Antibody-based tests crucial to sustainable control of horse parasites – review

Antibody-based tests represent an important way forward in the fight against parasitic worms in horses, according to the authors of a just-published review.

These tests, which measure parasite-specific antibodies, have already been developed for cyathostomins (small strongyles) and Anoplocephala perfoliata — the most common intestinal tapeworms in horses.

“These have been used in the United Kingdom and Europe to support veterinarians in making treatment decisions where fecal egg count testing is of limited value,” Jacqueline Matthews, Natalia Peczak and Kirsty Lightbody wrote in the journal Pathogens.

“Use of these tests has led to substantial reductions in anthelmintic applications compared to levels used in traditional interval treatment approaches.”

Such reductions should result in lower selection pressure for resistance to dewormers, thus prolonging the longevity of these important medicines, they said.

The trio, with Austin Davis Biologics Ltd in England, said similar tests need to be made available for pathogens such as Strongylus vulgaris (commonly known as large strongyles or blood worms) to enable monitoring of the impact of reduced dewormer use to avoid undesirable consequences.

Their paper, which cites 112 published studies, reviews the development, performance and general usefulness of various diagnostic methods available that can help with parasite management decisions in horses.

Parasitic worms are commonly found in grazing equids, with cyathostomins and A. perfoliata being most prevalent.

“Most horses harbour low burdens of these parasites and do not develop signs of infection,” they said.

However, in a small number of animals, high burdens can accumulate and cause disease. Cyathostomins are associated with a syndrome known as larval cyathostominosis. This occurs when large numbers of larvae emerge from the large intestinal wall. It has a case fatality rate of up to 50%.

A. perfoliata infection has been associated with various types of colic, with burdens of more than 20 worms associated with pathogenicity (likely to cause disease), they said.

Resistance is a serious problem in cyathostomins and is emerging in A. perfoliata, the review team said.

“Control methods that reduce reliance on anthelmintics now need to be applied, especially as no new dewormer compounds are on the horizon.

“Sustainable control methods must employ diagnostics to identify horses that require treatment.”

Faecal egg counts have been used for several decades to inform treatment decisions to reduce parasite egg shedding.

“These tests cannot be used to assess host burdens as faecal egg counts do not correlate with cyathostomin or A. perfoliata burdens.”

However, in the last decade, new tests have become available that measure parasite-specific antibodies, the levels of which have been shown to correlate with parasite burdens.

These tests measure antigen-specific IgG(T) and are available for serum testing for small strongyles and A. perfoliata, and a saliva test is also available for A. perfoliata.

Tests for other parasites have been developed as research tools and need to be translated to support equine clinicians in practice, they said.

“A key element of sustainable control strategies is that diagnostics must be used in combination with management approaches to reduce environmental transmission of helminths,” they said.

“This will help limit the proportion of horses harbouring parasite burdens that need to be targeted by treatment.”

Matthews, J.B.; Peczak, N.; Lightbody, K.L. The Use of Innovative Diagnostics to Inform Sustainable Control of Equine Helminth Infections. Pathogens 2023, 12, 1233. https://doi.org/10.3390/pathogens12101233

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