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.