Efficacy of an orange oil emulsion as an anthelmintic against Haemonchus contortus in gerbils (Meriones unguiculatus) and in sheep

Haemonchus contortus is a blood-sucking abomasal parasite responsible for major losses to small ruminant producers worldwide. The recent increase in populations of anthelmintic resistant parasites has produced a demand for alternative control methods. An orange oil emulsion that has shown activity against plant parasitic nematodes and H. contortus in vitro was assessed for activity against H. contortus in a gerbil model and in the natural ovine host. In gerbil experiments, animals were infected with 600 infective third stage (L3) H. contortus larvae. In one experiment, gerbils were treated with 600 milligrams per kilogram bodyweight (mg/kg BW) orange oil once or daily for 5 days. In a second experiment, gerbils were treated with 1200 mg/kg BW orange oil once or daily for 5 days. On Day 9 post-infection, gerbils were killed, their stomachs removed, and the worms counted. The 600 mg/kg BW dosage caused 7% and 62.6% parasite reduction compared to a control group when given once or daily for 5 days, respectively. The 1200 mg/kg BW dosage of orange oil caused 25% and 87.8% parasite reduction compared to a control group when given once or daily for 5 days, respectively. The difference between the multiple treatment and control group were significant at both dosages (P < 0.005). In the sheep trial, 18 lambs were orally inoculated with 10,000 L3 H. contortus. One month later, two groups of six lambs each were dosed with 600 mg/kg BW orange oil either once or daily for 3 days. Fecal egg counts were monitored daily starting on the first day of treatment (Day 0) and continuing for 14 days. Results showed that a single dose of the product caused high fecal egg count reduction (97.4%) compared to control sheep. Egg counts were significantly reduced by Day 2 (P < 0.0001). Thus, the orange oil emulsion may potentially be useful in the control of ovine haemonchosis.