Chapter 342. Babesiosis

Babesiosis is a malaria-like illness caused by intraerythrocytic protozoa that are transmitted by the bite of the same hard-bodied ticks (Ixodid) that transmit Lyme disease and human granulocytic anaplasmosis.1-2 Babesia species are parasites of mammals and birds that are currently classified in the subphylum Apicomplexa, together with those organisms that cause malaria (Plasmodium sp.) and toxoplasmosis (Toxoplasma gondii). Only a few of the more than 90 species of Babesia cause disease in humans including, Babesia microti and Babesia microti-like species from the United States, Asia, and Europe, Babesia duncani (WA1) from California and Washington State, Babesia divergens and Babesia divergens-like species from Europe and the United States, and Babesia venatorum (EU1) from Europe.2-3

Although babesiosis has long been recognized as an economically important disease in livestock, the first human case was not described until 1957. Over the past 30 years, the epidemiology of the disease has changed from a few isolated cases to the establishment of endemic areas in southern New England, New York, and the upper Midwest, and reports come from a wide geographic range in America, Africa, Asia, and Europe.1-2 The incidence of babesial infection is similar in children and adults (eFig. 342.1).4 Human babesiosis is transmitted in the northeastern United States by deer ticks (Ixodes scapularis) that feed from infected animal reservoirs (primarily the white-footed mouse, Peromyscus leucopus).5 Nymphal ticks feed in the late spring and summer, and those that are infected transmit B. microti to rodents or man. Consequently, most human cases of babesiosis occur in the summer. The white-tailed deer is an important host of the deer tick. The recent increase in the deer population is thought to be a major cause of the increased incidence of human babesiosis, human granulocytic anaplasmosis, and Lyme borreliosis. Rarely, babesiosis is acquired through blood transfusion or transplacental-perinatal transmission.6-8

Clinical Manifestations

The clinical manifestations of babesiosis range from subclinical illness to fulminating disease resulting in death or prolonged convalescence.1-3 Symptoms begin after an incubation period of 1 to 6 weeks from the beginning of tick feeding. The unengorged I. scapularis deer tick is only about 2 mm in length, so there is often no recollection of a tick bite. Typical symptoms include intermittent temperature to as high as 40°C (104°F) and one or more of the following: chills, sweats, myalgia, arthralgia, nausea, and vomiting. Other less common clinical manifestations are emotional lability and depression, hyperesthesia, headache, sore throat, abdominal pain, conjunctival injection, photophobia, weight loss, and nonproductive cough.

While the number of symptoms appears to be similar in children and adults, the duration of symptoms and frequency of hospitalization is greater in adults over 50 years of age. Adults and children who are immunocompromised, especially those who lack a spleen or who have HIV or malignancy, are at increased risk of life-threatening disease.9,10The overall babesiosis mortality rate is about 5% but as high as 21% in highly immunocompromised hosts. B. microti may be co-transmitted with the agents causing Lyme disease and human granulocytic anaplasmosis. Patients experiencing babesiosis and Lyme disease coinfection generally have an increase in the number of symptoms and a longer duration of illness compared with patients experiencing Lyme disease alone.11 Asymptomatic babesial infection may persist for months or even years and may result in disease recrudescence or transmission of babesiosis through blood donation.12

Diagnosis

The diagnosis of babesiosis should be considered in any person experiencing fever who has been in an endemic area or who has received a blood transfusion. Specific diagnosis is best made by detecting the organism in red blood cells using Giemsa-stained thin blood smears (Fig. 342-1).1-2 Severe cases include the presence of intense parasitemia (10–50%), but parasitemia may be sparse (< 1%), especially early in the course of illness. Other means of detection include amplifying parasite DNA using polymerase chain reaction (PCR) and serology. PCR is highly sensitive and specific and can be rapidly performed; however, scrupulous technique must be maintained to prevent false-positive results. Serology also may confirm a diagnosis of babesiosis when parasites are scarce or not detectable. A patients’ serum often reacts at high titer during the acute illness. An IFA titer of at least 1:64 generally is considered to be diagnostic. The antibody response appears to wane within a year.

Treatment and Prevention

The combination of atovaquone (40 mg/kg per day divided Q12H PO) and azithromycin (12 mg/kg per day given Q24H PO) or clindamycin (20 to 40 mg/kg per day divided Q8H PO) and quinine (25 mg/kg per day divided Q8H PO) administered for 7 to 10 days should be used to treat babesiosis.2 Atovaquone and azithromycin are as effective as clindamycin and quinine for mild to moderate disease but are associated with a much lower rate of untoward reactions.13 Clindamycin and quinine remains the treatment of choice for severe disease. Treatment failures have been reported for both drug combinations in immunocompromised patients, and prolonged therapy in such cases may be necessary.9 Exchange blood transfusion should be used in the most severe infections, such as those with a high parasitemia (over 5%), coma, hypotension, congestive heart failure, pulmonary edema, or renal failure.2,14 Partial or whole exchange transfusion can rapidly decrease the degree of parasitemia and can remove toxic by-products of babesial infection.

Preventing babesiosis can be accomplished by avoiding ticks and tick-infested areas during the transmission season.15 High-risk groups should be especially careful to avoid areas where deer ticks are found in abundance. When exposure is unavoidable in endemic areas, clothing that covers the lower part of the body should be worn. Tick repellants may be used on skin (DEET [N,N-Diethyl-meta-toluamide]) or on clothing (Permanone or Duranone) as directed by the manufacturer. DEET should be used sparingly because of rare reports of serious neurological complications resulting from excessive application, especially to the face, hands, or abraded skin. Removal of ticks from people and pets should be carried out using tweezers and gently retracting the tick. No data exists to recommend administering prophylactic antibiotics after a tick bite to prevent babesiosis.