Common equine parasite wrongly identified in textbooks – study

A stained chromosome pair inside an egg of Parascaris univalens.
A stained chromosome pair inside an egg of Parascaris univalens.

A recent study has 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. univalensis is the main roundworm species now observed in equines.

The broader designation Parascaris spp. should be used instead, unless cytological characterization – a technique for characterizing chromosomes – has confirmed the species.

“Parascaris univalens is really the forgotten parasite,” said lead researcher Martin Nielsen, an assistant professor with the University of Kentucky Gluck Equine Research Center

“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 possesses one germ line chromosome pair as opposed to two for P. equorum, but the two species are otherwise considered structurally identical. The germ line refers to fertilized egg cells harvested before their first cell division.

“We really wanted to find specimens of both species to study and find differences in their DNA,” Nielsen explained.

“The only way to tell them apart is to look at their chromosomes, so we invited a leading expert, Dr Clara Goday, to the Gluck Equine Research Center to teach us the delicate technique of parasite karyotyping.”

Karyotyping is a technique to study and characterize chromosomes in a sample of cells.

For the study, 30 live worms were obtained and dissected. All of the samples were identified as P. univalens. Then, the karyotyping technique was performed on ascarid eggs from foal fecal samples. P. equorum was not identified among these, whereas P. univalens was found in 17 samples, with the remaining eight being inconclusive.

“We were part of another study analyzing numerous Parascaris specimens from several different continents, and the conclusion there was that only one species was found,” Nielsen said.

“We compared genetic information obtained for P. univalens in our study with gene codes already published as P. equorum and found that they were probably mislabeled.”

Other researchers from UK Gluck Center involved in the study were Jennifer Bellaw, a doctoral student in veterinary science; Professor Eugene Lyons; and Association Professor Teri Lear. The Gluck group collaborated with Assistant Professor Jianbin Wang and Professor Richard Davis, from the University of Colorado School of Medicine; and Clara Goday at Centro de Investigaciones Biologicas in Spain.

Their findings were published in the December issue of Parasitology Research.

Reporting: Jenny Evans

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