Babesiosis
Babesiosis is caused by the intraerythrocytic protozoan Babesia microti, transmitted by the blacklegged deer tick or by blood transfusion, producing a hemolytic febrile illness diagnosed on thin blood smear and treated first-line with atovaquone plus azithromycin.
- Topic reviewThe full article, organized the way the exam asks it.
- ABIM-format MCQsVignettes with an explanation for every wrong answer.
- Key factsThe numbers and thresholds worth memorizing, up front.
- AI tutorMedBrain answers the question you're stuck on.
What this article covers
- Overview
Intraerythrocytic protozoal infection: babesiosis is caused by Babesia microti, an intraerythrocytic protozoan spread by the blacklegged (Ixodes) deer tick, the same vector that transmits Lyme…
- Epidemiology
Endemic to areas with the blacklegged tick, overlapping geographically with Lyme disease, and reported with particular frequency around Nantucket, Martha's Vineyard, and Cape Cod, Massachusetts, and…
- Risk factors
Age older than 50 years is the leading risk factor for severe disease.
- Pathophysiology
Tick or transfusion inoculation introduces Babesia sporozoites/merozoites into the bloodstream.
- Clinical features
Fever is the most common symptom (89%), typically accompanied by fatigue (82%), headache (91%), chills, myalgia (44%), and cough (25%); symptoms are nonspecific and mimic many other febrile illnesses.
- Differential diagnosis
Malaria: shares intraerythrocytic ring forms on smear and febrile hemolytic illness; distinguished by travel history to a malaria-endemic region (versus tick exposure in a Lyme-endemic area) and by…
- Diagnosis
Direct visualization of the organism on a thin peripheral blood smear is diagnostic and is the confirmatory basis for the diagnosis: B.
- Management
First, start atovaquone plus azithromycin for mild-to-moderate disease: atovaquone 750 mg PO every 12 hr plus azithromycin 500-1000 mg PO on day 1 then continued daily, for a total of 7-10 days.
- Complications
Splenic rupture, a rare but life-threatening complication of splenomegaly from ongoing hemolysis and splenic filtration.
- Prognosis
Most infections are asymptomatic or mild (approximately 20% asymptomatic), with good outcomes when recognized and treated promptly.
- Prevention
Tick bite avoidance in endemic areas (northeastern/upper midwestern United States) during peak activity season: use EPA-registered tick repellents, wear long clothing, and perform prompt tick checks…
Read the whole article
Subscribing to Internal Medicine opens every article, the full question bank and MedBrain, on the web, iPhone and Android.
Related articles
- Lyme disease
Lyme disease is a tick-borne spirochetal infection caused by Borrelia burgdorferi that progresses from erythema migrans through early disseminated cardiac and neurologic disease to late arthritis, diagnosed clinically when erythema migrans is present and otherwise by two-tiered serology, and treated with staged doxycycline, amoxicillin, or cefuroxime regimens.
- Ehrlichiosis (human monocytic ehrlichiosis)
Ehrlichiosis is a tick-borne febrile illness caused by the obligate intracellular bacterium Ehrlichia chaffeensis, transmitted by the Lone Star tick and infecting monocytes. It is treated empirically with doxycycline without awaiting confirmatory PCR or serology, since delayed treatment raises mortality.
- Malaria
Malaria is a Plasmodium infection acquired from Anopheles mosquito bites, most often diagnosed in returning travelers from sub-Saharan Africa, and severe Plasmodium falciparum disease is a medical emergency treated with IV artesunate.
- Rocky Mountain spotted fever
Rocky Mountain spotted fever is the most common and most severe spotted fever rickettsiosis in the United States, caused by Rickettsia rickettsii and transmitted by the dog tick. The hallmark petechial rash typically lags days behind fever onset, so empiric doxycycline must be started on clinical suspicion alone, since treatment delay drives the disease's disproportionate mortality.