HYPODERMA LINEATUM— WARBLE FLIES 291 



Etiology. — ^The disease is not very common, but occurs 

 occasionally enzootically. The pustules are caused by the 

 acne bacillus. Infection takes place usually through inter- 

 mediary agents, such as harness and saddles. 



Symptoms. — ^In the regions noted round or oval swellings 

 the size of a 25-cent piece appear, which in a day or so 

 become covered with small, hempseed-sized vesicles, which 

 rapidly form pustules. The pustules usually break in twenty- 

 four to thirty-six hours, forming thick, yellow, sticky crusts 

 which heal in about two weeks. There is usually little or no 

 pruritus. In severe cases boils or even abscesses may form 

 as in simple acne. The abscesses may rupture, forming 

 ulcers which heal under the scab. In rare instances an 

 inflammation of the lymph vessels and glands complicate the 

 case. Healing in these cases requires one to two months. 

 This form of contagious pustulous dermatitis may resemble 

 skin glanders. However, even in the most severe cases there 

 are no general symptoms. 



Diagnosis. — ^The location, absence of itching and contagious 

 character differentiate contagious pustulous dermatitis from 

 acne or other suppurative conditions of the skin due to 

 traumatism. 



Treatment. — ^The patient should not be worked, the sick 

 isolated from the healthy, and the pustules opened and 

 treated with antiseptics. The harness, saddle, and stable 

 should be disinfected. 



HYPODERMA LINEATUM. WARBLE FLIES. 



The cattle bot, or warble ily, one variety of which appears 

 in the United States, produces serious discomfort to cattle 

 and damage to hides, due to the perforations which they 

 cause in the skin of the shoulder, back, and breast. 



Life History. — The female gadfly deposits her eggs in 

 summer, while the cattle are on pasture, in the region of the 

 heel where they are licked off by the animal reaching the 

 mouth and throat where they hatch. The larvae perforate 

 the gullet and, following the course of the bloodvessels in 

 the mediastinal tissue, reach the vertebral foramina, through 



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