New Method for Detecting Bloodworms

Strongylus vulgaris (the bloodworm) is the most pathogenic parasite infecting horses worldwide.

Photo: Martin Krarup Nielsen, DVM, PhD, Dipl. EVPC

Strongylus vulgaris, commonly known as the bloodworm, is considered the most pathogenic parasite infecting horses worldwide. But scientists have until now not been able to develop a reliable diagnostic method for detecting migrating larvae of S. vulgaris.

A group of scientists from the University of Kentucky Gluck Equine Research Center and the Department of Large Animal Sciences at the University of Copenhagen in Denmark have developed a novel, reliable assay for detection of S. vulgaris in the bloodstream.

Martin Nielsen, DVM, PhD, Dipl. EVPC, assistant professor at the Gluck Equine Research Center, described S. vulgaris as the most dangerous of all equine parasites, largely due to its extensive larval migrations in the horse's arterial system. The larvae make their way to the horse's bloodstream and spend about four months there before returning to the intestine. During their migration the larvae cause a pronounced inflammation in the arterial wall and cause large blood clots to form. Smaller clots can detach and travel down larger blood vessels until they block smaller vessels. This can deprive parts of the intestinal tract from oxygen and nutrients and cause life-threatening colic.

Currently, detection of S. vulgaris infection is based on a time-consuming larval culture with subsequent microscopic examination or a recently developed PCR detecting DNA extracted from parasite eggs. No diagnostic method has been proven useful for detecting migrating larvae of S. vulgaris while still in the blood, Nielsen said. The larval culture and PCR assay both detect the adult worms present in the intestine. Adult worms are not believed to cause disease, and when they are detected in a horse, serious damage in the blood vessels might have occurred months earlier.

These issues highlighted a need for reliable and improved diagnostic tools to diagnose S. vulgaris while still in the blood, Nielsen said.

“We used gene technology to identify potential diagnostic molecules and found one interesting antigen, which we named rSvSXP after characterizing and expressing it as a recombinant protein,” he said.

The scientists extracted RNA from S. vulgaris worms and larvae and used this to construct an S. vulgaris genetic library consisting of about five million expressed genes. They identified one of these gene products to have diagnostic potential. The protein was then fully sequenced, expressed recombinantly, and validated with serum samples from 102 horses with known infection status. Additionally, they constructed an ELISA assay with sensitivity and specificity of 73.3% and 81%, respectively.

The ELISA assay has been proven capable of diagnosing the larvae while migrating in the blood vessels, so the horse can be diagnosed and treated right away before further damage occurs. Overall, Nielsen said, this is a major advancement over currently available diagnostic methods.

“Our first results are very promising, and we are hoping we can further develop diagnostic assays using this protein,” Nielsen said.

He said a patent has been filed and the researchers are currently seeking financial partners in an attempt to make a test commercially available. They have gained interest from potential partners, but a diagnostic product likely will not be launched for several more years.

Shaila Sigsgaard is an editorial assistant for the Bluegrass Equine Digest.

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