A recent study led by Martin Nielsen, DVM, PhD, Dipl. EVPC, ACVM, assistant professor at the University of Kentucky (UK) Gluck Equine Research Center, found that all veterinary medicine textbooks have misidentified a common equine parasite.

The large equine roundworm Parascaris equorum, commonly referred to as the ascarid, which is known for infecting foals, is actually a different species—Parascaris univalens. The research suggests P. univalens is the main species now observed in equines. The broader designation Parascaris spp. should be primarily used unless cytological characterization (a technique for characterizing chromosomes) has confirmed the species.

“Parascaris univalens is really the forgotten parasite,” Nielsen said. “It is almost never mentioned in the textbooks, and most people have only heard about one roundworm species infecting equids.”

P. univalens was discovered more than 130 years ago. The species only possesses one germ line chromosome pair as opposed to two for P. equorum, but the two species are otherwise considered structurally identical