Ixodes persulcatus Ticks as Vectors for the Babesia microti U.S. Lineage in Japan

Abstract

The U.S. lineage, one of the major clades in the Babesia microti group, is known as a causal agent of human babesiosis mostly in the northeastern and upper midwestern United States. This lineage, however, also is distributed throughout the temperate zone of Eurasia with several reported human cases, although convincing evidence of the identity of the specific vector(s) in this area is lacking. Here, the goal was to demonstrate the presence of infectious parasites directly in salivary glands of Ixodes persulcatus, from which U.S. lineage genetic sequences have been detected in Asia, and to molecularly characterize the isolates. Five PCRpositive specimens were individually inoculated into hamsters, resulting in infections in four; consequently, four strains were newly established. Molecular characterization, including 18S rRNA, ␤-tubulin, and CCT7 gene sequences, as well as Western blot analysis and indirect fluorescent antibody assay, revealed that all four strains were identical to each other and to the U.S. lineage strains isolated from rodents captured in Japan. The 18S rRNA gene sequence from the isolates was identical to those from I. persulcatus in Russia and China, but the genetic and antigenic profiles of the Japanese parasites differ from those in the United States and Europe. Together with previous epidemiological and transmission studies, we conclude that I. persulcatus is likely the principal vector for the B. microti U.S. lineage in Japan and presumably in northeastern Eurasia. IMPORTANCEThe major cause of human babesiosis, the tick-borne blood parasite Babesia microti, U.S. lineage, is widely distributed in the temperate Northern Hemisphere. However, the specific tick vector(s) remains unidentified in Eurasia, where there are people with antibodies to the B. microti U.S. lineage and cases of human babesiosis. In this study, the first isolation of B. microti U.S. lineage from Ixodes persulcatus ticks, a principal vector for many tick-borne diseases, is described in Japan. Limited antigenic cross-reaction was found between the Japan and United States isolates. Thus, current serological tests based on U.S. isolates may underestimate B. microti occurrence outside the United States. This study and previous studies indicate that I. persulcatus is part of the B. microti U.S. lineage life cycle in Japan and, presumably, northeastern Eurasia. This report will be important for public health, especially since infection may occur through transfusion, and also to researchers in the field of parasitology.

Analysis of antigen‐antibody cross‐reactivity among lineages and sublineages of Babesia microti parasites using human babesiosis specimens

“…However, these samples showed lower reactivity to IpSG‐13‐16‐3, which belongs to the East Asia sublineage of the US lineage. Previous animal experiments indicated low antigen‐antibody cross‐reactivity in hamster sera between the North America and East Asia sublineages of the US lineage . In this study, even in human cases, individuals who might have been infected with the North America sublineage of the US lineage showed lower reactivity to the East Asia sublineage.…”

“…Ho234 (Hobetsu lineage) was isolated from a rodent in Japan . The lineages and sublineages of the US lineage of the B. microti strains used were previously determined by phylogenetic analysis based on the sequences of B. microti 18S rRNA, β‐tubulin, and CCT‐eta genes …”

“…B. microti DNA was extracted from 100 μL of human RBCs using a QIAamp DNA Mini Kit (Qiagen). The extracted DNA was used as the template for amplification of 18S rRNA, β‐tubulin, or CCT‐eta genes of B. microti with nested PCR using the primers shown in Table . The PCR products were subjected to sequencing using a cycle sequencing kit (BigDye Terminator v1.1, Thermo Fisher Scientific).…”

“…The B. microti US lineage has been also detected in Europe, Asia, and South America in specimens from humans, rodents, and ticks. Based on the genetic diversity of the B. microti genes encoding β‐tubulin and the chaperonin‐containing TCP1 subunit eta (CCT‐eta), the B. microti US lineage is phylogenetically classified into three sublineages: North America, Europe‐Central Asia, and East Asia . The name of each of these US sublineages reflects its geographic origin.…”

Molecular Detection and Characterization of Zoonotic and Veterinary Pathogens in Ticks from Northeastern China

“…In China, B. microti has been found in rodents in Fujian, Zhejiang, Henan, and Heilongjiang provinces (Sun et al, 2008; Zhao et al, 2013; Chen et al, 2014); B. divergens has been described in I. persulcatus , Haemaphysalis concinna , and H. japonica and striped field mice in Heilongjiang province, where B. venatorum has also been reported in I. persulcatus (Fang et al, 2015; Jiang et al, 2015). Most ixodid tick species, such as Ixodes scapularis in the United States, Ixodes ricinus in Europe, and I. persulcatus in Asia, can transmit Babesia parasites to their natural hosts (Brasseur and Gorenflot, 1996; Sun et al, 2008; Schulze et al, 2013; Zamoto-Niikura et al, 2016). …”