Theileria annulata, the causative agent of tropical theileriosis, is a protozoan parasite that also causes lymphoproliferative
diseases in cattle. In vivo, parasitized cells undergo clonal expansion and infiltrate both
the lymphoid and non-lymphoid tissues of the infected host. To determine whether the small ruminants
and their red blood cells (RBCs) were invaded by T. annulata schizonts or not, T. annulata schizonts were
used to infect bovine, ovine and caprine RBCs in vitro, and sheep and goats in vivo. The results showed
that the schizonts infected bovine, ovine and caprine RBCs in vitro, but not sheep and goats, which
showed only an increase in body temperature and no development of piroplasms. To our knowledge, this
is the first report of infection of small ruminants and their RBCs by T. annulata schizonts.