Babesiosis is a tick-borne malaria-like illness caused by species of the intra-erythrocytic protozoan Babesia. Humans are opportunistic hosts for Babesia when bitten by nymph or adult ticks. Currently, Babesia infection is transmitted by various tick vectors in Europe, Asia, Africa and the northwestern and northeastern United States. Human babesiosis was first described in 1957 but is now known to have worldwide distribution. The increase in reported cases is likely due to increases in actual incidence as well as increased awareness of the disease. Despite the diagnostic and preventive advances resulting from extensive research and a greater understanding of the disease, babesiosis continues to have significant medical impact as a confounding variable in the diagnosis and treatment of Lyme disease and as a potential threat to the blood supply, especially in the United States. Diagnostic advances, like the development of PCR assays,
have resulted in increased sensitivity for detection as well as the discovery and characterization of new babesial species. Further studies using the molecular tools now available and those to be developed will lead to a better understanding of the natural history of these organisms, including the transmission cycle and the potential role of Babesia parasites themselves as immunomodulator. Human babesiosis is usually an asymptomatic infection in healthy individuals. Several patients become symptomatic, and, within these subpopulations, significant morbidity and mortality occur, especially in elderly, immunocompromised, or asplenic patients. It is difficult to diagnose. Although the index of suspicion should be high in rural Babesia endemic areas, patients with babesiosis have few, if any, localizing signs to suggest the disease. Diagnosis confirmation depends on the parasitemia degree, the expertise and well trained laboratory personnel. Most patients infected by B microti who are otherwise healthy appear to have a mild illness and typically recover without specific chemotherapy; however, treatment is recommended for all diagnosed cases to prevent sequelae and potential transmission through blood donation. In addition, patients should be advised to take precautions against tick exposure and to refrain from donating blood until completely cured of babesiosis.