Comparative Analysis of Intestinal Helminth Infections in Colic and Non-Colic Control Equine Patients

Simple Summary The most important equine intestinal worm species include the roundworms Strongylus vulgaris and Parascaris spp. as well as tapeworms such as Anoplocephala perfoliata. These parasites reside in the small and large intestine and may cause various signs of disease, such as diarrhea, unthriftiness, or colic. However, following decades of routine anti-worm treatments, it is currently unclear what relevance these infections have in the context of colic under the prevailing situation. Therefore, we examined the signs of the presence of the infection concerning the above-mentioned parasites in 620 equine clinic patients, half of these admitted after being diseased with colic and the other admitted due to non-intestinal diseases. With approximately on third of all horses being positive for antibodies directed against S. vulgaris, we detected an unexpectedly high infection rate. With every tenth horse showing respective antibodies, also tapeworm infections were encountered in a considerable proportion of the examined horses. Somewhat unexpectedly, no association between worm infection and colic was detected. However, recent—i.e., during the last seven days—anthelmintic treatment was 2.4 times more often seen in horses showing signs of colic. Overall, the considerable S. vulgaris and tapeworm infection rates mean we should stay alert in continuing worm monitoring and control. Abstract All around the world, intestinal helminths constitute one of the most prevalent life-long occurring infections and re-infections affecting all horse age groups. A range of parasite species among strongyles, ascarids, and tapeworms is known to have the potential to cause colic in horses. However, there is a lack of current scientific evidence on the actual relevance of helminth infection levels in the context of colic in horses kept during prevailing epidemiological conditions. Thus, a prospective case-control study on the occurrence of intestinal helminths in a total of 620 mainly adult equine clinic patients was conducted to investigate the association between colic and helminth infection. For each horse, a range of copromicroscopic, serological, and clinical data was obtained, in addition to a questionnaire on relevant anamnestic data, including previous anthelmintic treatment and husbandry. Using a FLOTAC-based copromicroscopic diagnosis, the highest infection rates were seen for strongyles (41.8%), followed by Anoplocephala perfoliata and Parascaris spp. (both 0.8%), with no significant difference between the two study groups. Employing a real-time PCR a 1.1% S. vulgaris DNA prevalence was found. Considerably higher seroprevalences were observed using S. vulgaris and A. perfoliata ELISAs, with 32.3% and 10.7%, respectively. It was noteworthy that no association concerning either serologic status was encountered with colic status. The shedding of strongyle eggs was associated with a 1.8-times increased risk of S. vulgaris seropositivity. Recent anthelmintic treatment was associated with the onset of colic, as animals who had received an anthelmintic during the previous week had a 2.4-times higher risk of signs of colic compared to those who had been treated at least eight weeks prior. Another noteworthy observation was that ponies were significantly less often affected by colic than warmbloods. The high S. vulgaris and considerable A. perfoliata seroprevalences encountered in this investigation should prompt veterinarians, farm managers, and horse owners to maintain consequent and effective worm control measures.