The yeasts of the genus Malassezia have been of recognised clinical importance since the 1990s. Malassezia are lipophilic yeasts (increased growth in the presence of lipids) but not lipo-dependent (they can grow without lipids) like other yeast species. They appear as small spherical or ovoid microscopic elements. They reproduce by budding, creating a scar-like swelling on the mother cell. This bulge gives the yeast a peanut, keel or "Russian doll" appearance.
They are part of the normal skin and ear flora of healthy dogs. They are found preferentially on the lips, interdigital spaces, limbs, thorax, abdomen, vaginal and anal areas.
Malassezia in cats is not a classic finding. Serious internal disease should be sought.
Basset Hounds, Shih Tzu, Beagles show a racial predisposition to the onset of malassezia-related dermatitis (skin inflammation). Allergic dermatitis such as canine atopic dermatitis, endocrinopathies (hypothyroidism...) and many other dermatoses are risk factors. However, the breeds that are prone vary from country to country! Excessive humidity, hypersecretion of earwax or sebum and the presence of skin folds favour the appearance of Malassezia dermatitis.
Malassezia dermatitis is characterised by pruritus (biting, licking, scratching), erythema (redness), sometimes alopecia (hair loss) and an oily, scaly condition of the skin (dandruff). A rancid smell is common. The anterior neck, head, interdigital spaces, ars and groins are the most commonly affected body areas.
Malassezia otitis is very common. It is characterised by tickling of the ears, erythema (redness) and soft to dry brown earwax.
Diagnosis is based on the clinical appearance of the lesions and evidence of yeast by cytological examination (surface swab or earwax swab for microscopic examination). Fungal cultures are rarely performed as cytology is usually sufficient to confirm clinical suspicion.
For Malassezia dermatitis, an underlying or associated dermatosis should always be sought. The treatments used for mycoses are recommended in topical (external) or systemic (oral) form.
For Malassezia otitis, various ear drops or ointments containing antifungals are recommended.
PS: Chronic ear infections with black, rancid-smelling earwax are much more often related to the presence of Malassezia than to the persistence of an ear parasite. Recurrent ear infections are very rare. Ask your vet to confirm the diagnosis by cytological examination!