Abstract:
The published literature on schizont-“transforming,” or pathogenic theileriosis, in African wild artiodactyls is dated and based on
limited information. Here the authors review the taxonomy, diagnosis, epidemiology, hematology, pathology, and aspects of
control in various species. Molecular studies based on 18S and 16S rRNA gene sequences have shown that African wild artiodactyls
are commonly infected with diverse Theileria spp., as well as nontheilerial hemoprotozoa and rickettsia-like bacteria, and
coinfections with pathogenic and nonpathogenic Theileria species are often recorded. Although theileriosis is still confusingly
referred to as cytauxzoonosis in many species, the validity of a separate Cytauxzoon genus in artiodactyls is debated. The epidemiology
of theileriosis is complex; the likelihood of fatal disease depends on the interplay of parasite, vertebrate host, tick
vector, and environmental factors. Roan calves (Hippotragus equinus) and stressed animals of all host species are more susceptible
to fatal theileriosis. Even though regenerative anemia is common, peripheral blood piroplasm parasitemia does not correlate with
disease severity. Other than anemia, common macroscopic lesions include icterus, hemorrhages (mucosal, serosal, and tissue),
fluid effusions into body cavities, lung edema, and variably sized raised cream-colored foci of leukocyte infiltration in multiple
organs. Histopathologic findings include vasocentric hyperproliferation and lysis of atypical leukocytes with associated intracellular
schizonts, parenchymal necrosis, hemorrhage, thromboembolism, and edema. Immunophenotyping is required to establish
the identity of the schizont-transformed leukocytes in wild ungulates. Throughout the review, we propose avenues for future
research by comparing existing knowledge on selected aspects of theileriosis in domestic livestock with that in African wild
artiodactyls.
