Do babesiosis and malaria share a common disease process?

Clinical confusion between human babesiosis and malaria is often reported in the literature. Headache, fever, chills, nausea, vomiting, myalgia, altered mental status, disseminated intravascular coagulation, anaemia with dyserythropoiesis, hypotension, respiratory distress, and renal insufficiency are common to both diseases. This remarkable similarity is not restricted to the human host. In the mouse, for example, the histological changes wrought by fatal malaria (Plasmodium vinckei) and babesiosis (Babesia rhodaini) are identical, and parasites of both genera cross-protect. Malarial disease pathogenesis is now generally associated with excessive production of pro-inflammatory cytokines, such as tumour necrosis factor. While this concept has not yet been examined in babesiosis, indirect evidence arises from noting the parasite density at which illness occurs in primary infections caused by either organism. Naive mice tolerate high loads of malarial or babesial parasites before they become ill, and are also tolerant to endotoxicity, which is mediated by these same cytokines. In contrast, humans require very much smaller loads of Plasmodium or Babesia spp. before becoming ill, and likewise are very sensitive to endotoxin, the harmful effects of which are mediated by the pro-inflammatory cytokines. For these reasons, as discussed in this review, the diseases caused by these two genera of intra-erythrocytic protozoan parasites will probably prove to be conceptually identical.