Efficacy of Fenbendazole and Ivermectin against Trichuris spp. in African Green Monkeys (Chlorocebus sabaeus) in Barbados West Indies |
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Authors: | Kamara JR Rhynd Daniel P Walsh Linnell CM Arthur-Banfield |
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Affiliation: | 1.Barbados Primate Research Center, Barbados, West Indies, and;2.National Wildlife Health Center, US Geological Survey, Madison, Wisconsin |
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Abstract: | 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.Trichuris spp. (whipworms) from the family Trichuridae are common soil-transmitted gastrointestinal nematodes with a worldwide distribution in mammals.7 Trichuris trichiura is the whipworm species that commonly infects humans and NHP,18 but morphologic and biometrical studies have yielded results suggesting that other Trichuris species may also be present in NHP.6,11,53Trichuris spp. have a direct life cycle, with eggs transmitted via the fecal–oral route with infection occurring from ingestion of embryonated eggs in contaminated food, soil, and water.48 Under optimal environmental conditions, Trichuris spp. eggs can remain viable in infected soil for years.23 After ingestion, the released L1 larvae molt and travel to the cecum and colon, where they bury into the epithelia and develop into adults. After mating, the unembryonated eggs are released from the female and are deposited into the environment in the host feces.7,13 Light infection is asymptomatic; however severe infection produces clinical signs such as severe enteritis, anorexia, gray mucoid diarrhea, and sometimes death.5The prevalence of Trichuris spp. (whipworms) in NHP usually is high,49 and species in this genus are commonly found in Old World NHP, including African green monkeys (AGM), baboons, macaques, and sykes.39,54 High prevalence rates ranging from 60% to 98% have been recorded in wild populations,30,39,42 and prevalence rates ranging from 30% to 79% have been found in captive colonies of NHP in zoological parks and research facilities.1,26,39,50 In the Caribbean, a study of captive AGM in St Kitts54 revealed a prevalence of 91%, whereas 53% was recorded in recently captured wild AGM in Barbados.40AGM (Chlorocebus sabaeus) are the only wild NHP species found on the island of Barbados. These animals were introduced into the island soon after it was colonized in 1627.3 Populations are also found on the islands of St Kitts-Nevis, St Maarten/Martin, and Tortola.14 AGM are used widely in biomedical research25 for studies on hypertension,15 neurologic disease20,34 and vaccine production.36,52 In a research setting, NHP should be parasite-free24 for the sake of the animal’s health (which in turn affects research outcomes) and to eliminate possible risk of transfer of zoonoses to caregivers and other research facility personnel.Different classes of drugs have been used to treat Trichuris spp. infection in NHP, including benzimidazoles like fenbendazole, mebendazole, and albendazole,45,46,55 and avermectins.27,51 Studies have been conducted using these drugs in macaques, vervets, baboons, and langurs.21,27,38,44,51 Fenbendazole and ivermectin have been used at various doses in the treatment of Trichuris infection in NHP. Fenbendazole has been administered at doses of 10 to 50 mg/kg PO daily for 3 to 5 d, with or without repeated doses.16,38,44,45 Ivermectin has been administered at doses of 100 to 400 µg SC, IM, or PO as a single dose or at specified intervals.21,24,38,51 Little published data exist regarding the use of these drugs specifically in AGM. The current study was conducted to compare the efficacy of fenbendazole and ivermectin—alone and in combination—against Trichuris spp. in naturally infected AGM in Barbados, West Indies, for clearance of this parasite. |
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