Ringworm is common in animals of the bovine species, but very rare in other domesticated animals, except, perhaps, the horse. It is caused by the growth of a parasite, Trichophyton mentagrophytes (Robin), of the genus Trichophyton, family Gymnoascea, order Ascomycetes.
The ascosporaceous form of reproduction is still unknown, but the mode of reproduction by conidia is characteristic. In cultures the mycelium is represented by growing filaments branching off at right angles, and by separate superficial aerial reproductive filaments of the conidian form. There is some reason for believing that these fungi may lead a saprophytic as well as a parasitic existence, i.e., that they can exist and multiply apart from the animal body.
Their vitality is marked. Various experimenters have transmitted the disease with crusts kept for eighteen months. Thin declares that in two and a half years the spores had lost all power of germination. They resisted immersion in water for two days, but were dead after eight days. Soft soap and 1 per cent. acetic acid kill them in an hour.
Symptoms. The disease most frequently attacks young animals and milch cows—very rarely adults or old animals. This peculiarity is very difficult to explain.
In calves, ringworm seems specially to attack the head, the neighbourhood of the lips, the nostrils and submaxillary region, as well as the throat and neck. It assumes the form of circular patches, over which the hair stands erect.
Gruby in 1842 discovered the parasite of tinea tonsurans, or herpes, and thus proved that the cutaneous lesions were not due to any constitutional condition, as was long thought, although dirt, bad hygienic conditions, and crowded stables favoured the spread of ringworm.
Fig. 266.—Calf suffering from ringworm.
Direct contact between healthy and diseased animals and the transport of spores, by combs, brushes, etc., favour contagion. The disease may not only be conveyed from one animal to another of the same species, but from the ox to man, and, with somewhat greater difficulty, from the ox to the horse. Cases of transmission from the ox to the sheep, pig, and dog have also been recorded.
Mégnin in 1890 attempted to prove that all the trichophytons producing ringworm in animals do not belong to the same species, and gave the name of Trichophyton epilans to that usually found in the ox, because it causes absolute loss of the hair by growing in the follicle, whilst he named the parasite found in the horse Trichophyton tonsurans, because it only grows on the surface of the skin and in the thickness of the hair, without causing inflammation of the hair follicle and without invading it.