Eimeria spp.can infect poultry and livestock and causes coccidiosis.The estimate of annual economic losses due to chicken coccidiosis is 3 billion US dollar in the global poultry industry.Therefore,understanding the relationship between eimerian parasites and host cells,such as egress,is of great interest for the development of coccidiosis control strategies.In this study,we observed the effect of acetaldehyde,a reagent which is able to elevate intracellular Ca2+ in a variety of vertebrate cells,on the induction of egress of Eimeria tenella sporozoites from in vitro cultured primary chicken kidney cells.We found that acetaldehyde could induce egress of the sporozoites and stimulate the secretion of E.tenella microneme 2 protein which is related to the mobility of the parasite.Moreover,these processes were proved to be dependent on the intraeellular calcium(Ca2+)of the parasites.Taken together,our findings provide a new approach to study the relationship between Eimeria parasites and their vertebrate hosts.