A case study on Toxascaris leonine in big felids: inessicacy of a single-dose treatment with pyrantel pamoate

Elimination of helminthiasis from zoological collections is a challenging issue and often the eradication of the infection is not completely and definitely achieved. Maintenance of ascaridiosis in a facility is helped by the great resistance of the parasite's eggs, the wide host spectrum and a non-strictly monoxenous life cycle. In this case study, copromicroscopic examinations carried out in a facility hosting large felids in Northeastern Italy showed that 14/29 animals were positive for Toxascaris leonina. Following AZA manual recommendations, all positive animals were treated with pyrantel pamoate at 5 mg/kg PO for one or three consecutive days depending on the species and the efficacy of the treatment was proved by the complete absence of eggs in stool samples after 10 days. Nevertheless, faecal egg shedding reoccurred after 60 days, an insufficient period for the development of reinfection from environmental contamination. We hypothesize that two consequential treatments with Pyrantel pamoate are thus to be considered essential to eliminate larval stages of the parasite lodging in the gut walls. These larvae could indeed give origin to new patent infection after 60 days, making the single treatment ineffective in reducing the parasitic environmental burden.