Efficacy of fenbendazole and ivermectin against Trichuris spp. in African green monkeys (Chlorocebus sabaeus) in Barbados West Indies

Trichuris spp. are common helminths in NHP, and benzimidazoles and avermectins have both been used to treat these intestinal parasites. The current study compared the efficacy of fenbendazole and ivermectin against natural infection of Trichuris spp. in African green monkeys (Chlorocebus sabaeus). Anthelmintic-naive animals (n = 65) were randomly assigned to 4 groups: an untreated control group, and 3 groups treated with either fenbendazole, ivermectin, or both compounds. Fecal samples were collected before treatment and on days 7, 14, 28, and 60 after treatment, and fecal egg counts (FEC) were determined by using fecal flotation. The mean percentages of FEC reduction at day 60 were 100%, 86%, and 100% for treatment with fenbendazole, ivermectin, and both compounds, respectively. Analyzing the time series of FEC by using a Bayesian generalized linear model showed no significant difference in the proportional reduction in FEC among the 3 treatment groups, although all FEC from treated groups were significantly lower than the FEC of the control group. In contrast, the probability of shedding was highest in the ivermectin group and the lowest in the animals treated with both compounds. The probability of shedding differed significantly between the fenbendazole and ivermectin groups and between the ivermectin and combined-treatment groups. In conclusion, both fenbendazole and ivermectin are effective anthelmintics in treating Trichuris spp. infection in African green monkeys. All treatment groups showed significant reductions in FEC when compared with baseline counts and control animals; however, fenbendazole may be more effective than ivermectin when used solely or in combination with other anthelmintic treatments.