Strongyloides westeri worm and egg counts in naturally infected young horses

Strongyloides westeri is a threadworm parasite found in the small intestine mainly in foals at up to about 4 months of age. This parasite is associated with small intestinal enteritis and diarrhea as well as skin irritation and a clinical syndrome called “frenzied behavior” due to percutaneous invasion. The aim of this study was to investigate S. westeri parasite burdens in age groups older than the initial lactogenic transmission phase. Secondary aims were to examine the impact of host age and gender on worm burden and egg output in naturally infected foals. Thirteen foals were enrolled in the study, exposed to natural infection with S. westeri and were humanely euthanized at ages ranging from 89 to 221 days old. Egg counts per gram of feces were determined using the Mini-FLOTAC method. Worms were retrieved from the mucosa of the anterior half of the small intestine using a digestion method and enumerated. The foals were all observed to be healthy with no signs of parasitic disease. Foals at 4–5 months of age had significantly higher S. westeri worm and egg counts compared to those aged 6–8 months (p < 0.05). Fecal egg counts were significantly associated with worm counts (p = 0.0045). While egg and worm counts declined markedly in the 6–8 month age range, they were not eliminated completely. This could either reflect a new infection acquired orally or transcutaneously, or a subset of adult intestinal parasites acquired via the lactogenic route and surviving for longer time periods. This study provided new information about S. westeri infection patterns in young horses at 4–8 months of age.