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Avian Influenza
A study of the H5N1 virus

--general info and chapters
--introduction
--full document (pdf)

Superficial Dermatitis
Ringworm
Dermatophytosis

--general info
--research
--treatment
--references

Malassezia
Malassezia pachydermatis
--general info
--research
--treatment
--references

Mud Fever
D. congolensis

--general info
--barrier-cream
--research
--references
--treatment

MRSA in Pets
Methicillin Resistant
Staphylococcus aureus

--MRSA Research
--Pet-bedding
--Barrier-cream
--Newspaper clip

--Press Release
--Treatment
--Link
--Pricelist


Anti-microbial research applications
--gallery
--health benefits
--background info
--Press Release
--research
--link

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Equine cutaneous microflora
Normal resident bacteria
--general info
--research
--references

Equine gut microflora
probiotics
--general info
--research
--references

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Veterinary Microbiology

Malassezia dermatitis (Malasseziasis)
- a research extract
-

Malassezia pachydermatis (previously known as Pityrosporum canis) is a commensal lipophilic yeast (Guillot & Bond, 1999) found on the majority of external ear canals on the canine species (Mason et al, 1996). M. pachydermatis has been found on the human scalp, without clinical signs of infection (Harding et al, 2002); it has also been isolated from equine skin, in the groin region, although its clinical significance is currently unknown (Nell et al, 2002).
Pathogenic invasion may occur in the superficial epidermal layers if changes in the microclimate arise, this may be caused by increased sebum production, moist maceration of the skin, trauma, allergies or bacterial infection (Patterson, 1998). The invasion of
M. pachydermatis can lead to secondary ear and skin infections (Mason et al, 1996) such as otitis externa and seborrheic dermatitis (Lloyd, 1993).
As found in human dandruff sufferers, cutaneous sensitivity was increased. This may be due to an impaired barrier function in the scalp caused by a combination of reduced free fatty acids, cholesterol and ceramides, which form a critical part of the epidermal water barrier. This weakened barrier allowed the invasion of
M. pachydermatis (Harding et al, 2002).
Resistance to fungal infections can be natural or acquired. Natural resistance mechanisms such as phagocytic cells can engulf fungi, particularly where they invade around the hair follicle and the secretion of sebum containing fatty acids has an inhibitory effect on fungi proliferation (Hay, 1993). However the fatty acid residues that inhibit dermatophytes often support the growth of Malassezia yeast (Hay, 1993).
With acquired resistance to superficial mycoses, elevated levels of immunoglobulin E (IgE) have been associated with chronic infections as they can trigger a rapid release of histamine (Tizard, 2000). Patients with seborrheic dermatitis were found to have higher titres of IgG and IgM against antigens of
M. pachydermatis isolates. However, no correlation has been found between the development of an antibody response and the recovery of dermatophytosis (Hay, 1993).
M. pachydermatis can cause a type I atopic hypersensitivity reaction in those sensitive to its presence. Kroger et al (1996) and Chen et al (2002) suggested that an IgE mediated immune response might be clinically important in the pathogenesis of disease, as animals suffering with a M. pachydermatis infection showed a greater IgE response than non infected animals.
Bond et al (1998) demonstrated that high densities of
M. pachydermatis were not associated with serum IgA deficiency. However, dogs with M. pachydermatis associated skin disorders frequently developed high serum titres of M. pachydermatis -specific IgG and modest increases of IgA in comparison to healthy dogs. Although, high serum IgG and IgA do not prevent M. pachydermatis-related skin disease as chronic disease development can still occur in the presence of these titres.
Certain healthy and also affected individuals can develop cell-mediated immune responses to the antigens associated with this commensal yeast. Lower stimulation indices in affected Basset Hounds indicate that their lymphocytes were less responsive to this antigen, a difference that may be of significance in the development of disease. However, it was not clear whether the lower stimulation indices were a cause or an effect of the microbial skin infection (Bond et al, 1998).
Breed predisposition to
M. pachydermatis is thought to be due to the presence of skin folds (Guaguere & Prelaud, 1996), with susceptible breeds including West Highland White Terriers, Basset Hounds and Cocker Spaniels (Patterson, 1998; Bond et al, 1998).
As the predisposing factors are general problems,
M. pachydermatis may appear as a secondary disease, which could make diagnosis difficult.