Case Study 6 A one-month-old infant from Massachusetts was fussy, pale, had warm skin, and was vomiting. His temperature was 101.5º F (38.6º C), and he had tachycardia, poor perfusion, splenomegaly, and pulmonary edema.Laboratory studies revealed hemolytic anemia and thrombocytopenia. His ALT was increased, but his other chemistry studies were normal. His urine was dark red and cloudy wi

A one-month-old infant from Massachusetts was fussy, pale, had warm skin, and was vomiting. His temperature was 101.5º F (38.6º C), and he had tachycardia, poor perfusion, splenomegaly, and pulmonary edema.

Laboratory studies revealed hemolytic anemia and thrombocytopenia. His ALT was increased, but his other chemistry studies were normal. His urine was dark red and cloudy with a pH of 7.0, a specific gravity of 1.015, a large amount of blood, 100 mg/dL of protein, and trace leukocyte esterase. The microscopic urinalysis had 0 to 5 red cells and white cells per HPF and 15 to 20 granular casts/LPF. The CSF was normal. The CBC differential slide, shown in the image, was diagnostic.

The newborn's mother visited an island off the coast of Massachusetts recently, where the incidence of this disease is 100 times higher on these islands than on the mainland. The mother had no symptoms. This baby is a twin, but the other twin was not infected. Testing revealed the mother and twin had high titers of antibodies (her titer was 1:4096) to this etiological agent, spread by ticks. What is the diagnosis?