Transmission Studies of Babesia microti in Ixodes ricinus Ticks and Gerbils

Abstract

In order to investigate the possible role of Ixodes ricinus as a vector of zoonotic Babesia microti infection inEurope, a European rodent isolate (HK) and a zoonotic American isolate (GI) were studied in transmission experiments. PCR detected B. microti in the blood and spleens of infected gerbils (Meriones unguiculatus) and also in laboratory-induced infections of I. ricinus ticks. B. microti DNA was detected by PCR in all pooled samples of nymphs and the majority of adults that had fed as larvae and nymphs, respectively, on gerbils with acute infection of the European isolate, confirming that I. ricinus could serve as a vector in Europe. The American isolate, GI, proved to be equally infective for larval and nymphal I. ricinus as the HK strain, despite a very different appearance in gerbil erythrocytes. Nymphs infected with the HK and GI strains readily infected gerbils. In contrast to the finding in acute infections, ticks that fed on gerbils with chronic infections of HK and GI did not become infected. It was also found that the HK strain was not transmitted transovarially. The finding that a B. microti strain (GI) from a distant geographical region (United States) can infect and be transmitted by I. ricinus suggests that other European B. microti strains, in addition to the HK strain used here, are probably infective for I. ricinus, supporting the view that infection of humans with European B. microti may be a regular occurrence.Babesia microti is a tick-transmitted rodent blood parasite that was first reported as a cause of human disease in 1969 in the northeastern United States (23). Several hundred cases are now reported from this region each year (7). The disease is characterized by a gradual onset of malaise with anorexia, fever, headaches, myalgia, and other vague symptoms which may persist for long periods. Occasionally dangerous fulminating infections occur, particularly in immunocompromised or aged individuals. The vector is the tick Ixodes scapularis, and transmission is transstadial, the infection being acquired from mice (e.g., the white-footed mouse, Peromyscus leucopus) by larval or nymphal ticks and transmitted by nymphs or adults (5). Transovarial transmission, which occurs in other Babesia species, such as B. canis and B. bovis, has not been reported in B. microti (19).Babesia microti is also present throughout Europe, but no verified cases of human disease have been reported. This may be because the rodent tick Ixodes trianguliceps, implicated as the main vector in Europe (5, 7), does not bite humans. However, it has been shown that at least one European strain of B. microti may be transmitted by Ixodes ricinus (21), which is known to be a vector of several zoonotic diseases (4), and seroprevalence studies suggest that infection of humans with B. microti may occur in Europe (6, 9). In the present study, the infectivity for I. ricinus of a European strain and a zoonotic American strain of B. microti was investigated by PCR and by transmission to and from gerbils (Meriones unguiculatus). MAT...

Babesia microti-Group Parasites Compared Phylogenetically by Complete Sequencing of the CCT.ETA. Gene in 36 Isolates

“…The U.S. type included parasites of the Gray, GI, NM69, and AK2273 strains and the Vladivostok38, Korea8, and Xinjiang1637 isolates [30,43,44] in addition to the HK strain [10] and an isolate obtained from Clethrionomys rutilus captured in Russia (Irkutsk16). The HK and Irkutsk16 isolates were provided by Jeremy Gray (University College Dublin, Ireland) and Hiroaki Kariwa (Hokkaido University, Japan), respectively, and assigned tentatively to the U.S.…”

Molecular examinations of Babesia microti in rodents and rodent-attached ticks from urban and sylvatic habitats in Germany

“…While transovarial transmission in ticks was confirmed for B. divergens and other Babesia species, experimentations have failed to demonstrate transovarial transmission for B. microti [Gray et al 2010]. Therefore mammalian hosts are essential for its maintenance in natural transmission cycles [Gray et al 2002].…”

“…Microtine voles have been discussed as reservoir hosts for the intraerythrocytic protozoan Babesia microti (phylum Apicomplexa, order Piroplasmida) [Gray et al 2002]. It was first described in a vole near Lisbon in 1910 as Smithia microtia (Microtus incertus, now Microtus arvalis subspecies incertus, the common vole [Walter 1981].…”

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

“…Although experimental transmission of B. microti U.S. lineage to hamsters or gerbils has been shown (33,36), there is still a lack of biological evidence demonstrating the live pathogen in field-derived specimens. In this study, we provide direct evidence that I. persulcatus ticks carry the infectious B. microti U.S. lineage in their salivary glands.…”