Microbiology Case Study: A 50 Year Old Male with Fevers

Case History

The patient is a 50 year old male who presented to urgent care with 5 days of fevers, chills, and myalgias. He reports no known tick bites, or prior treatment for tickborne illness, he travels frequently for work and has been in Pittsburgh, Omaha, Philadelphia, Charlotte, and Long Island over the past 3 months and is frequently outside golfing in Vermont and while traveling. At urgent care he had a CBC, CMP and urinalysis. His CBC was remarkable for leukopenia with absolute neutropenia (WBC count 2,790; Absolute neutrophil count 390) and thrombocytopenia (platelet count 26,000/cmm). His CMP was remarkable for a mildly elevated AST (66U/L) and total bilirubin (2.4mg/dL). A peripheral blood smear was made which revealed ring forms in his red blood cells. BINAX testing for malaria was negative. The next day he presented to the emergency department with left upper quadrant abdominal pain, night sweats, fatigue, fever, and blood in his urine where is was informed of his CBC results and was immediately started on azithromycin and atovaquone. Given the severity of his presentation a co-infection with Anaplasma phagocytophilum (Anaplasmosis) was suspected though the PCR testing was negative.

Laboratory Identification

Image 1. Giemsa stain of thin blood smears showing intracellular (left) and extracellular (right) ring-form organisms.

Thick and thin blood smears (recommended) were prepared which showed both intra and extracellular organisms with in normal sized red blood cells. BINAX testing for malaria was negative. Given the appearance and presence both within and outside the cell a diagnosis of Babesiosis was made.


Babesiosis in the United States is caused by the microscopic parasite Babesia microti. Occasional cases caused by other species of Babesia have been detected (1). Babesia microti is spread by Ixodes scapularis ticks (also called blacklegged ticks or deer ticks) (1,2). Transmission mainly occurs in parts of the Northeast and upper Midwest; and it usually peaks during the warm months (1). Because Babesia shares a vector and geographic distribution with Borrelia burgdorferi (Lyme disease) coinfection of ticks with these two organisms can be seen in up to 40% of ticks and though the incidence of Babesiosis is much lower; up to 10% of Connecticut patients with seropositivity for Lyme disease are also seropositive for Babesia (2).

Most infections are probably asymptomatic. Manifestations of disease include fever, chills, sweating, myalgias, fatigue, hepatosplenomegaly, and hemolytic anemia. Symptoms typically occur after an incubation period of 1 to 4 weeks, and can last several weeks. The disease is more severe in patients who are immunosuppressed, splenectomized, and/or elderly (1,3).

During a blood meal, a Babesia-infected tick introduces sporozoites into the human host (1,3). Sporozoites enter erythrocytes and undergo asexual replication (budding). Multiplication of the blood stage parasites is responsible for the clinical manifestations of the disease (1). Humans are dead-end hosts and there is probably little, if any, subsequent transmission that occurs from ticks feeding on infected persons (1). However, human to human transmission is well recognized to occur through blood transfusions (1). Diagnosis is often rendered by direct visualization on thick and thin blood smears. Because the percent parasitemia is often low, the organisms can be easily missed, especially by automated hematology analyzers (3). Molecular methods such as PCR can be performed (3), but are not recommended as the first line test as the blood parasite exam with thick and thin blood smears are clinically sensitive in patients with symptomatic disease.

Most mild cases of Babesiosis will resolve spontaneously without treatment, especially in patient with a spleen (1,3). Treatment for more severe disease includes either azithromycin and atovaquone or clindamycin and quinine (1,3). If patients are severely immunocompromised and/or splenectomized can be treated with exchange transfusion in addition to antimicrobials (3).


  1. Centers of Disease Control and Prevention: Babesiosis. https://www.cdc.gov/parasites/babesiosis/
  2. Procop, Gary W., et al. Konemans Color Atlas and Textbook of Diagnostic Microbiology. 7th ed., Wolters Kluwer Health, 2017.
  3. Tille, Patricia M. Bailey & Scotts Diagnostic Microbiology. 13th ed., Elsevier, 2014.

-Casey Rankins, DO, is a 3rd year Anatomic and Clinical Pathology resident at the University of Vermont Medical Center.

-Christi Wojewoda, MD, is the Director of Clinical Microbiology at the University of Vermont Medical Center and an Associate Professor at the University of Vermont.

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