Antigenic and genetic diversities of Babesia ovata in persistently infected cattle

Babesia ovata: Taxonomy, phylogeny and epidemiology

Babesia ovata, which is transmitted by Haemaphysalis longicornis, is an intraerythrocytic protozoan parasite of cattle. Based on its morphology, B. ovata is classified as a large-type Babesia. The developmental stages of B. ovata have been described both in cattle and the tick vector. In infected adult female ticks, the parasite is transovarially transmitted to the tick eggs. The sexual reproduction of B. ovata has been demonstrated in the tick midgut. The diagnostic tools that are currently available for the specific detection of B. ovata in cattle include microscopy and polymerase chain reaction assays. The development of improved molecular and serological diagnostic tools has been constrained by the limited availability of genetic data. B. ovata has been reported in cattle populations in Japan, Korea, China, Mongolia and Thailand. B. ovata was thought to be a benign parasite; however, infections in immuno compromised or Theileria orientalis-infected animals are clinically significant. Thus, control strategies aimed at minimizing the prevalence of B. ovata are vital. The taxonomy of B. ovata is unclear, and the phylogenetic position has not been well defined. Consequently, non-B. ovata species have sometimes been classified as B. ovata. In this review, we provide an outline of the lifecycle, geographical distribution, and control of B. ovata, and critically discuss the taxonomy and phylogeny of this bovine Babesia.

The rediscovery of malaria parasites of ungulates

Over a hundred years since their first description in 1913, the sparsely described malaria parasites (genus Plasmodium) of ungulates have been rediscovered using molecular typing techniques. In the span of weeks, three studies have appeared describing the genetic characterization and phylogenetic analyses of malaria parasites from African antelope (Cephalophus spp.) and goat (Capra aegagrus hircus), Asian water buffalo (Bubalus bubalis), and North American white-tailed deer (Odocoileus virginianus). Here we unify the contributions from those studies with the literature on pre-molecular characterizations of ungulate malaria parasites, which are largely based on surveys of Giemsa-reagent stained blood smears. We present a phylogenetic tree generated from all available ungulate malaria parasite sequence data, and show that parasites from African duiker antelope and goat, Asian water buffalo and New World white-tailed deer group together in a clade, which branches early in Plasmodium evolution. Anopheline mosquitoes appear to be the dominant, if not sole vectors for parasite transmission. We pose questions for future phylogenetic studies, and discuss topics that we hope will spur further molecular and cellular studies of ungulate malaria parasites.

Improvement of the cryopreservation method for the Babesia gibsoni parasite by using commercial freezing media

In vitro cultivation and cryopreservation under liquid nitrogen have already been reported and established for Babesia bovis and Babesia bigemina parasites. Although the in vitro cultivation methods for Babesia gibsoni have been reported and established, the cryopreservation methods for this parasite have not been established completely. In this paper, we compared several freezing media for the cryopreservation of B. gibsoni parasite. The CELLBANKER® series (1 plus and 2), STEM-CELLBANKER®, and CultureSure® were used for commercial freezing media; 10% dimethyl sulfoxide in 90% fetal bovine serum, 20% polyvinylpyrrolidone in phosphate-buffered saline (established for bovine Babesia parasites), and 28% glycerol supplemented with 3% sorbitol and 0.65% NaCl dissolved in water (established for Plasmodium parasites) were used for conventional media. Our results demonstrated that the CELLBANKER® series (1 plus and 2), STEM-CELLBANKER®, and CultureSure® are effective freezing media for B. gibsoni parasite compared to the cryopreservation methods of bovine Babesia and Plasmodium parasites. Our improved method of cryopreservation would contribute to the stability of the in vitro cultivation of B. gibsoni parasite.

A PCR based survey of Babesia ovata in cattle from various Asian, African and South American countries

Babesia ovata is a tick-transmitted hemoprotozoan parasite that infects cattle. In our study, bovine blood samples (n=2,034) were collected from 10 different countries (Brazil, China, Ghana, Japan, Mongolia, the Philippines, South Africa, Sri Lanka, Thailand and Vietnam) and DNA extracted. The DNA samples were screened using an established and specific polymerase chain reaction (PCR) assay targeting the Apical membrane antigen 1 (AMA-1) gene. Parasite DNA was detected among samples collected from Japan, Mongolia and Thailand. Sequence analyses confirmed that the PCR assay detected only B. ovata AMA-1, and that amplicons from different geographical locations were conserved. Our findings highlight the importance of designing adequate strategies to control B. ovata infection in Japan, Mongolia, and Thailand.

PCR detection of Babesia ovata from cattle reared in Japan and clinical significance of coinfection with Theileria orientalis

We describe here the clinical significance of coinfection with Theileria orientalis and Babesia ovata in cattle. Anemia status in a herd of dairy cattle in Japan was investigated in relation to infection with these parasites. Our findings indicate that while B. ovata infection might not be the primary cause of anemia in the cattle, it may contribute to the clinical development of anemia in animals coinfected with both B. ovata and T. orientalis.

Retrospective seroepidemiological survey for human babesiosis in an area in Japan where a tick-borne disease is endemic

A total of 1,335 archived human sera collected in 1985 from an area in Japan where a tick-borne disease is endemic were examined by indirect immunofluorescence antibody test (IFAT) to estimate seroprevalence against three serologically distinct types of Babesia microti-like parasites; namely, Hobetsu, Kobe, and U.S. types. Eighteen sera (1.3%) were found to be IFAT-positive (titer 1:100-1:6,400), of which 14 and three were ascertained by Western blot analysis to be positive against the Hobetsu and Kobe types, respectively. In addition, four sera showed an IFAT titer of 1:100 against the U.S. type, but they appeared to be false-positive because they were cross-reactive against the Hobetsu and Kobe types, and also because a U.S.-type parasite has not been found in Japan. Our results suggest that human babesiosis in Japan occurred prior to the discovery of the index case in 1999 and that the infections were caused mainly by Hobetsu-type parasites.

Human babesiosis in Japan: epizootiologic survey of rodent reservoir and isolation of new type of Babesia microti-like parasite

We have carried out epizootiologic surveys at various sites in Japan to investigate wild animals that serve as reservoirs for the agents of human babesiosis in the country. Small mammals comprising six species, Apodemus speciosus, Apodemus argenteus, Clethrionomys rufocanus, Eothenomys smithii, Crocidura dsinezumi, and Sorex unguiculatus, were trapped at various places, including Hokkaido, Chiba, Shiga, Hyogo, Shimane, and Tokushima Prefectures. Animals harboring Babesia microti-like parasites were detected in all six prefectures. Inoculation of their blood samples into hamsters gave rise to a total of 20 parasite isolates; 19 were from A. speciosus, and the other 1 was from C. rufocanus. Sequencing of the parasite small-subunit rRNA gene (rDNA) sequence revealed that 2 of the 20 isolates were classified as Kobe type because their rDNAs were identical to that of the Kobe strain (the strain from the Japanese index case). The other 18 isolates were classified as a new type, designated the Hobetsu type, because they all shared an identical rDNA sequence which differed significantly from both that of Kobe-type isolates and that of northeastern United States B. microti (U.S. type). The parasites with Kobe-, Hobetsu- and U.S.-type rDNAs were phylogenetically closely related to each other but clearly different from each other antigenically. The isolates from rodents were demonstrated to be infective for human erythrocytes by inoculation into SCID mice whose erythrocytes had been replaced with human erythrocytes. The results suggest that a new type of B. microti-like parasite, namely, the Hobetsu type, is the major one which is prevalent among Japanese wild rodents, that A. speciosus serves as a major reservoir for both Kobe- and Hobetsu-type B. microti-like parasites, and that C. rufocanus may also be an additional reservoir on Hokkaido Island.

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

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.