Cryptosporidium and Giardia spp. are small coccidian parasites that infect the intestinal tract of birds, reptiles and mammals including humans. Oocysts of Cryptosporidium parvum and cysts of Giardia duodenalis are shed in the feces of infected animals and directly infect subsequent hosts following ingestion. The broad host range, resistant nature, and small size of the parasites in the environment may potentially contribute to contamination of water supplies. The perception that recreational riding horses may increase the prevalence of Cryptosporidium and Giardia in large watersheds adjacent to common trails, indirectly infecting humans, has resulted in banning recreational riding horses from some trails. However, there is currently no scientific data linking the recreational trail horse to the incidence or increased risk of human cryptosporidiosis or giardiasis. This survey was conducted to determine the prevalence of Cryptosporidium and Giardia spp. in recreational horses utilizing trails located near large watershed areas in Colorado. At the trail heads, approximately 10 g of fresh feces were collected from recreational horses (n=300) that were utilizing the trails on the day they were sampled. Fecal samples were mixed with 10% formalin at a dilution rate of 1 part feces to 4 parts formalin and were transported to the Veterinary Diagnostic Laboratory at Colorado State University. Samples were evaluated using the Merifluor™ Cryptosporidium/Giardia Direct Immunofluorescent Detection Procedure. One horse (0.33%) was detected positive for Cryptosporidiurn and two horses (0.66%) were positive for Giardia. The low prevalence of Cryptosporidia and Giardia in the trail horse population surveyed indicates that the adult recreational trail horse population is not likely to be a significant source of Cryptosporidium and Giardia environmental contamination in watershed areas.
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