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Parascaris equorum
''Parascaris equorum'' is a species of ascarid that is the equine roundworm. Amongst horse owners, the parasites are colloquially called "Ascarids." This is a host-specific helminth intestinal parasite that can infect horses, donkeys, and zebras. It cannot infect humans or other animals. It is yellow-white in color, and females can become as large as in length.〔 Found worldwide, ''P. equorum'' is one of the most difficult equine parasites to kill, requiring larger doses of more powerful anthelmintic medications than are needed for other equine parasites.〔
==Life cycle ==
''P. equorum'' is sexually dimorphic, the females are significantly larger than males. Mating occurs in the small intestine of the equid. The female is able to lay over 170,000 eggs in a day, and 60,000,000 eggs in a year. Eggs have a thick, multilayered shell for protection and the ability to adhere to any surface they touch once expelled.〔 Eggs are expelled in feces, which are then consumed by a horse while eating contaminated grass or drinking contaminated water. In a three-month life cycle, the swallowed eggs become larva and migrate from the small intestines into blood vessels and from there travel to the liver, where they molt into another larval stage. From there, they migrate to the lungs, where they emerge from blood vessels into the alveoli.〔 They spend between 14 to 17 days migrating through the liver and lungs.〔 At this point, they are coughed up and re-swallowed, where the larvae mature into adult roundworms that produce eggs.〔 The worms take from 79 to 110 days to reach adulthood. ''P. equorum'' lives by sucking up the liquid contents of the intestine and may occasionally also suck blood from the intestinal wall.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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