Canis ISSN: 2398-2942

Trichophyton spp

Contributor(s): Richard Walker

Introduction

Classification

Taxonomy

  • Phylum: Ascomycota.
  • Family: Gymnoascaceae.
  • Genus: Trichophyton.
  • Some consider both Microsporum and Trichophyton to be members of the genus Arthroderma.

Etymology

  • Greek:trikho- hair /phyton- plant.

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Clinical Effects

Epidemiology

Habitat

  • Main reservoir hosts of Trichophyton species include dogs, horses, cattle, cats, pigs, monkeys and poultry.
    Can transfer to in-contact humans.

Lifecycle

  • Reproduces both sexually (via ascospores, found only in the non-parasitic phase), and asexually.
  • Asexual reproduction occurs in the non-parasitic phase via microconidia and occasionally macroconidia.
  • Asexual reproduction occurs during the parasitic phase via arthroconidia.

Transmission

  • Most commonly occurs through direct contact but also fomites.
  • Source of canine infection is most commonly an infected cat.

Pathological effects

  • Dermatophytes are able to hydrolyze keratin and cause some damage to the epidermis and hair follicle.
  • A hypersensitivity reaction is then mounted and the fungus moves away from the site of inflammation to normal skin.
  • This causes the classic circular ringworm lesion with healing at the center and inflammation at the edge.
  • Antibody-mediated and cell-mediated hypersensitivities involved in pathogenesis.
  • Antibodies not imported in resistance.
  • Recovered animals are resistant to re-infection, but may show severe local reactions on exposure.
  • Proteolytic enzymes → virulence.
  • Infectious conidium enters through skin defect → germination → mycelium develops in cornified epithelium → hair invasion → ectothrix arthroconidial accumulation.
  • Site of lesion depends on reservoir and transmission, eg T. erinacei (the reservoir host being the hedgehog) occurs on muzzle, face, front paws and legs of dogs which worry hedgehogs .T. eqinum survives in fomites (such as tack and grooming equipment), and so occurs in horses in those areas which come into contact.

Other Host Effects

  • Some species have become adapted for survival in the skin of specific host species, ie they are zoophilic, eg T. erinacei (European hedgehogs), T. mentagrophytes (rodents), T. verrucosum (cattle).

Control

Control via chemotherapies

  • Spontaneous regression without treatment is common.
  • Topical: clotrimazole Clotrimazole , and tolnaftate.
  • Clipping around affected areas and topical treatment with povidone-iodone Povidone-iodine , or chlorhexidine Chlorhexidine.
  • Ketoconazole may not be as effective.
  • Oral: griseofulvin Griseofulvin.
  • Topical treatment may decrease spread.

Control via environment

  • In infected cat colonies. In-contact animals should also be treated.

Vaccination

  • In cattle. Has been attempted experimentally in horses.

Other countermeasures

  • Clip hair from affected site.

Diagnosis

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Further Reading

Publications

Refereed papers

  • Recent references from VetMed Resource and PubMed.
  • Parker W M & Yager J A (1997) Trichophyton dermatophytosis - a disease easily confused with pemphigis erythematosus. Can Vet J 38(8), 502-5.
  • White-Weithers N & Medleau L (1995) Evaluation of topical therapies for the treatment of dermatophyte-infected hairs from dogs and cats. JAAHA 31(3), 250-3.
  • Sparkes A H, Gruffydd-Jones T J, Shaw S E et al (1993) Epidemiological and diagnostic features of canine and feline dermatophytosis in the United Kingdom from 1956 to 1991. Vet Rec 133(3), 57-61.

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