Mite Vectors (Acari: Trombiculidae) of Scrub Typhus in a New Endemic Area in Northern Kyoto, Japan

Abstract

Between 1983 and 1999, 27 human cases of scrub typhus (two fatal) occurred in the Nodagawa River basin of northern Kyoto, Japan, an area where no cases had been previously reported. Antibody screening of infected patients' sera showed that nine of 15 patients had high titers against the Gilliam type of Orientia tsutsugamushi (Hayashi). To determine the vector mite transmitting the disease, we studied rodent and chigger populations in and near a rice field alongside the Nodagawa River between 1996 and 1999. The most common rodent species was Microtus montebelli (Milne-Edwards), representing 73.3% (33/45) of the population. The mite index (average number of mites per infested host) was highest (190.8) in Leptotrombidium pallidum Nagayo, Mitamura & Tamiya parasitizing on M. montebelli, followed by Leptotrombidium intermedium (Nagayo, Mitamura & Tamiya) (174.9) on the same host species. Orientia tsutsugamushi was isolated from 60.5% (23/38) of rodents and from 71.2% (37/52) of pools of engorged L. pallidum. The Gilliam type of O. tsutsugamushi was most prevalent in rodents, and in engorged L. pallidum and it was the only type recovered from 10 isolates inoculated into L 929 cells for indirect immunofluorescence examination. Orientia tsutsugamushi infected 14.3% (181/1263) and 14.8% (306/2066) of engorged and unfed L. pallidum larvae, respectively, and was also detected in 0.055% (2/3634) of unfed L. intermedium, although previous studies suggest that this mite rarely bites humans. These results show that L. pallidum is the primary vector species of scrub typhus in this new endemic area in Japan.

Rodent-borne diseases and their risks for public health

“…This pathogen is transmitted by bites from infected trombiculid mites ('chiggers') that are hosted by various rodent species, such as the Norway rat (R. norvegicus), the lesser bandicoot (Bandicoota bengalensis), the bandicoot rat (Bandicoota indica), house mouse (Mus musculus), the striped-field mouse (Apodemus agrarius), and the Japanese grass vole Microtus montebelli (Milne-Edwards) (Kumar et al 2004;Liu et al 2003;Takahashi et al 2004). Cases of scrub typhus have been reported from Southern and Eastern-Asia (Japan, Indonesia, Korea, Thailand, Asiatic Russia, the Indian subcontinent, Pakistan, China), and Australia (Graves et al 2006;Khuntirat et al 2003;Kim et al 2007;Liu et al 2003;Sin et al 2000;Takahashi et al 2004;Traub et al 1954;Yahnke et al 2001). In Australia, hosts of chiggers include introduced rodent species, native rodent species and small marsupials, particularly the long-nosed bandicoot, Perameles nasuta, and scrub typhus has been reported down the east coast of Australia (Spratt 2005).…”

Scrub Typhus: The Geographic Distribution of Phenotypic and Genotypic Variants ofOrientia tsutsugamushi

“…Of 4 patient isolates that showed dramatic variability in murine virulence, 1 was typed as Kawasaki and 1 as Kuroki by use of IFA with monoclonal antibodies [83,249]. The most extensive use of molecular methods to characterize strains has been in Japan [54,165,166,176,185,186,190,194,195,[250][251][252]. All methods (PCR primer-specific typing, RFLP, and sequencing) have been used in various studies.…”

Trombiculiasis in domestic goats and humans in the state of Maranhão, Brazil

“…After feeding and detachment, the mites molt to free-living nymphs and then to adults (JONES, 1950;SHATROV, 2000). Infestation by chigger mites causes severe itching as well as transmission of diseases like scrub typhus, which is caused by the intracellular parasite Orientia tsutsugamushi in southeastern Asia and the southwestern Pacific region (TAKAHASHI et al, 2004;CHOI et al, 2007). Likewise, in Spain, Fernández-Soto et al (2001) detected the bacterium Anaplasma phagocytophilum (cited as Ehrlichia phagocytophila) in larvae of Neotrombicula autumnalis (Shaw), before their contact with their hosts, thus suggesting that transovarian transmission of the pathogen occurs.…”