Evidence‐based considerations for control of Parascaris spp. infections in horses

Abstract

Summary Parascaris spp. infection is virtually ubiquitous in young foals and worm burdens can achieve high numbers. The most important disease manifestation is impaction of the small intestine, which occurs in a small proportion of infected foals but is associated with a guarded prognosis for survival. Control of Parascaris spp. is complicated by emerging resistance to currently available anthelmintic drug classes. Resistance to macrocyclic lactones has been reported worldwide and a few studies have also documented signs of resistance to pyrantel salts and benzimidazoles. Foals generally develop immunity to Parascaris spp. parasites around age 6 months, but a proportion of weanlings and yearlings can harbour smaller burdens at age 8–10 months. Older horses have occasionally been reported with substantial ascarid burdens as well. Qualitative detection of ascarid eggs has good diagnostic value whereas an actual egg count does not correlate well with the size of the worm burden. A recent investigation documented the applicability of a transabdominal ultrasound technique for semiquantitatively monitoring ascarid burdens in foals. Control of ascarids is complicated by the limited drug classes available for treating this parasite, and by the fact that foals are often concurrently infected with strongyles. In many cases, none of the 3 available anthelmintic classes are simultaneously effective against both parasite groups, so close monitoring is required to select the most appropriate anthelmintic in each case.

Efficacy of a morantel–abamectin combination for the treatment of resistant ascarids in foals

“…Coprophagy is a normal behaviour in foals and is another potential influence on the FECR testing in this study. However, the prevalence of false‐positive Parascaris FECs in foal faeces is low and unlikely to have affected the FECRT results.…”

A survey of ivermectin resistance in Parascaris species infected foals in south-eastern Poland

“…This infection can lead to respiratory symptoms, poor growth, ill thrift accompanied by rough hair coat and bouts of diarrhoea or colic. In some cases, ascarids can lead to an obstruction and rupture of the small intestine or death of foals [2][3][4]. In Poland, ivermectin is the most widely used anthelmintic in equine parasite treatment [5,6].…”

“…from individual horses. We followed the guidelines of the American Association of Equine Practitioners [3] providing percent reduction thresholds for diagnosing drug resistance in strongyle populations. In general, a percent efficacy of < 95% for the macrocyclic lactones indicates resistance while a level of 95-98% is interpreted as suspected resistance.…”

Control of helminth parasites in juvenile horses

“…Hygienic measures to decrease exposure to infective eggs from pastures, paddocks and stalls should reduce the magnitude of Parascaris spp. worm burdens, but virtually nothing is known about the quantitative efficacies of the various procedures (reviewed by Nielsen ). Regular cleaning and disinfection of stalls used for foals and mares every year could be beneficial, but the scientific literature offers little guidance regarding the ability of various disinfectants to remove or inactivate ascarid eggs from contaminated premises.…”