HUMAN BABESIOSIS
Symptoms
Babesia microti infection in humans frequently remains asymptomatic. Severe and fatal cases of human babesiosis usually diagnosed in patients possessed a weakened immune system, especially those without an intact spleen. Clinical signs of the disease vary from one individual to another and symptoms are typically present within 1 to 4 weeks following a tick bite. A gradual onset of malaise, anorexia, and fatigue are commonly observed in the early stages of the disease and within a week or so, fever, drenching sweats, and myalgia can develop. A skin rash (erythema migrans), the telltale sign of Lyme disease, is not associated with human babesiosis. Patients typically have fever that range from 37.8 to 40.3 C and commonly show signs of nausea, vomiting, headache, shaking chills, hemoglobinuria, hyperresthesia, and emotional lability and depression. Pulmonary edema is occasionally presented by the patients. In addition, splenomegaly may occur, but it is rather atypical. Parasitemias which develop are usually at low levels. In spleen-intact patients, parasitemias may range from 1 to 20%, however, a parasitemic level of 85% in severe human babesiosis has been reported. Hemolytic anemia and thrombocytopenia have been frequently found, and dark urine also may be observed. Patient leukocyte counts are typically in the low to normal ranges. In some patients, elevated levels of dehydrogenase, bilirubin, and transaminase may be encountered.
Diagnosis
Babesia microti is an intracellular parasite within the erythrocytes, therefore, diagnosis of human babesiosis has relied heavily upon the determination of the presence of the erythrocytic stage of the organism. Examination of Giemsa-stained thin blood smears is considered the most useful diagnostic procedure. The tetrad forms (Maltese-cross) of the parasite are believed to be the primary diagnostic character for the disease. However, the predominant forms in most of the blood smears closely resemble rings of Plasmodium spp., with small to large cytoplasmic vacuoles. Therefore, it is difficult to differentiate Babesia microti from Plasmodium spp., especially Plasmodium falciparum. It is recommended that diagnosis of clinical case of human babesiosis be made by a combination of criteria including the presence of intense parasitemias (1-50%), erythrocytes infected by multiple basket-shaped parasites, and the presence of extracellular merozoites. In addition, Babesia microti infection in humans appears to trigger humoral immune responses. An indirect immunofluorescent antibody assay (IFA) procedure has been widely used in the diagnosis of clinical cases and in prevalence determination of the infection in human populations. Although high titers (even at 1:4096) have been detected in patients during the acute phase, a cut-off point of 1:64 is generally accepted as diagnostic in IFA testing Cross-reaction does occur in anti-sera to Babesia microti with other Babesia species including Babesia argentina, Babesia bigemina, and Babesia caballi, particularly at lower dilutions and during the acute phase of the disease. However, it does not cross react with other arthropod-borne pathogens such as those causing malaria and Colorado tick fever. Subinoculation of blood samples from patients into hamsters may provide assistance in diagnosis by amplifying the parasitemia. In addition, use of Polymerase Chain Reaction (PCR )has proven to facilitate the diagnosis of zoonotic babesial infections. By using genus- and species-specific primers, a definitive diagnosis can be made within a day and may further improve the sensitivity of the hamster inoculation method.
Treatment
Most patients infected with Babesia microti appear to experience only mild clincal manifestations; therefore, they normally require no specific treatment. For those who do need treatment, the drugs administered have not been reliable but in some instances toxicity of the therapeutic procedures seems to be problematic. Chloroquine was first recommended and used as the chemotherapeutic choice for the treatment. Although, the therapy improves symptoms of some patients with Babesia microti infection, the parasitemias appear to be maintained. Similar studies in hamsters also revealed that treatments with chloroquine, metronidazole, primaquine, and sulfadiazine in combination with pyrimethamine have no effects on the elimination of the parasitemia. In addition, the effectiveness of quinine and pyrimethamine in babesiosis treatment has been inconclusive. The use of cotrimoxazole is generally an ineffective treatment method for human babesiosis. Both pentamidine and berenil therapies can effectively control the parasitemia, but fail to eliminate the parasites completely. Furthermore, administrating 50 mg/kg of pentamidine resulted in 100% mortality in animals. Currently, administration of quinine combined with clindamycin is the treatment of choice for human babesiosis. The parasitemia is consistently eradicated after the administration of the drugs and that there is no recurrance of the babesial infection after the discontinuation of the treatment.
HUMAN BABESIOSIS
TICK VECTORS AND RESERVOIR
HOSTS
EPIDEMIOLOGY
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