Onychomycosis Caused by Malassezia pachydermatis in a Dog

Abstract

Background: Malassezia species are commensal skin organisms of warm-blooded vertebrates that can act as opportunistic pathogens. Malassezia pachydermatis is of importance in both veterinary and human medicine. Recognised initially as causes of infection of the skin, they are now known to be superficial commensals as well as potential causes of infections in domestic animals and more serious human conditions such as fungemia. They have also been implicated in the pathogenesis of allergic and other inflammatory diseases. Onychomycosis is defined as fungal infection of the claw (nail disease) caused by dermatophytes (Microsporum and Trichophyton genus), non-dermatophyte molds (hyaline and dematiaceous) and/or yeasts. The objective of this work was to report a case of canine onychomycosis by Malassezia pachydermatis based on reference standard diagnostics of this pathology.Case: A 9-year-old male West Highland White Terrier presented history of claw abnormality: brown staining and partly brittle. The dog has no apparent history of trauma on the affected claw and no skin disease was reported. Direct examination of claw was performed using the tape strip technique revealed Malassezia organisms. Nail fragments were cultured onto Sabouraud Dextrose Agar with Chloramphenicol and Cycloheximide. After 10 days of incubation (32ºC) nail fragments allowed the isolation of pure colonies of Malassezia pachydermatis. The histopathological evaluation was performed by Sector of Veterinary Clinical Pathology, Faculdade de Veterinária (FAVET/UFRGS) and fungal infection due to Malassezia pachydermatis was confirmed by histopathologic examination (Hematoxylin and eosin and Grocott’s methenamine silver stain) of the nail, that revealed abundant yeasts (blastoconidia).Discussion: Fungal infection of the skin, hair and nails are common and are primary caused by the dermatophyte molds. Non-dermatophyte molds isolated from nails constitute a long list, but only a few species cause onychomycoses. These include Scopulariopsis brevicaulis, Fusarium sp., Acremonium spp., Aspergillus spp., Penicillium spp. Yeasts like Malassezia and Candida spp. are saprophytes and usually represent incidental contaminants associated with a non-sterile specimen at mycological culture, however in some cases they may parasite the nails and become an etiological agent of the disease. M. pachydermatis, normally present on the skin and in the ear canal of dogs and cats, can act as opportunistic pathogenic microbe and frequently causes dermatitis and otitis in mammals. In the case of onychomycosis, there is little evidence that Malassezia yeasts are implicated in nail plate invasion, although this may be a rare occurrence. All species of the genus are obligatory lipid-dependent forms, with the exception of M. pachydermatis, as well as absence of keratinolytic ability. Malassezia organisms were commonly retrieved from the subungual claw fold region of normal healthy dogs (should be considered resident microflora of the normal canine claw fold). Some authors suggests that high numbers of yeast can be detected on cytological evaluation of the skin surface of the canine claw fold from allergic dogs in both the absence and presence of concurrent signs of pruritus and paronychia.

Full text

ISSN 1679-9216
1
CASE REPORT
Pub. 412
Acta Scientiae Veterinariae, 2019. 47(Suppl 1): 412.
DOI: 10.22456/1679-9216.94817
Received: 4 April 2019 Accepted: 17 July 2019 Published: 16 August 2019
1Setor de Micologia & 2Setor de Patologia Veterinária (SPV), Departamento de Patologia Clínica Veterinária (DPCV), Faculdade de Veterinária (FaVet),
Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, RS, Brazil. CORRESPONDENCE: A. Spanamberg [spanamberg.ad@gmail.com]
& L. Ferreiro [laerte.ferreiro@ufrgs.br]. Av. Bento Gonçalves n. 9090. Bairro Agronomia. CEP 91540-000 Porto Alegre, RS, Brazil.
Onychomycosis Caused by Malassezia pachydermatis in a Dog
Andréia Spanamberg1, David Driemeier2, Luciana Sonne2 & Laerte Ferreiro1
ABSTRACT
Background: Malassezia species are commensal skin organisms of warm-blooded vertebrates that can act as opportunistic
pathogens. Malassezia pachydermatis is of importance in both veterinary and human medicine. Recognised initially as
causes of infection of the skin, they are now known to be superficial commensals as well as potential causes of infections in
domestic animals and more serious human conditions such as fungemia. They have also been implicated in the pathogenesis
of allergic and other inflammatory diseases. Onychomycosis is defined as fungal infection of the claw (nail disease) caused
by dermatophytes (Microsporum and Trichophyton genus), non-dermatophyte molds (hyaline and dematiaceous) and/or
yeasts. The objective of this work was to report a case of canine onychomycosis by Malassezia pachydermatis based on
reference standard diagnostics of this pathology.
Case: A 9-year-old male West Highland White Terrier presented history of claw abnormality: brown staining and partly
brittle. The dog has no apparent history of trauma on the affected claw and no skin disease was reported. Direct examination
of claw was performed using the tape strip technique revealed Malassezia organisms. Nail fragments were cultured onto
Sabouraud Dextrose Agar with Chloramphenicol and Cycloheximide. After 10 days of incubation (32ºC) nail fragments
allowed the isolation of pure colonies of Malassezia pachydermatis. The histopathological evaluation was performed by
Sector of Veterinary Clinical Pathology, Faculdade de Veterinária (FAVET/UFRGS) and fungal infection due to Malassezia
pachydermatis was confirmed by histopathologic examination (Hematoxylin and eosin and Grocott’s methenamine silver
stain) of the nail, that revealed abundant yeasts (blastoconidia).
Discussion: Fungal infection of the skin, hair and nails are common and are primary caused by the dermatophyte molds.
Non-dermatophyte molds isolated from nails constitute a long list, but only a few species cause onychomycoses. These
include Scopulariopsis brevicaulis, Fusarium sp., Acremonium spp., Aspergillus spp., Penicillium spp. Yeasts like Malas-
sezia and Candida spp. usually are saprobics and usually represent incidental contaminants associated with a non-sterile
specimen at mycological culture, however in some cases they may parasite the nails and become an etiological agent of
the disease. M. pachydermatis, normally present on the skin and in the ear canal of dogs and cats, can act as opportunistic
pathogenic microbe and frequently causes dermatitis and otitis in mammals. In the case of onychomycosis, there is little
evidence that Malassezia yeasts are implicated in nail plate invasion, although this may be a rare occurrence. All species
of the genus are obligatory lipid-dependent forms, with the exception of M. pachydermatis, as well as absence of kerati-
nolytic ability. Malassezia organisms were commonly retrieved from the subungual claw fold region of normal healthy
dogs (should be considered resident microflora of the normal canine claw fold). Some authors suggests that high numbers
of yeast can be detected on cytological evaluation of the skin surface of the canine claw fold from allergic dogs in both
the absence and presence of concurrent signs of pruritus and paronychia.
Keywords: dog, nail, Malassezia pachydermatis, onychomycosis.

2
A. Spanamberg, D. Driemeier, L. Sonne & L. Ferreiro. 2019. Onychomycosis Caused by Malassezia pachydermatis in
a Dog. Acta Scientiae Veterinariae. 47(Suppl 1): 412.
INTRODUCTION
Diseased claws will predispose to trauma,
abnormal locomotion, pain, lameness, and pododer-
matitis. Various medical terms are used to describe
the claw lesion, being onychomycosis the term used
when a fungal infection occurs. Dogs with Malassezia
infections show brown-red discoloration of the claw
with brown-colored waxy exudate on the proximal
aspects of the claws [1,3].
Several species are currently recognized in the
genus Malassezia, most of which are lipid-dependent
(M. furfur, M. globosa, M. obtusa, M. restricta, M.
sloofiae, M. sympodialis, M. dermatis, M. nana, M.
japonica, M. yamatoensis, M. equina, M. caprae, M.
cunniculi) and only one non lipid-dependent (M. pa-
chydermatis). Genomic analysis has allowed a more
reliable classification of the yeasts that constitute the
genus Malassezia [2,7].
This yeast has been isolated from most domes-
tic animals, wild animals and free living in various
regions of the world. The finding of an apparent spe-
cificity by some hosts suggests a possible increase in
the discovery of new species of Malassezia in other
animal species [1,7].
Cytology, culture and histopathology have
already been used for the quantitative and qualitative
research of M. pachydermatis obtained from various re-
gions of the body, both healthy animals and those with
dermatopathies, but it was not possible to standardize
or determine the most effective. Mycological culture
continues to be the reference standard for evaluating
and comparing results, especially regarding the sen-
sitivity and specificity of alternative techniques [7].
The aim of this study was to report a case of canine
onychomycosis by Malassezia pachydermatis based
on the standard reference diagnosis.
CASE
A 9-year-old male West Highland White Ter-
rier, was referred to a private veterinary clinic, with a
history of claw abnormality: brown staining and partly
brittle. The dog has no apparent history of trauma on
the affected claw and no skin disease was reported.
Direct examination of claw was performed using the
tape strip technique revealed Malassezia organisms.
Nail fragments were cultured onto Sabouraud Dextro-
se Agar with Chloramphenicol and Cycloheximide1.
After 10 days of incubation (32ºC) the mycological
culture of nail fragments allowed the isolation of pure
colonies of Malassezia pachydermatis (Figure 1).
The histopathological evaluation was performed by
Sector of Veterinary Clinical Pathology, Faculdade
de Veterinária (FAVET/UFRGS) and fungal infection
due to Malassezia pachydermatis was confirmed by
histopathologic examination (Hematoxylin and eosin
and Grocott’s methenamine silver stain) of the nail (Fi-
gure 2), that revealed abundant yeasts (blastoconidia).
DISCUSSION
Yeasts of the genus Malassezia are commensal
skin organisms and can act as opportunistic pathogenic
microbe on human and mammalian skin [1], being fre-
quently reported in the Brazilian veterinary literature
[9]. Many factors may be associated with the prolifera-
tion of Malassezia yeasts in animals, including breed,
gender, and age. Nett et al. [11] reported that basset
hounds, cocker spaniels, and West Highland white
terriers are breeds predisposed to develop Malassezia
dermatitis. Alteration of microenvironmental skin
conditions connected to a chemical mechanism (pH
modifications), long-term treatments (antibiotics and
glucocorticoids), or presence of other bacteria or fungi
and coexisting diseases may contribute to Malassezia
proliferation [3,14].
Fungal infection of the skin, hair and nails are
common and are primary caused by the dermatophyte
molds. Non-dermatophyte molds isolated from nails
constitute a long list, but only a few species cause
onychomycoses. These include Scopulariopsis brevi-
caulis, Fusarium sp., Acremonium spp., Aspergillus
Figure 1. Pure colonies of Malassezia pachydermatis isolated on BD Sa-
bouraud Agar with Chloramphenicol and Cycloheximide. Nail fragments
were obtained from a case of onychomycosis in a dog.

3
A. Spanamberg, D. Driemeier, L. Sonne & L. Ferreiro. 2019. Onychomycosis Caused by Malassezia pachydermatis in
a Dog. Acta Scientiae Veterinariae. 47(Suppl 1): 412.
spp., Penicillium spp. Yeasts like Malassezia and
Candida spp. are saprophytes and usually represent
incidental contaminants associated with a non-sterile
specimen at mycological culture, however in some
cases they may parasite the nails and become an etio-
logical agent of the disease [4,7,10].
M. pachydermatis, normally present on the
skin and in the ear canal of dogs and cats, can act as
opportunistic pathogenic microbe and frequently cau-
ses dermatitis and otitis in mammals. Physical and che-
mical factors that enable the attachment of Malassezia
and the consequent infection, other conditions that may
contribute to Malassezia overgrowth are: hormonal im-
balance, keratinization defects (idiopathic seborrhea),
excessive production of sebum, bacterial infections,
and hypersensitivity processes [1,8,9]. In the case of
onychomycosis, there is little evidence that Malassezia
yeasts are implicated in nail plate invasion, although
this may be a rare occurrence [5,6]. All species of the
genus are obligatory lipid-dependent forms, with the
exception of M. pachydermatis, and lack enzymes for
keratolytic activity. Malassezia is lipophilic and since
nails are not good sources of lipid and since there are
no lipids under the nail plate, they do not colonize
nails. It is not clear whether Malassezia is a pathogenic
agent but therapeutic success has been achieved with
antifungals and hence it is not considered as primary
pathogen in onychomycosis [1,12,13].
Malassezia organisms were commonly retrie-
ved from the subungual claw fold region of normal
healthy dogs (should be considered resident microflora
of the normal canine claw fold). Some authors suggests
that high numbers of yeast can be detected on cytologi-
cal evaluation of the skin surface of the canine claw fold
from allergic dogs in both the absence and presence of
concurrent signs of pruritus and paronychia [1,8,11].
In the case reported here, onychomycosis due
Malassezia pachydermatis in a dog was confirmed
based mycological and histopathological findings.
MANUFACTURER
1BD - Becton Dickinson. São Paulo, SP, Brazil.
Declaration of interest. The authors report no conflicts of
interest. The authors alone are responsible for the content and
writing of the paper.
Figure 2. Histopathology of dog’s nails with onychomycosis. A- Nail with numerous typical micromorphologic structures (blastoconidia) of Malassezia
pachydermatis (Hematoxylin and Eosin, obj.40x). B- Numerous stained blastoconodia (Grocott’s methenamine silver stain, obj.40x).
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A. Spanamberg, D. Driemeier, L. Sonne & L. Ferreiro. 2019. Onychomycosis Caused by Malassezia pachydermatis in
a Dog. Acta Scientiae Veterinariae. 47(Suppl 1): 412.
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