Human Babesiosis in Japan: Isolation of Babesia microti -Like Parasites from an Asymptomatic Transfusion Donor and from a Rodent from an Area Where Babesiosis Is Endemic

Abstract

To determine the source of infection for the Japanese index case of human babesiosis, we analyzed blood samples from an asymptomatic individual whose blood had been transfused into the patient. In addition, we surveyed rodents collected from near the donor's residence. Examination by microscopy and PCR failed to detect the parasite in the donor's blood obtained 8 months after the donation of the blood that was transfused. However, we were able to isolate Babesia parasites by inoculating the blood sample into SCID mice whose circulating red blood cells (RBCs) had been replaced with human RBCs. A Babesia parasite capable of propagating in human RBCs was also isolated from a field mouse (Apodemus speciosus) captured near the donor's residential area. Follow-up surveys over a 1-year period revealed that the donor continued to be asymptomatic but had consistently high immunoglobulin G (IgG) titers in serum and low levels of parasitemia which were microscopically undetectable yet which were repeatedly demonstrable by inoculation into animals. The index case patient's sera contained high titers of IgM and, subsequently, rising titers of IgG antibodies, both of which gradually diminished with the disappearance of the parasitemia. Analysis of the parasite's rRNA gene (rDNA) sequence and immunodominant antigens revealed the similarity between donor and patient isolates. The rodent isolate also had an rDNA sequence that was identical to that of the human isolates but that differed slightly from that of the human isolates by Western blot analysis. We conclude that the index case patient acquired infection by transfusion from a donor who became infected in Japan, that parasitemia in an asymptomatic carrier can persist for more than a year, and that A. speciosus serves as a reservoir of an agent of human babesiosis in Japan.

Epizootiologic Survey for <i>Babesia microti</i> among Small Wild Mammals in Northeastern Eurasia and a Geographic Deversity in the &beta;-Tubulin Gene Sequences

“…Detection of B. microti-specific DNA in blood samples: Nested PCR for detection of Babesia parasites in the blood specimens of the field collections was carried out according to the previously published protocol [31,34]. All oligonucleotide primers used for various PCR are listed in Table 2.…”

“…Our previous investigations on the first Japanese case of human babesiosis [25,34] proved that the patient was infected by blood transfusion from an asymptomatic carrier. A following epidemiological survey [31] further revealed that two types of B. microti-like parasites, namely Kobe and Hobetsu, are enzootic among Japanese small wild rodents, and that Apodemus speciosus, a species of Muridae unique to Japan, serves as the major reservoir of the agent of human babesiosis.…”

Retrospective Seroepidemiological Survey for Human Babesiosis in an Area in Japan Where a Tick-Borne Disease is Endemic.

“…Seemingly identical B. microti-like parasites (designated as the Kobe type) were isolated from both the patient and an asymptomatic carrier who had donated the units of blood that were transfused into the patient. The same type of parasite has also been found in Apodemus mice captured near the donor's residential area [22,23]. More recently, however, we have isolated a number of B. microti-like parasites from wild rodents captured at various places in Japan, and found that another type of parasite (designated as the Hobetsu type), which differs antigenically and genotypically from the Kobe type, is the major type distributed among Japanese small wild rodents [22].…”

“…Strain Ko524 [19] was isolated from the Japanese index case patient in Kobe City, Hyogo Prefecture, Japan [13]. Strain Ho234 was isolated from a large Japanese field mouse (Apodemus speciosus) captured in Hokkaido [23]. These two Japanese strains were serologically distinct, and were used as the type strains of Kobe-and Hobetsu-type parasites, respectively.…”

“…Western blot analysis: The procedure of Western blot analysis has been described previously [1,23]. Babesiainfected erythrocytes were lysed at 4°C in a solution consisting of 10 mM Tris-HCl and 10 mM EDTA (pH 7.5), followed by centrifugation at 10,000 × g for 10 min.…”