Infectivity and cross-immunity studies of Theileria lestoquardi and Theileria annulata in sheep and cattle: I. In vivo responses

In a series of experiments, sporozoite stabilates of a Theileria lestoquard i (Lahr) and a T. annulata (Ankara) stock prepared from Hyalomma anatolicum anatolicum ticks, were used to examine the infectivity of both parasite sp ecies for sheep and cattle and to study the development of cross-immunity b etween these parasite species. In the first experiment sheep and cattle wer e inoculated with T. lestoquardi sporozoites. Surviving animals and naive s heep and cattle were, in the second experiment, inoculated with T. annulata , In the third experiment, naive sheep and sheep previously infected with T . annulata, were inoculated with T. lestoquardi. The following responses to inoculations were monitored: clinical and haematological signs of infectio n, appearance of parasitic stages of the parasites in lymph node biopsies a nd in peripheral blood and serological response to T. lestoquardi and T. an nulata schizont antigens. While T. lestoquardi readily infected sheep and c aused severe disease, it did not infect cattle. On the other hand, T. annul ata infected both cattle and sheep. However, whereas cattle became severely affected, infected sheep showed mild clinical symptoms only and piroplasms did not develop. Despite their different behaviour in the host species exa mined, cross-immunity studies suggested that the parasite species are very closely related. Experiments in sheep indicated that T. lestoquardi infecti on protected against subsequent T. annulata infection. On the other hand, r ecovery from T. annulata infection did not prevent infection by sporozoites of T. lestoquardi, resulting in the establishment of schizonts and their s ubsequent development into piroplasms, although it protected against the ma jor clinical effects of T. lestoquardi infection. (C) 1999 Elsevier Science B.V. All rights reserved.