Source:
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.
Frequency:
- 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.
Mortality/Morbidity:
- 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.
Age:
- 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.
History:
- 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.
Physical:
Causes:
- 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.
Treatment:
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.
Medication:
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.
- If the patient does not respond to treatment with clindamycin and quinine,
it may be necessary to switch to azithromycin or
trimethoprim-sulfamethoxazole.
Deterrence/Prevention:
- 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.
Complications:
- 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.
- Coma may be due to severe sepsis, ARDS and multisystem organ failure.
- Co-infection with Lyme disease
Prognosis:
- 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:
- Do not give quinine to a pregnant patient.
- In severe infections, some studies indicate that clindamycin alone may
be just as effective as the combined regimen.