A 48-year-old man comes to the hospital due to 10 days of persistent fever, chills, fatigue, and dyspnea. He had a splenectomy at age 28 after a motor vehicle accident and is up to date on appropriate vaccinations. The patient does not use tobacco, alcohol, or illicit drugs. He recently traveled from New York City to Connecticut for a family wedding. His temperature is 38.6 C (101.5 F), blood pressure is 118/70 mm Hg, and pulse is 108/min. Lung examination reveals coarse crackles. Laboratory results are as follows:
| Complete blood count | |
| Hemoglobin | 9.6 g/dL |
| Reticulocytes | 4% |
| Platelets | 108,000/mm3 |
| Leukocytes | 11,000/mm3 |
| Liver function studies | |
| Total bilirubin | 1.8 mg/dL |
| Direct bilirubin | 0.6 mg/dL |
| Alkaline phosphatase | 120 U/L |
| Aspartate aminotransferase (SGOT) | 87 U/L |
| Alanine aminotransferase (SGPT) | 74 U/L |
| Lactate dehydrogenase | 188 U/L (normal: 45-90 U/L) |
| Haptoglobin | 36 mg/dL (normal: 50-150 mg/dL) |
Chest x-ray reveals bilateral infiltrates. A peripheral blood smear shows normocytic, normochromic anemia with ring- and cross-shaped intraerythrocytic inclusions. The vector responsible for this patient's current condition can also transmit which of the following organisms?
Babesiosis | |
Epidemiology |
|
Clinical manifestations |
|
Diagnosis |
|
ARDS = acute respiratory distress syndrome; CHF = congestive heart failure; DIC = disseminated intravascular coagulation; HGA = human granulocytic anaplasmosis; LFTs = liver function tests. | |
This patient with an acute febrile illness, thrombocytopenia, hemolytic anemia (indirect hyperbilirubinemia, elevated lactate dehydrogenase, low haptoglobin), abnormal liver function tests, and intraerythrocytic inclusions (ring-shaped and "Maltese cross" forms) has babesiosis, a tick-borne infection. A definitive diagnosis can be made from a Giemsa-stained blood smear showing intraerythrocytic parasites. Splenectomy places patients at increased risk for severe babesiosis, which can manifest as acute respiratory distress syndrome (dyspnea, coarse crackles, bilateral infiltrates on chest x-ray).
Babesiosis (caused by Babesia microti) and Lyme disease (caused by Borrelia burgdorferi) are both transmitted by the Ixodes tick and occur in similar geographic regions; coinfection is common.
(Choices B and F) Dengue virus is transmitted by Aedes mosquitos, and Plasmodium falciparum is transmitted by Anopheles mosquitos. Dengue fever and malaria may present as acute febrile illnesses, but both infections occur mainly in tropical regions. In addition, blood smears in patients with malaria show only ring-shaped (not cross-shaped) erythrocyte inclusions.
(Choices C and E) Asplenic patients are at increased risk for life-threatening infections with encapsulated organisms (eg, Streptococcus pneumoniae, Haemophilus influenzae, Neisseria meningitidis). However, intraerythrocytic inclusions would not be expected.
(Choice D) Histoplasmosis is a common mycotic infection that is most commonly found in the Ohio and Mississippi river basins and is associated with activities involving exposure to bird or bat droppings (eg, caving).
Educational objective:
Babesiosis and Lyme disease are transmitted by the Ixodes tick and occur in similar geographic regions. Coinfection is common.