Experimental bovine Trichophyton verrucosum infection. Preliminary clinical, immunological and histological observations in primarily infected and reinoculated cattle.

Summary The cutaneous application of different doses of viable Trichophyton verrueosum to the unabraded skin of cattle of various ages resulted in clinically recognizable ringworm infection of varying extent and duration. Confluent lesions covering the whole inoculated area were produced by 10 7 viable units of the fungus, whereas the minimal infective dose of 10 3 viable units produced limited areas of infection only. The level of nutrition within the limits imposed had no effect on the extent or severity of lesions. The fungus was found to invade the keratinized portions of skin and hair of cattle of all ages at the same rate. However, both the cutaneous inflammatory response and the resolution of lesions were most rapid in older animals. The ability to eliminate infection more rapidly was associated with a marked delayed hypersensitivity response commencing 14 days after infection. Such hypersensitivity was not detectable by this means after the resolution of lesions. T. verrueosum could not be isolated in culture from skin lesions until 21 days after inoculation and could only be isolated for half the period that lesions were present. Cattle were resistant to cutaneous reinfection with viable T. verrueosum on previously infected or fresh skin sites at 2 months and at more than one year after the resolution of primary lesions. A mild delayed hypersensitivity response developed in every site within 48 hr. of reinoculation. The intravenous inoculation of previously-infected cattle with 10 4 viable units of T. verrueosum resulted in an immediate-type cutaneous reaction at the original site of infection.