Infectivity and cross-immunity studies of Theileria lestoquardi and Theileria annulata in sheep and cattle - II. In vitro studies

In the studies previously reported, the tick-borne protozoan parasites Thei leria lestoquardi and Theileria annulata were shown to differ in their capa city to infect sheep and cattle. In the studies presented here, these findi ngs were further supported. In vitro infectivity of T. lestoquardi and T. a nnulata sporozoites for peripheral blood mononuclear cells of sheep and cat tle were determined by analysis of cell cultures for cell proliferation, th e detection of parasites in Giemsa-stained cytospin smears and the establis hment of continuously growing schizont-infected cell lines. In the same way , the development of schizont-infected cells into continuously growing cell Lines was studied with material isolated ex vivo from the sheep and cattle undergoing primary infections described elsewhere. Comparisons were also m ade between development of ex vivo cell Lines from animals undergoing prima ry infections with those of the animals undergoing challenge infection with the other parasite species. Theileria species specific primers were used i n a PCR to determine the identity of the parasites in the cell lines. These in vitro studies confirmed earlier observations that T. lestoquardi was un able to infect cattle, whereas infection of all sheep with T. annulata was proven. Moreover, earlier indications of the development of partial cross-i mmunity in sheep of T. annulata to T. lestoquardi and vice versa were stren gthened. These findings may thus have consequences for the understanding of the epidemiology of T. lestoquardi infections of sheep. On the other hand, since piroplasms were not demonstrated in sheep infected with T. annulata, such sheep will not be infective to ticks and will consequently be unlikel y to play a role in the maintenance and transmission of T. annulata to catt le. (C) 1999 Elsevier Science B.V. All rights reserved.