ANIMAL PARASITES IN NOSE AND SINUSES OF HEAD 25 



It is usually better to slaughter the affected animals and 

 thoroughly disinfect the pens. As the disease is spread by 

 the infected nasal discharge, a separation of the healthy 

 from the sick is indicated. 



ANIMAL PARASITES IN THE NOSE AND SINUSES 

 OF THE HEAD. 



Grub in the Head of Sheep. OEstrus Ovis. 



Definition. — A catarrh of the nasal chambers and sinuses 

 of the head due to the larvse of the bot fly, CEstrus ovis. 



Occurrence. — ^Found in all countries where the sheep bot 

 exists. Australia is said to be exempt. Few American 

 sheep are free from grub. 



Etiology. — ^The sheep are usually attacked by the parent 

 bot fly during the hot season. It is said that the fly may 

 even be active in winter in warm, simny sheepfolds. 



Life History. — The larvae are deposited by the swift-flying 

 female bot on the margin of the sheep's nostrils, from whence 

 they crawl up into the nasal chambers, cavities of the turbi- 

 nal bones, ethmoid cells and even horn cores. It is possible 

 that the brain is invaded in some cases. They attach them- 

 selves to the mucous membrane to feed and develop. They 

 usually remain in the sheep about ten months, or until the 

 following spring when they leave via nasal passages and 

 reach the ground. In the soil in one or two days they pass 

 into the chrysalis form out of which emerges in six to eight 

 weeks the mature bot fly. The impregnated female bot 

 seeks sheep herds. She usually hides in cracks and crevices 

 in the sheep barn or on shrulabery or underbrush near the 

 sheep pasture. Sheep try to avoid the attacks of the fly 

 by running away, from it with their noses held close to the 

 ground or by grouping themselves in a great mass, their 

 heads toward the center. If the fly touches the nostril, the 

 sheep will snort, stamp its feet and rub its nose on the fore- 

 legs or ground. They often seek dusty places in the pasture 

 to avoid the fly. Once the larvse have gotten into the head. 



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