vs. systemic treatment of Malassezia dermatitis in dogs: a comparative, blinded, randomised trial. Vet Dermatol 2012; 23: 84 (abstract).
6. Bensignor E. Oral itraconazole as a pulse therapy for the treatment of canine Malassezia dermatitis: a randomized, blinded, comparative trial. Pratique Médicale et Chirurgicale de l’Animal de Compagnie 2006; 41: 69–72.
7. Pinchbeck LR, Hillier A, Kowalski JJ, et al. Comparison of pulse administration versus once daily administration of itraconazole for the treatment of Malassezia pachydermatis dermatitis and otitis in dogs. J Am Vet Med Assoc 2002; 220: 1807–1812.
8. Cafarchia C, Figueredo LA, Otranto D. Antifungal susceptibility of Malassezia pachydermatis biofilm. Med Mycol 2013; 51: 863–867.
9. Prohic A, Jovovic Sadikovic T, Krupalija-Fazlic M, et al. Malassezia species in healthy skin and in dermatological conditions. Int J Dermatol 2016; 55: 494–504.
10. Chen TA, Hill PB. The biology of Malassezia organisms and their ability to induce immune responses and skin disease. Vet Dermatol 2005; 16: 4–26.
I as zoonotic agents17.1 BackgroundCharacterizing the zoonotic potential of pathogenicagents is always