The Diagnosis
The patient in this case study was diagnosed with an acute Babesia microti infection. The smear was diagnostic for the piroplasm. The presence of a maltese cross arrangement of the organisms in one of the red cells in the smear is very characteristic of Babesia microti. There were also a number of extracellular parasites present in the smear. Sometimes the smears of heavily infected individuals are described as having a “dirty” appearance because of these extracellular appearing Babesia. These two characteristics seen in the smear initially had me leaning towards Babesiosis.
Other than the characteristic smear this was an unusual and unexpected case of babesiosis. The clinician in the Emergency Room initially was skeptical of our assessment of the smear. The clinician requested an Infectious Disease and Pathologist consult on the case along with a review of the smear. The initial assessment was confirmed by the Infectious Disease Physician and Pathologist.
The unusual part of this case was that the patient was not considered geographically at risk for Babesiosis. The parasite is not known to be endemic in the north central parts of Connecticut. Most cases are from individuals exposed to tick bites on the Connecticut Coast, the Rhode Island Coast and Cape Cod in Massachusetts. The patient did not have a history of travel to any of these endemic areas. However, the patient did have a large exposure to tick bites from gardening in her back yard. Numerous tick bites were noted on her physical exam as well as the removal of three imbedded engorged ticks. Considering her advanced age, and lack of mobility, she was very much at risk for acquiring ticks from her gardening. Additionally, her daughter said she was not compliant at using repellants because she claimed to have a sensitivity to them.
A further review of her medical records revealed that she was asplenic which further placed her at risk for an acute infection due to Babesia microti. Patients who are asplenic are at an increased risk for severe and overwhelming infections with Babesia and encapsulated bacteria such as Streptococcus pneumoniae.
Many times, inexperienced hematologists or microbiologist can mistake Babesia for Plasmodium. Afterall, they are related. However, the Babesia have the tick as a vector while the Plasmodium will have the anopheles mosquito as its vector. In the Northeast United States the Babesia species endemic is Babesia microti and its tick vector is Ixodes scapularis. The White-footed mouse (Peromyscus leucopus) is the main reservoir for Babesia microti in the Northeast. Meadow voles (Microtus pennsylvanicus) can also act as reservoirs for the piroplasm.
The Babesia are zoonotic and very commonly spread across wild mammals. Humans are thought of as accidental hosts. And though we like to simplify the Babesia into two species, microti and divergens, there is much more complexity to be found within the species such as subspecies, strain types as well as other recognized species. We will keep it simple here and stick with the two clinically predominant species causing disease in humans.
B. microti generally produces the milder disease of the two, though asplenism and immunodeficiency will greatly enhance the severity of disease in these individuals. B. microti is generally found in the United States (Northeast, upper Midwest, and mid-Atlantic). The vector as previously mentioned is the Ixodes scapularis tick and the reservoir are rodents with the White-footed mouse playing a large role. Severe infections will require treatment with antibiotics and blood transfusions if needed. Given the right unfortunate circumstances the infection can still prove to be fatal in the most vulnerable.
In Europe the Babesia species endemic is B. divergens. The vector for the piroplasm is the Ixodes ricinus tick with bovines acting as the reservoir. B. divergens is much more pathogenic than it’s across the ocean cousin B. microti. The disease is acute even in those that are not asplenic and are immunocompetent. A diagnosis of B. divergens infection requires prompt treatment because of the severity of infection. Failure to initiate treatment in a timely fashion with B. divergens infections will lead to major organ failure and death. Prompt therapy, blood transfusions, and ventilation if required, will reduce the chance of death in these patients.
The patient in the presentation was brought to the emergency room weak and disoriented. The smear was significant for the presence of Babesia microti organisms. Due to the acute infection leading to a high destruction of red blood cells, her complete blood cell count was significant for an abnormally low hemoglobin and hematocrit. The anemia contributed to her weakness and disorientation. Low white and platelet counts are not uncommon in these infections as are abnormal liver enzymes.
The patient was admitted, provided a blood transfusion, and started on a 10-day treatment with clindamycin plus quinine. She had an uneventful recovery and was discharged with no residual comorbidity noted. The daughter was instructed to make sure that her gardening be limited. Protective clothing and the use of tick repellant was emphasized.