impaginato piccolo - Società Italiana di Parassitologia (SoIPa)

Parassitologia 50: 81-83, 2008
Diagnostic and clinical features of animal malasseziosis
S. Nardoni 1, M. Corazza 2, F. Mancianti 1
1 Dipartimento di Patologia Animale, Profilassi ed Igiene degli Alimenti, Università di Pisa. Viale delle Piagge, 2 56124 Pisa;
2 Dipartimento di Clinica Veterinaria, Università di Pisa. Via Livornese lato monte, San Piero a Grado Pisa.
Abstract. Malassezia yeasts infection represents a common clinical concern with a special regard to canine
dermatology. The Authors review the main clinical features of malasseziosis in canine and feline medicine,
summarizing predisposing factors and aetiopathogenesis of the yeasts’ infection. A special reference was
given to clinical and microscopical diagnosis.
Key words: Malassezia, diagnosis, otitis, dermatitis, dog.
The genus Malassezia includes 13 species of lipophilic,
nonmycelial, unipolar budding yeasts characterized by
a thick cell wall. Malassezia spp. are component of the
cutaneous mycoflora of many warm-blooded animals
included man. Malassezia pachydermatis, which is the
sole not lipidodependent species, in dogs is considered
as a commensal yeast and probably adheres to the skin
corneocytes by tripsin-sensitive protein adhesion molecules.
It is frequently isolated from the external ear
canal, from the skin, particularly the anal area which
could be a carriage zone, oral mucosa, vagina and eye
of healthy dogs (Chen T and Hill PB, 2005; Prado MR
et al., 2008; Scott DW et al., 2004). M. pachydermatis
is also recovered from the distal hair in healthy dogs,
but hair follicle carriage is infrequent and at that site
yeast burden is low. In healthy dogs, Malassezia yeasts
were most frequently isolated in the perianal and perioral
areas, and in a study it has been established that
Malassezia spp. are present in 15.7% of dogs in anal
sac content, with no difference between healthy dogs
and dogs with Malassezia dermatitis associated with
atopic dermatitis.
Despite Malassezia spp. are part of normal skin
mycoflora, the yeast may become pathogen in certain
circumstances. In dogs with atopic dermatitis there is
indirect evidence of transepidermal penetration of antigens
and subsequent phagocytosis by Langherans cell
that present antigen to T-cells initiating the cascade of
immunologic responses. This leads to the destruction
of the yeasts or to their mechanical removal via scaling.
The pathogenic role of Malassezia spp. yeasts is
unknown and it seems to be mainly related to a disturbance
of the normal physical, chemical or immunological
mechanisms that allow Malassezia pachydermatis
to multiply and to become pathogenic. Variation of
antigenic expression in different growth phases of M.
pachydermatis could explain discrepancies among
studies about immune response to the yeasts.
Correspondence: Simona Nardoni
Dip Patologia Animale, Profilassi ed Igiene degli Alimenti,
Università di Pisa, Viale delle Piagge, 2 56124 Pisa (Italy)
Tel + 39 050 2216952; fax + 39 050 2216941
e-mail: snardoni@vet.unipi.it
Skin abnormalities enhancing Malassezia overgrowth
are: excessive moisture and amount of sebum or cerumen,
disruption of the epidermal barrier and intertrigo.
The most common diseases acting as underlying causes
of Malassezia dermatitis are allergies, pyoderma,
demodicosis, keratinization disorders and endocrine
disturbancies. Otitis are commonly complicated by
yeasts overgrowth. Malassezia spp. were isolated from
41.2%-72.9% of cats and from 57.3%-62.2%of dogs
with otitis externa. M. pachydermatis, either as a pure
culture or in association with lipid-dependent species,
was identified in most of all specimens (97%).
(Nardoni S et al., 2004; Cafarchia C et al., 2005;
Nardoni S et al., 2007)
Immunological dysfunction could also promote growth
of the Malassezia population on the skin. For instance,
epidermal dysplasia of the West Highland White Terrier
could be associated with a genetic predisposition to a
poor response of T-cells towards the yeast, despite the
inability of yeast to stimulate keratinopoiesis.
Malassezia spp. produce enzymes, such as phospholipases,
that alter the cutaneous lipidic film, pH and proteases
that induce inflammation and pruritus through
proteolysis and complement activation. In facts, the
frequency of isolation and population size of
Malassezia species were higher in dogs with localized
dermatitis, especially in affected areas, indicating a role
of Malassezia in the occurrence of skin lesions.
Dogs with Malassezia dermatitis have greater concentration
of specific IgG than normal subjects, whereas
atopic dogs, with or without concurrent Malassezia
dermatitis, have higher levels of specific IgG and IgE
than non-atopic dogs with Malassezia dermatitis or
normal dogs. Skin testing with a Malassezia extract
shows immediate hypersensitivity reactions and atopic
dogs with cytologic evidence of Malassezia dermatitis
had an increased lymphocyte blastogenic response to
crude M. pachydermatis extracts, compared with clinically
normal dogs and dogs with Malassezia otitis. In a
study on atopic dogs, no statistical correlation between
the presence of cutaneous alterations and Malassezia
isolation was detected. Highest scores were not exclusively
found on affected areas, but also on lesion-free
sites, demonstrating that atopic animals can be heavily
colonized also in apparently healthy areas.