Parascaris univalens–a victim of large-scale misidentification?

The research paper investigates the horse ascarid parasite known as Parascaris univalens, which has been largely ignored despite its potential implications for anthelmintic resistance and clinical disease. The study finds evidence to suggest that P. univalens may be the main species currently infecting horses, questioning the typical identification of these parasites as Parascaris equorum.

Objective and Methodology

• The purpose of this study was to examine Parascaris univalens, a parasite species previously not given much attention, but which could potentially have significant implications for both health care and pest control in the equine world.
• To carry out the investigation, the research team took live worm samples from the University of Kentucky’s parasitology horse herd. They dissected and identified these samples using karyotyping techniques, which look at the genetic make-up of cells.
• The researchers adapted these techniques to analyze ascarid eggs from fecal samples taken from 25 Thoroughbred foals at three farms in Central Kentucky, further extending their study population.

Main Findings

• All worm specimens from the University of Kentucky (30 in total) were identified as Parascaris univalens, not the commonly assumed Parascaris equorum.
• Of the 25 fecal samples analyzed, none identified the presence of P. equorum. Instead, P. univalens was found in 17 samples, with the rest being inconclusive.
• A male worm identified as P. univalens was subjected to mitochondrial genome sequencing. The resulting assembly and annotation were compared with sequence reads labeled as P. equorum. The results showed only 0.16% nucleotide differences, casting doubt on the accuracy of existing genetic information labeled as P. equorum in public databases.

Significance and Implications

• The findings suggest that P. univalens may be the main species now observed in equines, rather than the usually assumed P. equorum. This raises important implications for the naming and identification of such parasites.
• The research team suggest that unless cytological characterization has confirmed the species, the designation Parascaris spp. (indicating an unspecified species within the Parascaris genus) should be used.
• The study highlights the potential for large-scale misidentification of P. univalens as P. equorum, showing the importance of proper species identification in parasitic control and health care in equine populations.