A 43-year-old man presented as a referral for bilateral central vision loss. His medical history was significant for Crohn disease controlled with monthly injections of ustekinumab (Stelara; Janssen Biotech Inc). Symptoms of fever, headache, and myalgia began 1 week prior following a tick bite. He was prescribed oral doxycycline hyclate for suspected Lyme disease. Owing to persistent fever while receiving oral doxycycline hyclate, he was admitted for intravenous administration of doxycycline hyclate, and the fever resolved. He was found to be anemic (hemoglobin concentration, 6.7 g/dL; normal concentration, 13.5-17.5 g/dL) (to convert hemoglobin concentration to g/L, multiply by 10), requiring transfusion. While hospitalized, he developed acute bilateral central scotoma. Magnetic resonance imaging of the orbit and brain with and without contrast was unremarkable. Infectious serology test results for Lyme disease, syphilis, malaria, Anaplasma species, Cryptococcus species, Rocky Mountain spotted fever, and rickettsia were negative. Rheumatologic serology test results for antinuclear antibodies, including Sjögren anti-Ro and anti-La, anti-DNA, and anti-Smith, were also negative. Antineutrophil cytoplasmic antibody testing revealed elevated proteinase 3 antibody level. In the setting of anemia, infectious-disease consultants raised concern for babesiosis. Peripheral blood smear and polymerase chain reaction were performed; empirical therapy of azithromycin, 500 mg daily, plus atovaquone, 750 mg twice daily, was initiated. Polymerase chain reaction results for babesiosis later returned as negative.