A 35-year-old man presents with fever for 14 days, along with fatigue, malaise, generalized arthralgia and myalgia, and a diffuse headache for the same duration. No other symptoms are present. He has been self-medicating himself with acetaminophen and has not sought medical attention thus far.

He returned from a week-long hiking trip in rural Massachusetts around three weeks ago. He does not recall being bitten by insects. The several friends and family who traveled with him are healthy.

There is no contact history with people with similar symptoms. He has a single stable long-term sexual partner. His medical, surgical and family histories are unremarkable. He does not smoke and only drinks socially.

His basic investigations are as follows:

WBC: 5,100/mm3 (4,600-11,00)
Neu: 45% Lym: 37%
Hb: 10.5 g/dL (11-18)
MCV: 90 fL (80-96)
MCH: 30 pg/cell (27-33)
Plt: 196,000/mm3 (150,000-450,000)

ALT: 80 IU/L (7-45)
AST: 72 IU/L (8-48)
Tot. bilirubin: 1.5 mg/dL (0.2-1.2)
Dir. bilirubin: 0.3 mg/dL (0.1-0.4)

Reticulocyte count: 8%
Serum LDH: 800 IU/L (105-333)
Direct antiglobulin test: negative
Indirect antiglobulin test: negative

Renal functions, chest x-rays, and a urinalysis are all normal.

Select Relevant Investigations
Thick + thin blood films


Thick blood films reveal numerous intraerythrocytic parasites.

Thin blood films show reticulocytosis and pear-shaped trophozoites with blue cytoplasm and red chromatin. Multiple ring forms are identified, without hemozoin deposits. Maltese crosses are present. The parasitemia level is 0.3%. No morulae are found in the white blood cells.
Tick-borne disease serology panel


Babesia microti IgM titre: 1:256 (<1:20)
Babesia microti IgG titre: 1:1024 (<1:64)

Negative for Ehrlichia chaffeensis, Anaplasma phagocytophilum, and Lyme disease.
PCR for babesiosis


PCR is positive for Babesia microti.
HIV and hepatitis C screening


Negative for both HIV and Hepatitis C.

Select Relevant Management
Exchange transfusion