A superficial skin disease usually lasting no more than 6 months.

AETIOLOGY

Usually Trichophyton verrucosum or Microsporum canis.

PREVALENCE

TRANSMISSION

Direct or indirect contact. Infected premises. Buying in calves. Rarely from man to cattle.

CLINICAL SIGNS

Lesions are most common around the eyes and at the base of the ears. Neck, back and perineum are often affected but lesions are uncommon on the lower limbs.

The first sign of cattle ringworm is a palpable thickening of the affected skin. Next, the overlying hair pattern is disturbed. As infection progresses and inflammation develops the bases of hairs become matted with a light coloured exudate and eventually asbestos-like crusts, grey or fawn in colour, develop. The lesions may be present singly or coalesced into groups. They are usually rounded and discrete, less often diffuse and confluent. They are somewhat itchy. Hairs generally break off at the surface of the lesion. Mechanical removal of the crust of an active lesion reveals moist red skin and the crust later reforms.

The fungus invades the keratin of the hair follicle and the hair shaft just above the bulb. Secondary bacterial infection may follow. The immunity produced is not solid.

EPIDEMIOLOGY

While other species (including man) can be infected, cattle are important as the reservoir for T. verrucosum. The fungus can survive for years off the animal.

DIAGNOSIS

The classical mature lesion of cattle ringworm is clinically diagnostic. Rarely, however, atypical lesions occur, e.g. scaliness and hair loss only.

Certain stains can be diagnosed by there ability to fluoresce under an ultraviolet light. Microscopical examination or fungal culture can confirm the diagnosis.

TREATMENT AND CONTROL

Griseofulvin is no longer available in a form for farm use as a feed additive. The license has been withdrawn. The small dosage and short course recommended by the manufacturer were not very effective in severe cases. More effective was 20mg active principle per kg body weight daily for 14 days. Although this involves using griseofulvin outwith the data-sheet recommendations and appropriate withdrawal periods would be required.

Topical antifungal applications include natamycin and eniconazole. These preparations may be more useful for individuals or small groups of animals due to time taken to apply fluids topically but the nil milk (and meat) withdrawal periods may be advantageous.

Evaluation of any treatment in clinical trials is made very difficult by the spontaneous regression of the lesions which occurs without treatment, especially alter animals are turned out to grass in the spring. A vaccine against ringworm caused by T.verrucosum has been marketed. The attenuated vaccine is given from 2 weeks of age and is repeated 10-14 days later, alter which no subsequent booster doses are required.

Sterilisation of premises is near impossible.