Can Dogs and Cats Get Yeast Infections? Understanding the Causes and Symptoms

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?

Skin anatomy

Skin anatomy

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 mechanism of an allergic reaction

The mechanism of an allergic reaction

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.

Skin dermatitis on a dog

Skin dermatitis on a dog

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.

Atopic dermatitis in dog, Cocker spaniel breed

Atopic dermatitis in dog, Cocker spaniel breed

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.

Closeup dog ear problem,show the secondary skin infections in dogs with Atopic Dermatitis

Closeup dog ear problem,show the secondary skin infections in dogs with Atopic Dermatitis

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.

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