Improved techniques for the in vitro cultivation of Eimeria tenella in primary chick kidney cells

Primary kidney cells of 1- to 4-week-old chickens (PCKC) grown in Flexiperm chambers or culture flasks were infected with ultrapure sporozoites of two Eimeria tenella strains. For the 24-h parasite-free adaptation phase of the PCKC culture, Williams E medium plus 10% foetal calf serum (FCS) was used, and for the subsequent parasite-containing 168-h maintenance phase, we used medium 199 plus 2.5% FCS. Monolayers established during that time enabled the routine development of all schizont generations as well as, in general, young oocysts. The parasite stages propagated in FLEX were rendered visible by modified PAS-AO staining. Sporulated oocytes differed in length and width from those recovered after their passage through chickens. These results show that E. tenella can reliably be reproduced from sporozoites to oocysts in PCKC cultures. However, the yield of oocysts was generally low, indicating that mass production of oocysts is achieved only by passaging sporulated oocysts through chickens.