Henderson & Groth - e-Medicine

Background: Human Babesiosis is an intra-erythrocytic parasitic infection caused by protozoa of the genus Babesia and transmitted through the bite of the Ixodes tick. The disease most severely affects the elderly, immunocompromised and splenectomized but is usually an asymptomatic infection in healthy individuals.

Pathophysiology: The parasite only infects red blood cells. This leads to a significant effect on the hematological system, including hemolytic anemia, thrombocytopenia and atypical lymphocyte formation. Due to alterations in the red cell membrane, deformability decreases, cytoadherence increases and respiratory distress, in the form of the acute respiratory distress syndrome (ARDS), may develop in those most severely effected.


  • In the US: Babesiosis is a disease that is limited to those who live in or have recently traveled to the Northeastern United States. Few cases have been reported in California, Washington, Wisconsin and Georgia. Hundreds of cases have been reported since the first domestic case of human Babesiosis was reported in 1966. An increasing trend over the past thirty years is thought to be due to restocking the deer population, curtailment of hunting and an increase in outdoor recreational activities. Although the most life-threatening cases occur in the elderly, immunocompromised, and splenectomized, most cases are asymptomatic, which may result in under-reporting of the disease across all age groups.
  • Internationally: Babesiosis in Europe, caused by a different species of Babesia, is a more devastating disease. Although rare, it is symptomatic and often fatal. Like its U.S. counterpart, Babesiosis in Europe is also seen in splenectomized patients.


  • Splenectomized patients are unable to clear the infected RBCs to reduce the level of parasitemia, leading to hypoxemia and subsequent risk of cardiopulmonary arrest. In severe cases, damage to RBC membrane, decreased deformability and cytoadherence to capillaries and venules leads to pulmonary edema and respiratory failure. These respiratory problems begin after treatment has been initiated when intra-erythrocytic death of parasites has been postulated to cause sensitivity to endotoxin. Cases of hemophagocytic syndrome, generalized seizure and acute renal failure have also been reported in asplenic patients.
  • In the U.S., mortality is low. Most cases are asymptomatic and improve spontaneously without treatment. Approximately 25% of Babesiosis patients are co-infected with Lyme disease. These patients experience more severe symptoms for a longer duration than either disease alone.
  • In Europe, Babesiosis is a life-threatening disease. In this region, 84% of patients are asplenic and 53% become comatose and die. Of those rare reported cases of subclinical infection, all were determined to be infected by the same Babesia species that afflicts patients in the northeastern U.S.

Sex: The male:female ratio is about 1:1.



  • Babesiosis affects all age groups with similar frequency; however, patients over age 50 are at increased risk for severe infection and death.
  • Adequate reporting is a major problem, especially in children, due to masking by other infections and the disease's history of occurrence in elderly patients.


  • All patients report a history of travel to an endemic area between the months of May and September. This is the period during which the Ixodes tick is in its infectious nymph stage; however, most do not recall being bitten by a tick.
  • Symptoms include:



  • The causative agent of Babesiosis varies according to the geographical region.
    • In the northeastern U.S., infections are caused by B. microti, transmitted by the same Ixodes tick that transmits Lyme disease.
    • In California and Washington, WA-1, which is similar to B. gibsoni, is the causative agent. The arthropod vector is yet to be identified.
    • In Europe, the Ixodes tick transmits the infectious agent, B. divergens.
  • Occasionally, cases of infection via blood transfusion from a donor who lived in or traveled to an endemic area are reported.


Emergency Department Care: Suspicion of Babesiosis in a patient with a history of tick bite, fever, chills and fatigue is crucial. Peripheral blood smear is needed to make the diagnosis and a CBC with differential is important to determine the severity of infection. Elderly, immunocompromised and splenectomized patients need to be started on a treatment regimen of IV clindamycin and PO quinine immediately to avoid acute renal failure. If the patient is otherwise healthy, supportive care is the only treatment required.

Consultations: Consult infectious disease and medicine if admission is indicated.


Antibiotic and antimalarial therapy should begin immediately after diagnosis to reduce the level of parasitemia. Treatment with clindamycin and quinine is considered most effective as determined through case studies of patient response to different drugs. Patients who do not respond to these drugs may be treated with azithromycin or trimethoprim-sulfamethoxazole.

Further Inpatient Care:

  • Monitor level of oxygenation and watch for the development of respiratory complications that present with dyspnea after the initiation of treatment.
    • The chronology of respiratory distress is thought to be due to sensitivity to endotoxin caused by the medication-induced intra-erythrocytic death of the parasites.
    • In severe cases, exchange transfusion may be the only means of reducing the level of parasitemia. Mechanical ventilation may be necessary should the patient continue to deteriorate.
  • Monitor CBC for development of hemophagocytic syndrome. Examine labs for pancytopenia and patient for lymphadenopathy.

  • If the patient does not respond to treatment with clindamycin and quinine, it may be necessary to switch to azithromycin or trimethoprim-sulfamethoxazole.


  • Those at risk of severe infection should avoid endemic areas between the months of May and September, cover skin with appropriate clothing including long pants tucked inside socks, examine skin and pets every day (takes 24 hours for infection to be transmitted) and wear tick repellent such as diethyltoluamide and dimethyl phthalate on skin and clothes.
  • People from endemic areas who report a fever within the last two months or a history of tick bite are not allowed to donate blood.


  • Noncardiogenic pulmonary edema
  • ARDS is believed to be due to mechanisms such as endotoxemia, complement activation, immune complex deposition, cytoadherence, microemboli, and disseminated intravascular coagulation.
  • Relapses
  • Hemophagocytic syndrome
  • Coma may be due to severe sepsis, ARDS and multisystem organ failure.
  • Co-infection with Lyme disease



  • In the U.S., the prognosis is excellent, and most patients recover spontaneously. Splenectomized patients, however, are at the greatest risk for severe complications and death.
  • In Europe, most symptomatic patients are asplenic, which contributes to a poorer prognosis. Over one-half become comatose and die.

Medical/Legal Pitfalls:

  • Failure to consider diagnosis in children
  • Failure to initiate immediate therapy in high-risk individuals

Special Concerns:

  • Pregnant patients
    • Do not give quinine to a pregnant patient.
    • If the infection is subclinical, no drug therapy is needed.
    • In severe infections, some studies indicate that clindamycin alone may be just as effective as the combined regimen.
  • Geriatric:

    Initiate therapy with clindamycin and quinine immediately.

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