Research published in Equine Veterinary Journal shows testing for tapeworms using the commercially available EquiSal® test and treating only the horses affected, significantly reduces the use of anti-tapeworm treatments and, therefore, will reduce selection pressure for tapeworm resistance to anthelmitic drugs in the future.
The development of drug resistance in horse parasites and, particularly, redworms (cyathostomes) is of concern because of the limited treatment options that exist and has prompted a change in the approach to controlling worms in horses. The current recommendation is to diagnose and treat only those individuals whose worm burden is above a set threshold.
Faecal egg counts are valuable in detecting the presence of some of the common adult parasites, but they do not inform of tapeworm infection. There is, however, a less-known, commercially available saliva-based test (EquiSal®) that has been shown to accurately diagnose the presence of tapeworm in horses.
While tapeworm resistance to anthelmitic drugs has not yet been identified, veterinarians are mindful a reduction in use of these medications is essential, so they devised a study to check if using the available saliva test could help manage tapeworm infection, while reducing the use of treatment drugs.
The researchers collected saliva from 237 horses at a United Kingfom welfare charity three times during a period of one year (Autumn 2015, Spring 2016 and Autumn 2016). Using the EquiSal® test, horses that were diagnosed as having a borderline or moderate/high burden of tapeworm infection were treated with an anti-tapeworm drug, according to their weight. Horses that tested below threshold were not treated.
Horses that arrived at the charity after the testing period had started were also tested and the information was used to inform quarantine treatments.
At the start of the testing period (Autumn 2015), 202 of the 237 horses (85%) tested negative and did not receive the first treatment. Of those, the majority (184 or 71%) remained below the treatment threshold throughout the study and, therefore, did not receive any treatment.
Despite being below threshold in Autumn 2015, 15 horses required treatment in Spring 2016. Of the 35 that had received the first treatment in Autumn 2015, only 16 required the second treatment.
In Autumn 2016, on the third test, 204 horses tested negative and required no treatment. And of the 33 horses that received treatment, 19 horses had received no prior treatment, seven horses had been treated either in Autumn 2015 or Spring 2016, and another seven horses had been treated in both previous tests.
Overall, 168 horses (71%) remained below the test threshold throughout the study and a total of just 69 horses required treatment. Of these, only seven horses required treatment following all three tests.
Over 50% of the horses treated fell below the threshold at the following test and, most importantly, there was no increase in tapeworm prevalence during the study, despite the substantial reduction in the use of anti-tapeworm treatments when compared to a ‘blanket treatment’ strategy of worming all horses.
The researchers conclude their study has provided a sound basis for targeted control of tapeworm infections within horse herds. Six-monthly testing for tapeworm adequately identifies horses at an early stage of infection, allowing owners to provide early treatment and avoiding paddock contamination. It will also identify those horses that are more prone to tapeworm infection.
Most importantly, testing for tapeworms and treating only the horses affected will reduce the use of anti-tapeworm treatments, and reduce selection pressure for resistance in the future. They added future research should take into account other parasite management strategies to further reduce anthelmitic use.
A video abstract is available here: https://vimeo.com/254338616
The study “Use of a saliva-