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DNA helps in detection of deadly bloodworm in horses

Bloodworm larvae (arrows) in the cranial mesenteric artery of the horse. Inflammation of the vessel wall and thrombus formation is pronounced.
© Dr. Ray M. Kaplan, University of Georgia

August 29, 2007

A Danish Ph.D. student from the University of Copenhagen has developed a novel diagnostic method for detection the horse bloodworm, Strongylus vulgaris.

The bloodworm has its name because of extensive migrations in the blood vessels of the horse. After ingestion on pasture, larvae dwell in the blood stream for about four months and cause severe reactions, leading to "thrombo-embolic colic", a disease syndrome characterized by severe manifestations of pain.

The condition has a poor prognosis, and often death is the outcome.

Bloodworm eggs are not morphologically different from the majority of parasite eggs in equine faeces, and a conclusive diagnosis of bloodworm infection can only be reached after two weeks of coproculture and subsequent microscopic identification of hatched larvae. This is clearly time-consuming and requires considerable technical skills from the microscopist identifying the bloodworm larvae.

"Nowadays, we recommend minimal deworming to prevent further development of anthelmintic resistance as much as possible. At many horse establishments in Denmark, people deworm twice yearly or less, and the choice of treatment is based on faecal examination", explains Dr Martin Krarup Nielsen, DVM from University of Copenhagen.

"The coproculture method is labour-intensive and not fully reliable, and as a consequence, some horses are being under-treated, while others are over-treated".

Dr Nielsen spent part of his study time at University of Georgia, USA and used the real-time polymerase chain reaction (PCR) technique to develop his assay designed for detecting bloodworm DNA in faecal samples. The assay can detect down to a single bloodworm egg among a thousand parasite eggs in a sample, and it can quantify the number of bloodworm eggs. The instrumentation can analyse 96 samples at the time, and the whole procedure can be completed within a working day.

"We now have a powerful and reliable diagnostic tool for monitoring the bloodworm of horses, which will be of benefit for horses world-wide", says Dr Nielsen. He will be presenting his work at international conferences in Washington DC, USA and Ghent, Belgium later this year.



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