Three-antigen cocktail behind blood test for small strongyles

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Detection of a recently identified antigen in blood is a central element in a new test that can identify small strongyle burdens in horses.

Research that explains the science behind the test for diagnosing infections of small strongyles, also known as small redworms or cyathostomins, has been published in the International Journal of Parasitology.

The paper describes work undertaken to define the final format of the test which was developed at the Moredun Research Institute in Scotland and commercialised by Austin Davis Biologics in September 2019.

A new antigen was discovered to be important in accurately identifying cyathostomin burdens when combined with previously identified cyathostomin antigens in an enzyme linked immunosorbent assay (ELISA) detecting cyathostomin-specific IgG(T) antibodies in horse serum.

An encysted cyathostomin.
An encysted cyathostomin. © Moredun Research Institute

This three-antigen cocktail was identified as being the most suitable for a commercial test to detect all stages of the small redworm life cycle, including the all-important encysted larval phase.

Until now it has not been possible to test for encysted small strongyles as faecal egg counts detect the presence of only egg-laying adult worms.

Small strongyles are the most common gastrointestinal parasites to infect horses.

When horses harbour a large burden of encysted larvae that emerge en masse from the intestinal wall clinical symptoms develop, such as diarrhoea and colic, which can be fatal (larval cyathostominosis).

Moxidectin is the only dewormer capable of eliminating these encysted stages for which worm resistance is not known to be widespread.

To protect the effectiveness of this dewormer, targeted treatment programmes are required to ensure that the drug is administered only when it is really needed.

Blood test results are intended to complete a “diagnostic profile” for veterinarians along with historical faecal egg count results and assessment of grazing management to enable decisions to treat/not treat an individual horse or group.

“This research paper describes the selection of antigens that provide coverage for detecting the commonest cyathostomin species found globally,” says Professor Jacqui Matthews, the chief technology officer at Roslin Technologies and inventor of the test.

The director at Austin Davis Biologics, Dr Corrine Austin, says publication of the research is important as it provides veterinarians with additional evidence of the commercial test’s accuracy.

“Following on from this published research, we conducted additional validation and optimisation of the test for use on robotic systems.”

Dr Stewart Burgess, principal investigator at the Moredun Research Institute, says the availability of the test greatly benefits evidence-based worm control in horses and fills an important gap in the diagnostic toolbox for equine veterinarians.

Tzelos, T., et al (2020). Characterisation of serum IgG(T) responses to potential diagnostic antigens for equine cyathostominosis. International Journal for Parasitology 50, 289–298.

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