Bovis ISSN 2398-2993

Ringworm

Synonym(s): dermatophytosis

Contributor(s): Catherine Fraser , Peter Down

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Introduction

  • Cause: fungal infection of hair shafts and stratum corneum, usually by Trichophyton verrucosum occasionally by T mentagrophytes and Microsporum canis.
  • Signs: annular alopecia, broken hairs, variable scaling and crusting mainly on head and neck and periocular in youngstock.
  • Diagnosis: clinical signs often diagnostic, also skin scapes, hair plucks and fungal isolation.
  • Treatment: spontaneous recovery in 1-4 months is usual, vaccination is available (Bovilis® Ringvac. MSD Animal Health).
  • Prognosis: good.
Print off the farmer factsheet on Ringworm to give to your clients.

Pathogenesis

Etiology

  • Trichophyton verrucosum  Trichophyton spp zoophilic, by far the most common isolate from cases of dermatophytosis in cattle, fomites are important in transmission
  • Trichophyton mentagrophytes found in soil though nor geophilic, wild animal reservoir in foxes and rodents
  • Microsporum canis zoophilic uncommon.
  • Trichophyton equinum zoophilic uncommon.
  • Microsporum nanum geophilic.
  • Microsporum gypseum geophilic.

Predisposing factors

General

  • Particularly calves under 1 year of age.
  • Housed animals most at risk with darkness, and moisture both predisposing factors.
  • Groups of calves loose-housed in covered yards characteristically affected.
  • Long-lived nature of dermatophyte spores leads to infection of susceptible stock year on year.

Pathophysiology

  • Spores are picked up from other infected cattle by direct contact or by contact with fomites.
  • Spores may be present in soil or via wild rodents and other animal species eg T. mentagrophytes.
  • Having been acquired, fungi penetrate to the hair follicles and the stratum corneum.
  • Infection is restricted to keratin-bearing tissues.
  • Fungi multiply rapidly leading to congestion of the skin by perivascular accumulation of monocytes.
  • Skin becomes inflamed and swollen and hair stands up on end.
  • Arthrospores are formed along the hair shaft (ectothrix) and also inside the hair shaft (endothrix).
  • Hairs break off and small circular alopecic patches appear.
  • Alopecic patches become red and inflamed as inflammation progresses, skin becomes moist and scales and crusts appear, composed of epithelial cells, serum exudate and fungal hyphae.
  • Crusts eventually fall off and as the infection never reaches the mitotic region of the hair follicle once the old dead hair is shed, hair follicles produce new hairs.

Timecourse

  • Initial incubation period is 7-14 days.
  • Clinical signs start at days 14-28.
  • Crust formation days 28-45.
  • Regression days 45-60.

Epidemiology

  • Youngstock are most susceptible not as a result of age per se but due to a lack of immunity. Hence older stock may show signs of disease if they are naive to infection.
  • Sale yards, introduction of new unquarantined stock may both predispose.
  • Winter group housing of youngstock in overcrowded, humid, dark conditions predisposes to infection.
  • Poor hygiene between successive groups allows infection to persist from year to year.
  • Spores may be viable within the environment for up to 5 months and may remain viable in skin scale for up to 4 years.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed Papers

  • Recent references from PubMed and VetMedResource.
  • Gooding R & Lund A (1995) Immunoprophylaxis of Bovine Dermatophytosis. Can Vet J 36 (5), 302-306 PubMed.

Other sources of information

  • Andrews A H (1997) Skin Diseases of Farm Animals. Royal Veterinary College Modular Course Notes.
  • Van Cutsem J & Rochette F (1991) Mycoses in Domestic Animal. Janssen Research Foundation.
  • Scott D W (1988) Large Animal Dermatology. W B Saunders.


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