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) 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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