Hitoko Misumi

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.

Stylostome organization in feeding Leptotrombidium larvae (Acariformes: Trombiculidae)

The stylostome of larvae of the trombiculids Leptotrombidium scutellare (Nagayo et al.), Leptotrombidium fletcheri (Womersley et Heaslip) and Leptotrombidium deliense (Walch) was studied experimentally at different time intervals after larval attachment using the histological method. The stylostome of these species has the same organization and belongs to the epidermal combined with the mixed type, developing more in width than in length. Neither transverse nor conspicuous longitudinal layers are present within the stylostome walls, which stain predominantly in red with Azan, also showing longitudinal portions with blue staining. Larvae tend to attach closely to each other and scabs, consisting of the hyperkeratotic epidermal layers fusing with migrating inflammatory cells, develop around the attachment sites. The dermis shows inflammatory foci with dilated capillaries and inflammatory cells inserting in the connective tissue layer underneath the stylostome. The feeding cavity, which is moderately expressed, may be found either in the epidermis or in the dermis. It contains inflammatory cells and their debris in the liquefied host tissues. The stylostome length depends on the character of the attachment site (the thicker epidermis or scab the longer the stylostome), and does not directly correspond to the stages of larval feeding. Nevertheless, at the 48-h time interval, nearly all attached larvae are found to be fully fed and their midgut cells are filled with nutritional globules.

Ixodes philipi: Redescription of Female and First Description of Male, with Records from Streaked Shearwater in Japan (Acarina: Ixodidae)

Abstract Ixodes philipi Keirans & Kohls, 1970 is so far known only from two female specimens taken from the streaked shearwater, Puffinus leucomelas (Temminck, 1835) [presently Calonectris leucomelas (Temminck, 1835)], or the madeiran storm-petrel, Oceanodroma castro (Harcourt, 1851), in Japan. We redescribe the female and describe the male of this species. We used nine adults (four males and five females) taken from the bodies of C. leucomelas and/or soil samples of their nest burrows in Japan, indicating that C. leucomelas is the main natural host bird of I. philipi.

Mouthparts in Leptotrombidium larvae (Acariformes: Trombiculidae)

Mouthparts of Leptotrombidium larvae (Acariformes: Trombiculidae), potential vectors of tsutsugamushi disease agents, were studied in detail using light microscopy, scanning electron microscopy, and transmission electron microscopy. The mouthparts incorporated within the pseudotagma gnathosoma are composed of the infracapitulum ventrally and the chelicerae dorsally. The ventral wall of the infracapitulum is formed by a wide mentum posteriorly and a narrowed malapophysis anteriorly. The malapophysis firmly envelops the distal cheliceral portions by its lateral walls. The lateral lips of the malapophysis are flexible structures hiding the cheliceral blades in inactive condition and turning back forming a type of temporary sucker closely applied to the host skin during feeding. The roof of the infracapitulum is formed by a weakly sclerotized labrum anteriorly and a cervix with the capitular apodemes extending posteriorly. The labral muscles are lacking. The capitular apodemes serve as origin for pharyngeal dilators running to the dorsal wall of the pharynx fused with the bottom of the infracapitulum. The basal cheliceral segments are separated from each other besides the very posterior portions where they are movably joined by the inner walls. The sigmoid pieces serve for insertion of the cheliceral elevators originating at the posterior portions of the basal segments. The movable digits reveal the solid basal sclerite and the cheliceral blade curved upward with a tricuspid cap on its tip. Dendrites of nerve cells run along the digits to their tips. The ganglia are placed within the basal segments just behind the movable digits. The chelicerae also reveal well developed flexible fixed digits overhanging the basal portions of the blades. The gnathosoma possesses several sets of extrinsic muscles originating at the scutum and at the soft cuticle behind it. Laterally, the gnathosoma bears five‐segmented palps with a trifurcate palpal claw. J. Morphol. 277:424–444, 2016.

First record in Japan of tortoise tick Amblyomma Geoemydae (Cantor 1847) (Acari: Ixodidae) parasitizing Pryer’s keelback snake Hebius Pryeri (Boulenger, 1887) (Reptile: Colubridae)

ABSTRACT Two larvae of tortoise tick Amblyomma geoemydae (Acari: Ixodidae) were collected from the fresh remains of a Pryer’s keelback snake Hebius pryeri (Boulenger, 1887), likely dead from accidental causes at the Kunigami-son in northern Okinawa Island, Okinawa Prefecture, Japan. This is the first such host record for A. geoemydae in Japan. Based on this finding, we have updated the available collection records of ticks found on Japanese snakes.

Chromosome studies of Leptotrombidium akamushi and L. scutellare (Acari: Trombiculidae) in Japan

Abstract The karyotypes of the two main scrub typhus vectors, Leptotrombidium akamushi (Brumpt) and L. scutellare (Nagayo, Miyagawa, Tamiya and Tenjin), in Japan were studied in order to determine the sex mechanism. The mite tritonymph was found the most suitable stage for the chromosome preparations. At this stage, mitotic cell divisions were found among the spermatogenetic cells in the male, while only mitotic cells were found in the female. Their karyotypes were 2n = 12+XY in L. akamushi and 2n = 14+XY in L. scutellare, respectively.