The Efficiency of Melatonin in Inhibiting Haemonchus Contortus Development
Haemonchus contortus (HC) is a pathogenic nematode that causes sheep morbidity through anemia, edema, and weight loss. It’s the most economically devastating parasite to sheep industries, with increasing global temperatures and anthelmintic resistance increasing HC residing areas and life spans. HC enter hypobiosis, a state comparable to hibernation during the fall when day length decreases. In this state of arrested development, the sheep are not taxed. Hypobiosis occurs in late fall and early winter. Melatonin, with its release having a direct relationship to length of night, is highest during this period. Combining melatonin’s relationship to the seasons, along with research demonstrating that melatonin can inhibit locomotion in parasites such as Caenorhabditis elegans, it is predicted that melatonin is the cue for HC to enter hypobiosis.
Effects of melatonin levels on development of HC were determined by manually de-worming and inoculating 16 adult Icelandic ewes, followed by twice-daily doses of 5mg of melatonin for three weeks. Fecal samples for HC egg counts, body condition scores (BCS), and FAMACHA scores were taken every three to four days during the experiment. Analysis of P-Tests and T-Tests showed no detectable differences in egg counts, BCS, or FAMACHA scores between the control and treatment group. Our ELISA assays showed that oral administration of melatonin did increase melatonin blood concentrations above control levels. Due to inadequate parasite colonization of ewes during inoculation, we could not adequately test the hypothesis that melatonin inhibits development of HC. Future experiments using more effective parasite inoculation procedures are necessary to adequately test this hypothesis.