HERPES— RINGWORM 289 



less troublesome it is a benign disease. Horses are also 

 affected with it, as are sheep and pigs. 



Etiology. — ^Ringworm is caused by the fungus Trichophyton 

 tonsurans. This fungus is made up of threads (hyphee) 

 which are interwoven to form mycelia and large, round, light- 

 refracting spores which predominate. The fungus lives in 

 the hair sac, where it produces an inflammation of the hair 

 follicle, causing the hair to fall out, and also within the hair 

 shaft, which it makes brittle, causing it to break off. Infec- 

 tion is spread by direct contact or through intermediary 

 agents, such as posts, stall partitions, etc., against which 

 affected animals have rubbed themselves. Harness, saddles, 

 and grooming utensils are also carriers. 



Forms. — ^Four forms of herpes tonsurans are distinguished 

 clinically, depending upon the species of animals attacked and 

 the location and age of the lesion: (a) Herpes tonsurans 

 which is characterized by round, bald spots without inflam- 

 mation of the skin. (6) Herpes circinatus the center healing 

 but the periphery remaining diseased thus forming a hoop- 

 shaped, circular lesion — hence the name "ringworm." (c) 

 Herpes maculosis occurring on the skin of old animals and 

 leading to alopecia and a superficial chronic dermatitis with 

 desquamation of the epidermis which forms slate-gray colored, 

 asbestos-like scales, (d) Herpes vesiculosus which attacks 

 the thin skin of young animals (calves, lambs). This is a 

 dermatitis with vesicle formation. The vesicles soon rupture 

 forming thick, yellow, scaly scabs or crusts in the neighbor- 

 hood of the mouth, face and eyes. 



Cattle. — ^In adult cattle herpes usually attacks first the 

 head and neck, where it forms small, well-defined, round, bald 

 spots which by confluence may reach the size of an open 

 hand. These areas are covered with grayish-white, asbestos- 

 like crusts. On black skin the crusts are thicker than on 

 white. The skin is sometimes thickened and creviced. 

 Healing usually takes place under the crusts in two or three 

 months. When there is much pruritus, causing rubbing and 

 scratching, secondary lesions form, prolonging the course of 

 the disease several months. 



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