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Atovaquone, a hydroxynaphthoquinone most frequently used in the treatment of Toxoplasma encephalitis in AIDS patients, is a promising agent for the treatment of babesiosis. In in vitro and in vivo studies of B. divergens, atovaquone was more effective than imidocarb, which is routinely used for the treatment of bovine babesiosis and occasionally used for the treatment of European babesiosis (Pudney and Gray,
1997). In this study, severe infection of gerbils was adequately treated with as little as 1 mg/kg body weight of atovaquone. Atovaquone (750 mg every 12 hours) and azithromycin (500 mg on day one, then 250 mg daily thereafter) together may be as effective and less toxic (Krause et al., 1997).
Novel approaches to the treatment of European babesiosis currently under study include the
use of the 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, lovastatin and simvastatin, which inhibit the intraerythrocytic development of B. divergens (Grellier et al.,
1994) and the use of the lipophilic folate analogues, piritrexam and trimetrexate, which inhibited the growth of B. bovis in vitro (Nott and Bagnara, 1993).
Most patients infected with B. microti develop mild or subclinical illness and recover without specific therapy. In severely ill patients, clindamycin (300-600 mg intravenously every 6 hours) and oral quinine (25mg/kg/day in children, 650 mg every 6-8 hours) for 7-10 days appear effective (Wittner et al., 1982; Centers for Disease Control, 1983). Failure of this regimen has occurred (Smith et al., 1986). Other promising agents include atovaquone or azithromycin, either alone or in combination, including with quinine, which were successful in treating B. microti infection in hamsters (Weiss et al., 1993; Hughes and Oz, 1995; Krause et al., 1997).
Chloroquine is ineffective in the treatment of
B. microti infection (Miller et al., 1978). Pentamidine therapy of three patients with intact spleens resulted in clinical improvement but was not curative (Francioli et al., 1981). Other agents that have been of no or questionable value in the treatment of human B. microti infection include quinacrine, primaquine, pyrimethamine, pyri-methamine-sulfadoxine, sulfadiazine and tetracycline. Diminazene aceturate was effective in one patient, who later developed the Guillain-Barre syndrome (Centers for Disease Control,
Erythrocyte exchange transfusions are useful in severely ill patients with high levels of parasitemia and hemolysis (Jacoby et al., 1980; Cahill et al., 1981; Machtinger et al., 1993). When used in conjunction with chemotherapy, the level of parasitemia is reduced. In addition, toxic factors produced by the parasites or of host origin might be removed.
Persons infected with B. microti should receive therapy for early infection with Borrelia burgdorferi because of the well-documented cotransmission of these two pathogens by I. scapularis (Benach et al., 1985; Krause et al., 1996c). Effective regimens include doxycycline, 100 mg b.i.d.; amoxicillin, 500mgq.i.d. (50 mg/ kg/day in children); or cefuroxime axetil, 500 mg
PRINCIPLES AND PRACTICE OF CLINICAL PARASITOLOGY
b.i.d. Unless there is evidence of disseminated Lyme disease, a 10 day course should be sufficient (Steere, 1995).
PREVENTION AND CONTROL
Prevention of human babesiosis relies upon avoidance of exposure to the tick vectors. For I. scapularis, the months of May-September represent the times of greatest activity. In endemic areas, avoidance of grassy areas and brush is advisable. Splenectomized individuals and those who are immunocompromised in other ways should avoid areas of endemicity during times of high tick activity. Clothing should cover the body, especially the lower portion, through wearing long-sleeved shirts and long pants with socks. Tucking pant legs into socks is effective in preventing ticks from crawling up the legs. Ticks are more obvious if light-colored clothing is worn. Insect repellents such as diethyltoluamide (DEET) applied to the skin or clothing, or permethrin applied to clothing only, might be effective. Children and pets should be carefully inspected for ticks. If a tick is found, it should be removed expediently. The tick is grasped below the mouth at the site of attachment to the skin with forceps or tweezers and pulled off steadily. Vaccines against human babesiosis are not available.
Although transfusion-associated babesiosis is rare, this form of transmission can potentially be reduced by discouraging blood donors from endemic areas during times of the year characterized by increased tick activity. Donors with fever within 2 months prior to donation should be avoided. One promising approach to preventing transfusion-associated babesiosis is photosensitization, using lipophilic pheophorbide and red light illumination. This strategy eliminated B. divergens-infected erythrocytes from whole blood (Grellier et al., 1997). Screening of blood for babesiosis is unlikely to be adopted, so the possibility of transfusion-associated babesiosis will remain.