Neutropenia in Congenital and Adult Babesiosis

Gary P. Wormser, MD; Patrick Villafuerte, MD; Sheila M. Nolan, MD, MSCE; Guiqing Wang, MD, PhD; Robert G. Lerner, MD; Kirsten L. Saetre, DO; Mazen H. Maria, MD; and John A. Branda, MD


Am J Clin Pathol. 2015;144(1):94-96. 

In This Article

Abstract and Introduction


Objectives: Anemia and thrombocytopenia are expected hematologic abnormalities in patients with acute babesiosis, whereas neutropenia (defined as an absolute neutrophil count of ≤1,800 neutrophils/μL for adults and <1,200 neutrophils/μL for infants) is not usually considered a feature of this infection. We studied the frequency with which neutropenia occurs in congenital and adult cases of babesiosis.

Methods: The frequency of neutropenia in cases of congenital babesiosis was determined based on a literature review and on the findings in an unreported case. The frequency of neutropenia in adult patients was assessed based on a review of the medical records of 51 patients who were diagnosed with babesiosis between 2010 and 2013 at two medical centers in the Northeastern United States.

Results: Four (80%; 95% confidence interval [CI], 36%–98%) of five infants with congenital babesiosis whose neutrophil count was reported were neutropenic. Among 51 adult cases with babesiosis, 11 (22%; 95% CI, 12%–35%) were neutropenic on clinical presentation, and seven others developed neutropenia over the next 1 to 21 days. Thus, a total of 18 (35%; 95% CI, 24%–49%) of the adult patients with babesiosis had neutropenia.

Conclusions: Neutropenia appears to be a common finding in infants with congenital babesiosis and is also observed not infrequently in adults with this infection.


Babesiosis is an emerging zoonosis in parts of North America. The most common cause of human infection is Babesia microti.[1] This malaria-like infection is most often transmitted by the bite of an infected Ixodes scapularis tick. It is also transmitted, however, through transfusion of infected blood products and vertically, resulting in congenital babesiosis.[1] Hematologic abnormalities are common in symptomatic cases and include hemolytic anemia, thrombocytopenia, and lymphopenia.[1] Neutropenia has also been observed[2–4] but is not usually listed among the hematologic findings typically associated with this infection.[1] On the contrary, clinicians may view neutropenia as inconsistent with babesiosis, leading them to search for coinfection with Anaplasma phagocytophilum or for other explanations such as autoimmune disease, hematologic malignancy, or other conditions. In this report, we summarize the frequency with which neutropenia was described in all of the reported congenital cases of babesiosis and add information on the presence of neutropenia in an unpublished case of congenital babesiosis. We also report the frequency of neutropenia in 51 adult patients with Giemsa smear–confirmed babesiosis who were diagnosed between 2010 and 2013 at two medical centers in the Northeastern United States.