History
The spectrum of babesiosis manifestations is broad, ranging from a silent infection to a fulminant malaria-like disease with fever and chills that results in severe hemolysis and, occasionally, death. Symptoms are thought to be related to the degree of red blood cell (RBC) parasitemia, though this is not always the case.
In the United States, infection with B. microti in otherwise healthy individuals often remains subclinical; however, symptomatic infection is common in asplenic, elderly, and immunocompromised patients. In Europe, because bovine babesiosis due to B. divergens and B. bovis mostly occurs in patients who are asplenic, infections are generally clinically overt and frequently fatal.
Patients typically report a history of travel to an endemic area between May and September. This is the period during which the Ixodes tick is in its infectious nymph stage. Because the nymph, the primary vector, is only 2 mm in diameter when engorged, most patients do not recall a tick bite. The incubation period after the tick bite is usually 1-3 weeks but may occasionally be as long as 9 weeks.
Initial symptoms begin gradually and are nonspecific. Common symptoms include the following:
· Malaise
· Fatigue
· Anorexia
· Shaking chills
· Fever – This may be sustained or intermittent, and temperatures may be as high as 40°C.
· Diaphoresis
· Headache
· Myalgias
· Arthralgias
· Nausea
· Vomiting
· Abdominal pain
· Depression and emotional lability
· Dark urine
· Neck stiffness
· Altered sensorium
· Shortness of breath
· Less commonly, photophobia, conjunctival injection, sore throat, or cough
In a series of 139 patients who were hospitalized with babesiosis in New York, the following were the most common symptoms [24] :
· Fatigue, malaise, and weakness (91%)
· Fever (91%)
· Shaking chills (77%)
· Diaphoresis (69%)
In some untreated patients, symptoms of babesiosis may last for months. Subclinical infections may spontaneously recrudesce after splenectomy and after immunosuppressive therapy.
Physical Examination
Physical exam findings vary with the severity of disease. Most patients have few, if any, physical findings. Fever is generally present. A minority of patients have jaundice, splenomegaly, or hepatomegaly. Petechiae may be present in a few patients, and ecchymoses have been noted occasionally. A rash similar to erythema chronicum migrans has been described, but this probably represents intercurrent Lyme disease. Rigors and altered mental status may be seen. Babesiosis has also been associated with shock and ARDS.
Complications
The complications of babesiosis are often related to the degree of intravascular hemolysis. The main complications include jaundice, hemoglobinuria, and potential renal failure. The following may be observed:
· Shock
· Spontaneous splenic rupture [26, 27]
· Relapse
· Death
Cardiac complications of babesiosis include the following:
· Myocardial infarction
· Congestive heart failure
Renal complications of babesiosis include the following:
· Renal insufficiency
· Renal failure
In severe cases, damage to RBC membranes, decreased deformability, and cytoadherence to capillaries and venules lead to pulmonary edema and respiratory failure. These respiratory problems can begin after treatment has been initiated; researchers have postulated that this is due to intraerythrocytic death of parasites prompting sensitivity to endotoxin. ARDS may occur through mechanisms such as endotoxemia, complement activation, immune complex deposition, cytoadherence, microemboli, and disseminated intravascular coagulation. [11, 28]
Patients who have undergone splenectomy are unable to clear infected RBCs; this inability results in higher levels of parasitemia, eventually leading to hypoxemia and subsequent increased risk of cardiopulmonary arrest. Postsplenectomy patients may also experience hemophagocytic syndrome, acute renal failure, and generalized seizures. Coma can occur, possibly as a consequence of severe sepsis, ARDS, or multiple organ dysfunction syndrome (MODS). [28]
Coinfection with Lyme disease is another possible complication. [29] More research is needed into whether coinfection with Borrelia burgdorferi causes worse morbidity or mortality than either infection alone.
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Peripheral smear showing babesiosis.
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Ixodes scapularis, tick vector for babesiosis. Image courtesy of Centers for Disease Control and Prevention.
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Blood smear showing Babesia species in erythrocytes. Image courtesy of Centers for Disease Control and Prevention.
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Babesia species, tetrad formation. Image courtesy of Centers for Disease Control and Prevention.
