Dermatophytosis in Cattle
Trichophyton verrucosum is the usual cause of ringworm in cattle, but T mentagrophytes, T equinum, Microsporum gypseum, M nanum, M canis, and others have been isolated. Dermatophytosis is most commonly recognized in calves, in which nonpruritic periocular lesions are most characteristic, although generalized skin disease may develop. Cows and heifers are reported to develop lesions on the chest and limbs most often, and bulls in the dewlap and intermaxillary skin. Lesions are characteristically discrete, scaling patches of hair loss with gray-white crust formation, but some become thickly crusted with suppuration. Ringworm as a herd health problem is more common in the winter and is more commonly recognized in temperate climates and in English rather than Zebu breeds of cattle.
Many topical treatments have been reported to be successful in cattle, but because spontaneous recovery is common, claims of efficacy are difficult to substantiate. Valuable individual animals should still be treated, because this may well limit both progression of existing lesions and spread to others in the herd. Thick crusts should be removed gently with a brush, and the material burned or disinfected with hypochlorite solution. Treatment options depend on allowed usage of some agents in animals destined for slaughter. Agents reported to be of use include washes or sprays of 4% lime sulfur, 0.5% sodium hypochlorite (1:10 household bleach), 0.5% chlorhexidine, 1% povidone-iodine, natamycin, and enilconazole. Individual lesions can be treated with miconazole or clotrimazole lotions.
A live attenuated fungal vaccine is in use in some countries other than the USA. The vaccine has been used in control and eradication programs to successfully decrease the number of new infected herds. The duration of immunity is long lasting. The vaccine prevents development of clinical lesions, transmission to other animals, and contamination of the environment. A vaccination program combined with a cleaning and disinfection protocol can help eliminate signs of ringworm and eradicate it from the herd. Vaccination has greatly reduced the incidence of zoonotic disease in farmers, their households, veterinarians, and people working in abattoirs and tanneries. No live attenuated vaccine is available in North America.