Resistance to
coccidiostats and possible future restrictions on their use raise the need for alternative methods of reducing
coccidiosis in poultry. The aim of this study was to evaluate the effect of selected
phytochemicals on Eimeria tenella sporozoite invasion in vitro. Four
phytochemicals were selected on the basis that they reduce the virulence of Eimeria spp. and/or provide immune modulatory benefits to host cells:
betaine,
carvacrol,
curcumin and
Echinacea purpurea extract (EP). Madin-Darby bovine kidney (MDBK) cells were covered by medium containing
phytochemicals at the highest concentration which was non-toxic to the cells.
Salinomycin 50 μg/ml was positive control; negative control was medium only. E. tenella (Houghton strain) sporozoites were added to wells and after incubation for 2, 4 or 20 h at 37°C, cells were fixed and stained with
hematoxylin-
eosin. Ten evenly spaced fields per well were photographed and the percentage of cells invaded by sporozoites was calculated and normalized to the control. At 2h,
carvacrol,
curcumin and EP showed a significantly lower percentage of sporozoite invasion than the untreated control; in contrast,
betaine treatment represented a significantly higher invasion percentage. Combining
carvacrol with EP inhibited E. tenella invasion more effectively than applying the compounds individually, but the further addition of
curcumin did not reduce invasion further. In conclusion, this study shows that invasion of MDBK epithelial cells by E. tenella sporozoites is inhibited in the presence of
carvacrol,
curcumin, or EP and enhanced by
betaine. There may be potential for developing these
phytochemicals as anti-coccidial feed or water additives for poultry.