Page 217 - WSAVA2018
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M. Burrows1
1Murdoch University Division of Veterinary and Biomedical ScienceMurdoch, Western Australia
Malassezia pachydermatis is a non-mycelial yeast. It is approximately 2 x 4 micrometers in size, has an oval shape with a thick wall and reproduces by unipolar budding. This gives the organism its characteristic
shape. There are at least 13 species of lipid dependent yeast including M. sympodialis, M equine, M. caprae, M. cuniculi (colonising animals skin) and the rest: M. furfur, M. globosa, M. obtusa, M. restricta, M slooffiae, M dermatis, M. japonica and M. yamatoensis colonising human skin. M. pachydermatis is present as a commensal of the skin and mucosae of most dogs. In clinically normal dogs,
the sites most frequently colonised by M. pachydermatis are the ear canals, anus, lips, chin, interdigital skin, rectum and vagina. It is uncommon on the axilla, groin or dorsum. The anus seems to be the most frequently colonised mucosal site.
It is now clear that under certain circumstances, Malassezia can change from being a commensal organism to a significant pathogen. For this to occur, there has to be alteration in the skin microclimate that allow the organism to proliferate to excessive levels. These changes may involve increased temperature and humidity, changes in skin lipids, alteration in epidermal barrier function and the presence of concurrent bacterial infection. Since S. pseudintermedius and M. pachydermatis are inhabitants of the mucosae, including the oral cavity, they will continually be transferred to
the skin, particularly in areas which require cleaning or grooming, and which are pruritic. Thus there is potential for the establishment of microbial overgrowth whenever the skin is damaged or there is underlying disease impairing cutaneous function. These abnormalities may occur in association with:
• Allergic skin diseases
• Epidermal abnormalities (hepatocutaneous syndrome,
zinc-responsive dermatoses)
• Endocrine diseases (Hyperadrenocorticoidism, Hypothyroidism)
• Breed associated susceptibility (Basset Hound, Dachshund, Cocker Spaniel, West Highland White Terriers, Miniature poodles, German shepherds, Cavalier King Charles Spaniel are at higher risk)
• Prior treatment with antibiotics: suggested but not corroborated. Unlike Candida spp, Malassezia is not inhibited by bacteria but is enhanced by the increased growth of S. pseudintermedius.
Malassezia pachydermatis most commonly causes
as pruritic dermatitis that can affect the lips, muzzle, periocular region, ventral neck, axillae, interdigital areas, body folds, medial thighs and perineum. In the ear canals, Malassezia causes an erythematous, ceruminous otitis. Depending on the sites affected, Malassezia dermatitis may present as foot chewing, frantic face rubbing, ear scratching, perianal licking or scooting or more generalised pruritus.
Commonly affected areas
It is important to note that all these sites may not be affected in an individual dog. Also in severely affected dogs, the lesions can become more generalised.
The lesions seen in these areas consist of erythema, often covered by a yellow or slate-grey waxy scale. The skin may feel greasy to touch and there may be
an offensive, rancid odour. With time, the lesions may become hyperpigmented or develop into erythematous plaques. Chronic lesions are often lichenified. Pruritus may be quite marked. Malassezia overgrowth can
also be detected in the claws of some dogs resulting in a reddish-brown staining of the proximal claw or a waxy exudate in the claw fold, with inflammation of the surrounding soft tissue. In dogs, Malassezia paronychia is commonly associated with atopic dermatitis and paw licking.
There is good evidence to support the role of M.pachydermatis as an allergen in canine atopic dermatitis. This situation, known as Malassezia hypersensitivity, can occur alongside reactivity to
other allergens or it can occur in isolation. Clinically, Malassezia hypersensitivity in dogs manifests as a
highly inflammatory and pruritic response mounted to relatively low numbers of yeast organisms, though some dogs may also have overt infection with cytologically evident overgrowth. Clinical diagnosis of Malassezia hypersensitivity in the dog relies upon intradermal allergy testing, or by measuring serum allergen specific IgE. Recent studies have demonstrated good correlation between IDAT reactivity and allergen specific IgE in atopic dogs. In humans, the clinical implications of a
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