Synergic interaction of aromatic compounds thymol and carvacrol against nematode Haemonchus contortus resistant strain

The aim of this work was to evaluate the aromatic compounds thymol and carvacrol and its synergic anthelmintic interactions against sheep gastrointestinal nematode Haemonchus contortus multi resistant strain. Anthelmintic resistance has been a hindrance in animal production causing economic losses and because of the repetitive use of those ineffective chemicals; it is usual to found contamination on meat, milk and environment. New sources of anthelmintic compounds have been investigated. Plant extracts and natural compounds have demonstrated as promising candidates. Eggs were collected from feces of sheep infected with H. contortus according to Bizimenyera et al. [1] technique. A hundred eggs were exposed to solutions of thymol, carvacrol and half and half thymol and carvacrol diluted in water and solvent Tween 80 in concentrations ranging from 2.08 mg/mL to 0.007 mg/mL (decreasing three fold concentrations) with six replicates using a 24 well plate to perform tests. Eggs were incubated for 24h at 27 ° C and the count of eggs hatched was done using an inverted microscope. Data were analyzed by SAS Probit to estimate LC₅₀ with independent variables (dose) transformed by natural logarithm (log dose). The LC₅₀ (fiducial limits) in mg/mL of thymol was 0.13 (0.12 – 0.14), carvacrol was 0.11 (0.10 – 0.12) and the synergic interaction of carvacrol + thymol was 0.037 (0.034 – 0.041). Gas chromatography/mass spectrometry was performed for carvacrol and thymol and 100% and 98% were the similarity with authentic molecules, respectively.

Tab. 1: LC₅₀ (mg/mL) and fiducial limits of Carvacrol, Thymol and Carvacrol + Thymol (50% – 50%) detected by in vitro egg hatch test of gastrointestinal sheep nematode Haemonchus contortus resistant strain.

Aromatic compounds	LC50 (fiducial limits) mg/mL
Carvacrol	0.11 (0.10 – 0.12)
Thymol	0.13 (0.12 – 0.14)
Carvacrol + Thymol	0.037 (0.034 – 0.041)

Acknowledgements: FAPESP proc. 2012/50587 – 5.

Keywords: Essential oil, H. contortus, in vitro, anthelmintic, parasite, sheep, nematode

References:

[1] Bizimenyera, E.S., Githiori, J.B., Eloff, J.N., Swan, G.E., 2006. In vitro activity of Peltophorum africanum sond. (Fabaceae) extracts on the egg hatching and larval development of the parasitic nematode Trichostrontylus colubriformis. Vet Parasitol 2006; 142: 336 – 343.