Babesia

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Summary of Babesia

Babesia is a genus of protozoa that infect the blood and cause a parasitic, hemolytic disease known as babesiosis. Transmission is via the Ixodes tick, the same species that often carries Borrelia burgdorferi (the cause of Lyme disease), and thus coinfection with these two parasites may occur in a patient. The endemic region is the northeastern United States. People who contract babesiosis suffer from malaria-like symptoms, such as hemolytic anemia and fever. Individuals without a spleen are at increased risk for severe disease. Microscopic analysis may show a ring form or "maltese-cross" within red blood cells. Treatment is with Atovaquone and azithromycin.

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Babesia

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BABESIA osms.it/babesia PATHOLOGY & CAUSES RISK FACTORS ▪ Malaria-like parasitic infection ▫ Ixodes tick transmission ▪ Phylum Apicomplexa (same as Plasmodium, Toxoplasmosis) ▪ Common species ▫ Babesia microti most predominant (northeast, upper midwest United States) ▫ B. duncani (Western United States) ▫ B. divergens (Europe) ▪ Endemic area resident ▪ Endemic area travel, especially May– September ▪ Blood transfusion (last six months) ▪ Age > 50 ▪ Biologically male ▪ Asplenia ▪ Decreased immunity (malignancy, HIV/ AIDS infection, immunosuppressive drugs) ▪ Coinfection with Borrelia and/or Anaplasma ▪ Premature birth CAUSES COMPLICATIONS ▪ Ixodes scapularis tick: only recognized vector ▫ Same tick transmits Borrelia burgdorferi (→ Lyme disease; concurrently infects ⅔ babesiosis-infected individuals) and Anaplasma phagocytophilum (→ human granulocytic anaplasmosis; concurrently infects ⅓ babesiosis-infected individuals) ▫ Contaminated blood transfusion → rare human-to-human transmission ▪ Life cycle ▫ Two hosts: white-footed mouse, Ixodes tick (deﬁnitive) ▫ Blood meal → Babesia-infected tick sporozoites into mouse host → sporozoites directly invade mature mouse erythrocytes → sporogony (asexual reproduction; budding) → in blood, some parasites differentiate into male, female gametes → gametes unite → sporogonic cycle → sporozoites → tick bites human → 1–4 week incubation → sporozoites enter erythrocytes → sporogony ▪ Sporogony ▫ Asynchronous with host → no massive hemolysis (versus malaria) ▪ Tick’s nymph stage is most infectious 412 OSMOSIS.ORG ▪ ↑ occurence in anemic/parasitemic individuals ▫ Congestive heart failure ▫ Noncardiac pulmonary edema ▫ Acute respiratory distress syndrome ▫ Splenic infarct ▫ Splenic rupture ▫ Septic shock ▫ Myocardial infarction ▫ Disseminated intravascular coagulation ▫ Death SIGNS & SYMPTOMS ▪ Mostly asymptomatic, may persist undiagnosed months/years ▪ Blood-stage parasite multiplication → clinical manifestation ▪ Non-speciﬁc ﬂu-like symptoms (misdiagnosis common) ▫ Fatigue (gradual onset) ▫ Fever, chills, sweats ▫ Headache, myalgia, arthralgia ▫ Anorexia, nausea ▫ Cough

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Babesia

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A 42-year-old man is brought to the emergency department because of a high fever which started 2 days ago. He appears acutely ill and reports that he has been feeling tired and short of breath, and has noticed his urine is darker than normal. His temperature is 38.7°C (101.6°F), pulse is 94/min, respirations are 22/min, and blood pressure is 95/60 mm Hg. His past medical history includes idiopathic thrombocytopenic purpura, for which he had a splenectomy. He has recently returned from a 2-week summer holiday to Tanzania. Laboratory studies show:

A peripheral blood smear shows an intraerythrocytic ring form and a ‘Maltese cross’ (tetrad) sign. Which of the following organisms is the most likely cause of this patient’s symptoms?

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