DNA testing for dangerous horse parasite has potential to become routine, scientists suggest

Adult Strongylus vulgaris, or bloodworms.
Adult Strongylus vulgaris, or bloodworms. © Martin Krarup Nielsen

DNA-based testing has proven its worth in detecting the presence of one of the most dangerous horse parasites and should now be considered a routine diagnostic method, according to scientists.

Strongylus vulgaris is the most pathogenic of the large strongyles, or large redworms.

Its larvae migrate in the arteries that supply the large intestines. The larvae cause endarteritis and thrombosis and may result in blockages of the arteries and intestinal infarctions.

Often, by the time its eggs are detected in horse faeces, the damage has already been done.

It can take the larvae six months or more to mature into egg-producing adults. During this time the migrating larvae are virtually undetectable with traditional tests.

Now, in research based at Germany’s Ludwig-Maximilians-University, scientists have compared two detection techniques – one old and one new.

The traditional method was larval cultures while the more modern method is known as real-time polymerase chain reaction (PCR) testing. It is a laboratory technique used in molecular biology that targets DNA for identification.

Alexandra Kaspar and her colleagues, writing in the journal BMC Veterinary Research, said reliable detection of S. vulgaris was essential, given its pathogenic nature.

In their study, faecal samples from 501 German horses were screened for S. vulgaris using real-time PCR, with an additional larval culture performed on the samples of 278 horses.

A subset of 26 horses underwent multiple follow-up examinations with both methods to evaluate both the persistence of S. vulgaris infections and the reproducibility of each diagnostic method.

Real-time PCR testing revealed S. vulgaris DNA in 10 of the 501 investigated equine samples (1.9%).

The larval culture revealed larvae of S. vulgaris in three of the 278 samples (1.1%).

A direct comparison of the two methods was possible in 321 samples, including 43 follow-up examinations. There were 11 S. vulgaris-positive samples by real-time PCR and 4 S. vulgaris-positive samples by larval culture.

“The real-time PCR detected a significantly higher proportion of positives of S. vulgaris compared to larval culture and should thus be considered as a routine diagnostic method for the detection of S. vulgaris in equine samples,” the researches concluded.

The authors noted that larval cultures for the detection of S. Vulgaris, while cost-effective, were time-consuming, given the development period of up to 14 days for strongyle larvae.

They said the use of real-time PCR for the detection of S. vulgaris as a routine method was possible in any laboratory with appropriate equipment for the real-time PCR-procedure.

Detection of Strongylus vulgaris in equine faecal samples by real-time PCR and larval culture – method comparison and occurrence assessment
A. Kaspar, K. Pfister, M. K. Nielsen, C. Silaghi, H. Fink and M. C. Scheuerle
BMC Veterinary Research 2017 13:19 DOI: 10.1186/s12917-016-0918-y

The study, published under a Creative Commons License, can be read here

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