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, 11, 183-190

Not Playing by the Rules: Unusual Patterns in the Epidemiology of Parasites in a Natural Population of Feral Horses ( Equus caballus) on Sable Island, Canada


Not Playing by the Rules: Unusual Patterns in the Epidemiology of Parasites in a Natural Population of Feral Horses ( Equus caballus) on Sable Island, Canada

Emily Jenkins et al. Int J Parasitol Parasites Wildl.


Sable Island, Nova Scotia, Canada hosts one of few natural populations of feral horses (Equus caballus) never exposed to anthelmintics. Coproculture revealed cyathostomes, Strongylus equinus, S. edentatus, and S. vulgaris, with S. equinus (unusually) dominating in adult horses and cyathostomes dominating in young horses (<3 years of age). We examined 35 horses found dead in the springs of 2017 and 2018, as well as fecal samples from live horses in spring (n = 45) and summer 2018 (n = 236) using McMaster fecal flotation and Baermann larval sedimentation on fresh samples, and modified Wisconsin flotation and sucrose gradient immunofluorescent assay for Giardia and Cryptosporidium on frozen samples. Mean strongyle fecal egg counts were 666 eggs per gram (EPG) in dead horses, 689 EPG in live horses in spring, and 1105 EPG in summer; domestic horses are usually treated at counts exceeding 200 EPG. Adult horses (unusually) had patent infections with the lungworm Dictyocaulus arnfieldi and ascarids (Parascaris spp.), and in spring, dead horses had 5 times higher odds of having patent ascarid infections than live horses, likely due to malnutrition and corresponding immunodeficiency. Fecal prevalence and intensity of D. arnfieldi and Parascaris spp. were significantly higher in young horses, and in spring versus summer. A higher proportion of fecal samples were positive for strongyle and ascarid eggs using a centrifugal flotation technique on previously frozen feces, as compared to a passive flotation method on fresh feces. Eggs of the tapeworm Paranoplocephala mamillana were present in fecal samples from 28% of live, and 42% of dead, horses in spring. This research represents several new geographic records (S. edentatus, D. arnfieldi, and Eimeria leuckarti), provides insight into unusual patterns of parasite epidemiology in a nutrition-limited environment, and has conservation and biosecurity implications for this unique equine population, as well as for parasite management in domestic horses.

Keywords: Ascarid; Feral horse; Intensity; Large strongyle; Lungworm; Prevalence.


Image 1
Fig. 1
Fig. 1
Map of Sable Island, Canada, which is about 50 km long, 1 km wide at its widest point, and in total, 34 km2 (from Gold et al., 2019).
Fig. 2
Fig. 2
a) Dictyocaulus arnfieldi first-stage larvae showing typical granular appearance and beginning of cuticular separation b) closer view of tail showing stylet, or spear.
Fig. 3
Fig. 3
Proportions of third-stage larvae of large and small strongyle species cultured from feces of 81 Sable Island horses in summer 2014, showing an unusual dominance of S. equinus in adult horses. Larvae with a rhabditiform pharynx were rare in young (1–3 years) and adult horses (≥3 years), but common in foals, which could represent larvae of Strongyloides westeri.

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