Fungal
Dermatitis or Superficial Mycosis
Esther van Praag, Ph.D.
Warning: this file contains
pictures that may be distressing for people.
Mycosis is not common in either wild or house rabbits and is rarely
encountered as epizootic. Rather, it generally occurs as a sporadic infection
in one individual rabbit, in young rabbits, or in sick debilitated rabbits.
It is believed that immunosuppressed rabbits are more susceptible to the
disease.
The causing agents are two pathogenic fungi:
- Trichophyton
mentagrophytes = ringworm
May be carried asymptomatically in the coat of the rabbit.
- Microsporum
canis
Occasionally rabbits are infected through contact with cats or dogs;
this fungus can carry one or more zoonotic diseases (diseases that can be
transmitted from animal to human).
Ringworm is the main cause of mycosis. It will infect not only the epidermis, but
also the annex structures such as hair follicles and hair shafts. In some
cases, cultures of infected tissue have revealed the presence of Microsporum
sp.
Clinical signs
Typically, lesions
start around the head and spread to the legs and feet, more specifically to
the toenail beds. The wound is raised, circumscribed and erythematous. It
shows dry crusts with little or no pruritus and patchy alopecia. The tissue
under the crusts usually shows inflammation and the hair follicles show
abscessation, as the secondary result of a bacterial invasion.
Histological sections show hyperkeratosis, folliculitis, acanthosis
and the diffuse infiltration of leukocytes into the dermis layer.
Diagnosis
1. Cultures on a fungal or
dermatophyte media. It must, however, be kept in mind that the results
obtained may not be reliable and must be completed with histological studies.
2. Identification of skin
scrapings mounted in 10% KOH. This enables to identify the different
arthrospores
3. Fluorescence
(UV light) is of little help. One fungus (Trichophyton
mentagrophytes) does not fluorescence; the other fungus (Microsporum
canis) is strain dependent: some show fluorescence,
others do not.
4. Gomori
methenamine silver stain, Gridley fungus stain and periodic acid-Schiff (PAS)
reaction staining are all methods that help demonstrate the presence of
arthrospores and to identify them.
The diagnosis must differentiate from other causes
of crusty alopecia commonly found on the head and ears (genetic hairlessness,
trauma, depilatory hair loss, fur pulling).
Treatment
The hair around
the lesion should be clipped, and disposed off safely.
The best treatment for fungal dermatitis is oral administration of
griseofulvin (25-50 mg/kg PO q24h or divided q12h). (Wear gloves while
administering this drug). The treatment should continue two weeks after the
disappearance of the clinical signs.
Topical or
systemic treatments are also possible:
• Clotrimazole cream or lotion;
• Enilconazole spray;
• Itraconazole (5-10 mg/PO, q 24 h);
• Terbinafine (8-20 mg/kg PO, q24h);
• Ketoconazole (10-15 mg/kg PO q 24h) (not to
be used in breeding animals);
• Miconazole cream.
Most of the available products are unlicensed for use in rabbits;
literature references, however, assert those drugs are the treatments of
choice for fungal dermatitis in rabbits.
The environment of the rabbit should be cleaned
carefully: vacuum cleaning, boiling of towels and cleaning of surfaces with
1:10 bleach water.
Acknowledgement
Thanks are due to Lynne Huntley (USA)
and to Kathleen Hermans, D.V.M. (Kliniek voor Pluimvee en Bijzondere Dieren, Universiteit Gent, Belgium) and
to Prof. Richard Hoop (Institut für Veterinärbakteriologie, University of
Zurich, Suisse) for their pictures.
Further
information
K. L. Banks, T. B. Clarckson (1967) Naturally occurring dermatomycosis in the rabbit. J. Am.
Med. Assoc. 151: 926-29.
K. W. Hagen (1969) Ringworm in domestic rabbits:
Oral treatment with griseofulvin. Lab Anim. Care 19: 635-638.
E. V. Hillyer, K. Quesenberry, S. Valkoff (1997)
Ferrets, Rabbits and Rodents: Clinical Medicine and Surgery, (Editor)
Saunders W B Co, p. 215.
L. M. Vogstberger et
al. (1986) Spontaneous dermatomycosis due to Microsporum canis in
rabbits. Lab. Anim. Sci. 36: 294-97.
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