Thursday, February 13, 2014

Detecting larval Strongylus vulgaris infections

 Collaboration between scientists in Denmark and the United States has led to the development of a diagnostic test that promises to help identify horses infected with the larval stages of the large strongyle Strongylus vulgaris. The larvae  migrate in the arteries that supply the large intestines and may cause blockage of the arteries and intestinal infarctions.

The result of the research is a serum enzyme-linked immunosorbent assay (ELISA) which has been validated for detecting migrating larvae in the bloodstream of horses. The test detects antibodies against a polypeptide in the excretory/secretory fraction of the migrating larvae, named SvSXP.

Further work using the test showed that foals receive colostral antibodies from the mare which may persist for up to 13 weeks of age. Foals start being able to mount their own immune response to the parasites from about three months of age, depending on the grazing conditions and the stage at which they were exposed to the parasites.

In younger foals, the serum ELISA does not give reliable diagnostic information despite heavy infections. The researchers found that young foals can be heavily infected without showing positive ELISA test results.

They also found that higher infection levels tend to be associated with higher ELISA levels.

Once they had started producing antibodies, foals continued to maintain high ELISA levels throughout the study. There was a tendency for the ELISA levels to decline gradually as the numbers of migrating larvae declined and adult intestinal worm burdens increased.

The scientists suggest that further research into the time taken for antibody levels to decline after effective anthelmintic treatment would be very useful.

If the test becomes commercially available it will be a useful addition to the armoury  of diagnostic tests for investigating parasitic disease in horses.


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