Snapshot A 68-year-old man presents to the physician with complaints of fever, malaise, and chills for the past few weeks. He says that he and his wife recently visited New Hampshire for a summer family reunion, where they hiked in the White Mountains. His temperature is 102°F (38.9°C). Physical exam is notable for a palpable spleen. Laboratory studies are significant for a hematocrit of 30%, decreased serum haptoglobin levels, and an elevated reticulocyte count. A peripheral blood smear is obtained, and confirms the diagnosis. Introduction Epidemiology location northeastern United States (same geography as Lyme disease) risk factors outdoor activities that increase exposure to ticks Pathogenesis transmission Ixodes tick is the vector for the parasite same vector as Borrelia burgdorferi which causes Lyme disease; co-infection may occur white-footed mouse is a reservoir Associated conditions hemolytic anemia Presentation Symptoms fever may be sustained or intermittent chills malaise fatigue arthralgias nausea and vomiting dark urine Physical exam typically few, if any, physical findings in a minority of patients jaundice splenomegaly hepatomegaly petechiae ecchymoses Studies Labs complete blood count with differential mild-to-severe hemolytic anemia lymphopenia thrombocytopenia decreased serum haptoglobin levels elevated reticulocyte counts Histology peripheral blood smear Giemsa-stained or Wright-stained intraerythrocytic ring forms with a central pallor merozoites arranged in tetrad configuration resembling a Maltese cross (pathognomonic of babesiosis) Making the diagnosis based on clinical presentation and peripheral blood smear findings Differential Malaria distinguishing factor visualization of Plasmodium on peripheral blood smear Lyme disease distinguishing factor erythema migrans (bulls-eye rash) Erlichiosis distinguishing factor southeastern and mid-Atlantic United States Treatment Medical IV atovaquone and IV azithromycin IV clindamycinand oralquinine Complications Severe hemolytic anemia Thrombocytopenia Disseminated intravascular coagulation (DIC) Death babesiosis can be severe or life-threatening particularly in the following groups asplenic patients immunocompromised patients elderly