M Takahashi

National Institute of Infectious Diseases, Tokyo, Edo, Tōkyō, Japan

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Publications (25)32.96 Total impact

  • The Veterinary record 05/2004; 154(15):471-2. · 1.80 Impact Factor
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    ABSTRACT: Parasitological and histopathological examinations were performed in 25 raccoon dogs (Nyctereutes procyonoides) obtained in Kanagawa Prefecture, Japan, all of which were found to be heavily infected with Sarcoptes scabiei. The mites detected on these raccoon dogs were morphologically indistinguishable from the human species, and no Demodex mites were detected. Histopathological examinations showed prominent hyperkeratosis and acanthosis with eczema, and numerous burrows containing mites were observed in the epidermis. The enzootic dermatitis of wild raccoon dogs in recent years was clearly demonstrated to be caused by S. scabiei in the present study.
    Journal of Veterinary Medical Science 05/2001; 63(4):457-60. · 0.88 Impact Factor
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    ABSTRACT: There are various antigenic variants of Orientia tsutsugamushi which are distinguished by immunological and molecular genetic methods targeted at the antigenic diversity of 56-kDa type-specific antigen proteins. The present study was performed to analyze 15 strains successfully isolated from rodents in Saitama Prefecture, Japan, by 56-kDa gene sequence homologies, reactivities with type-specific monoclonal antibodies and polymerase chain reaction (PCR) using type-specific primer-pairs. We demonstrated the presence of a new type of O. tsutsugamushi among the isolates. This new type, designated as the Saitama type, was located in the branch of Karp type in the phylogenetic tree based on 56-kDa gene sequences, but distant from the known Karp types, such as Karp, JP-1 and JP-2, showing less than 90% homology. Strains of this type could not be distinguished by immunological methods from Karp type strains, but a new primer-pair for PCR which specifically amplifies the DNA of this new type strain was designed. This primer-pair may serve to find this strain type in future studies.
    Microbiology and Immunology 02/2001; 45(6):439-46. · 1.55 Impact Factor
  • Journal of Invertebrate Pathology 08/1998; 72(1):93-5. · 2.67 Impact Factor
  • Parasitology International - PARASITOL INT. 01/1998; 47:331-331.
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    ABSTRACT: In colonies of Leptotrombidium fletcheri mites infected with Orientia tsutsugamushi (Ot), the agent of scrub typhus, males rarely appear. In the present study, the development of a high ratio of males was observed after introduction of minocycline (MC). A high dose of MC was injected subcutaneously into a mouse, and by feeding unfed larvae from an infected mite colony on this mouse, the Ot in the mites were successfully killed. Of a total of 130 unfed larvae attached to the mouse, 29 developed into females; of these, 9 laid an average of 112.4 eggs/female. Unfed larvae in the succeeding generations were attached to untreated mice. All adults in the P and F1 generation were females, and males started to appear at the F2 generation. The ratio of males to females was 332:7, 108:13, 263:61 and 71:9 at the F2, F3, F4 and F5 generations, respectively. These data suggest that Ot in the ovary or gonad may suppress the development of males.
    European Journal of Epidemiology 02/1997; 13(1):79-86. · 5.12 Impact Factor
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    ABSTRACT: Proton Nuclear Magnetic Resonance (1H-NMR) Analysis of insect cell culture media used for cultivating insect cell lines derived from the fleshfly Sarcophaga peregrina, swallowtail butterfly Papilio xuthus, and cabbage armyworm Mamestra brassicae revealed that ethanol appeared in the medium as the cultures aged. By incorporating [13C-1]-glucose into the media, we pursued 13C-NMR spectrograms to show that the ethanol was derived from glucose. Thus, it became evident that the insect cells cultured in vitro produce ethanol from glucose as a metabolite.
    In Vitro Cellular & Developmental Biology - Animal 01/1996; 31(11):876-9. · 1.29 Impact Factor
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    ABSTRACT: Engorged larvae of Leptotrombidium akamushi (Brumpt), a vector of scrub typhus, were reared in small plastic containers placed on the ground and fed fresh eggs of the collembolan Sinella curviseta Brook. Engorged larvae obtained in October developed into deutonymphs through protonymphs approximately 1 mo before winter and became dormant in the cold winter season (approximately 3 mo). Most deutonymphs developed into tritonymphs in April and adults in May. Females began laying eggs in mid-June and the numbers of unfed larvae showed a peak in August. The mites reared from July rapidly developed into adults by August, and laid eggs in September. Larvae were most abundant in October, and adults became dormant in the winter. The same adults laid eggs from early May to late June and, upon hatching, the larval population peaked in early July of the 2nd summer. Most larvae died before the 2nd winter. Eggs hatched approximately 3 wk after oviposition and longevity of unfed larvae was 2 mo. Because of this very short incubation period, L. akamushi larvae occur in the summer, whereas L. pallidum Nagayo, Miyagawa, Mitamura & Tamiya, and L. scutellare Nagayo, Miyagawa, Mitamura, Tamiya & Tenjin occur in the autumn, although 3 species lay eggs from May to August.
    Journal of Medical Entomology 12/1995; 32(6):843-6. · 1.86 Impact Factor
  • H Urakami, M Takahashi, M Murata, A Tamura
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    ABSTRACT: Leptotrombidium pallidum naturally infected with Rickettsia tsutsugamushi was reared and bred in our laboratory for several generations by brother and sister mating. The larvae and adults at the 8th and 9th generations were sectioned and observed by electron microscopy for analysis for the distribution of rickettsiae in the mites. The distribution densities of rickettsiae were markedly different among organs in each mite, but rickettsiae were seen in all the organs and tissues. Rickettsiae were distributed in the highest density in the salivary gland of larvae, and in the salivary gland, excretory bladder, epidermal layer, ovary and testis of adult mites. Only a few rickettsiae were recognized in the muscle of both larvae and adults. On the other hand, we found, in the infected family line used, a significant number of mites in which no rickettsiae were found by electron microscopy. The grouping of rickettsia-positive and -negative mites according to the parent family revealed that the efficiency of vertical transmission of rickettsia was different from one parent family to another. Thus, it became clear that a significant number of rickettsia-negative mites are produced in an infected family line.
    Japanese journal of medical science & biology 07/1994; 47(3):127-39.
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    ABSTRACT: Proton nuclear magnetic resonance (1H NMR) spectroscopy was used to characterize the oxidized products in the serum lipoprotein lipids (LPL) of rabbits infected with Schistosoma japonicum. The loss of bis-allylic and allylic methylenes proton peaks (2.7 and 2.0 p.p.m.) of unsaturated systems of the LPL and the appearance of the signals of the conjugated diene systems of hydroperoxide (5.43-6.45 p.p.m.) and epidioxide (2.45 p.p.m.) of the fatty chains of the serum demonstrated the lipids degradation associated with the Schistosoma infection.
    International Journal for Parasitology 06/1994; 24(3):417-9. · 3.64 Impact Factor
  • H Urakami, M Takahashi, E Hori, A Tamura
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    ABSTRACT: Rickettsia tsutsugamushi in Leptotromibidium pallidum was observed by electron microscopy and rickettsiae were found in the various tissues and organs of both larvae and adults. Budding of rickettsiae, a manner of release from the host cells, was observed only in the rudiments of the reproductive organs in larvae. Oogonia and maturing oocytes in adult females and eggs after oviposition contained the microorganisms. In adult males, rickettsiae were also found in the spermatogonia, spermatocytes, and spermatids in the early stage of spermatogenesis, but were eliminated from these cells during maturation. Only the maturing spermatids, but not the eliminated rickettsiae, migrated to another rickettsia-free area of the testis, resulting in the separation of spermatids from rickettsiae and in the production of rickettsia-free spermatophores. Based on these observations, the mechanism of vertical transmission of the rickettsiae to the progeny occurs only in the female parents. Most rickettsiae in the somatic cells of larvae and adults were coccoid, but some rickettsiae in the ovary and the testis of adult mites showed bacillary forms and were enveloped by a membrane of unknown origin.
    The American journal of tropical medicine and hygiene 03/1994; 50(2):219-28. · 2.53 Impact Factor
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    ABSTRACT: Larvae of Leptotrombidium pallidum (Nagayo, Miyagawa, Mitamura & Tamiya) from uninfected laboratory colonies were fed on mice infected with Rickettsia tsutsugamushi (Hayashi) Ogata. Infection of the chiggers with R. tsutsugamushi was determined by passage of chigger exudates into ddY mice. The passage method was modified so that an inoculum was considered to be positive when R. tsutsugamushi or anti-R. tsutsugamushi antibody, or both, were detected in mice up to the third blind passage. R. tsutsugamushi was detected in six of 18 larvae (33.3%) and in all developmental stages. In adults, five of 18 males and 10 of 46 females were infected with R. tsutsugamushi. In L. fuji (Kuwata, Berge & Philip), R. tsutsugamushi was not found in 57 engorged larvae fed on rickettsemic mice but was found in a very low percentage of deutonymphs and adults. Female L. pallidum from larvae fed on infected mice were paired individually, and F1 larvae were collected. Although eight females were found to be positive for R. tsutsugamushi, the rickettsia was not detected in 12 pools (249 larvae) of F1 larvae from these infected females. We concluded that uninfected mites became infected by feeding on rickettsemic mice at comparatively high rates depending on the species and transmitted this infection transstadially to succeeding life stages, but not vertically to larvae in the following F1 generation.
    Journal of Medical Entomology 03/1994; 31(2):212-6. · 1.86 Impact Factor
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    ABSTRACT: Male adults of Periplaneta americana were graded into three groups according to their flight activity; very active (continuous flight longer than 5 min), active (1–5 min) and inactive (shorter than 1 min). 1H-NMR analysis showed that approx. 30 mM trehalose was present in the haemolymph of each of the above categories of untreated cockroaches. After exhaustive flight, the haemolymph trehalose concentration in very active individuals decreased to <10 mM. When validoxylamine A, which is reported to be a potent and specific inhibitor of trehalase in various organisms, was injected into the cockroaches, they were unable to continue flying for >2.5 min. The trehalase activity of the flight muscle was inhibited about 70% and the haemolymph trehalose concentration increased to about 3 times the normal level without change in the other haemolymph components. Trehalose also accumulated in the tissues of the cockroaches injected with validoxylamine A. These observations suggest that validoxylamine A inhibits the muscle trehalase and prevents the use of trehalose as a source of energy for flight.
    Journal of Insect Physiology - J INSECT PHYSIOL. 01/1994; 40(6):455-461.
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    ABSTRACT: Engorged larvae of Leptotrombidium pallidum Nagayo, Miyagawa, Mitamura & Tamiya, the vector mite of scrub typhus in Japan, were reared by feeding them with fresh eggs of the collembolan Sinella curviseta Brook while confined in small plastic containers under natural conditions in a copse. The larvae were collected from wild rodents (Apodemus speciosus) in autumn 1985 and spring 1986. Adults were kept alive for 2 yr or longer. The larvae obtained in autumn became dormant in the cold winter season, and growth recommenced in the spring. Thus, the development of mites collected in April became synchronized with that of larvae obtained in the autumn. Most larvae developed into protonymphs in May, deutonymphs in June, tritonymphs in July, and adults in August. The females laid eggs in two consecutive summers. Some larvae collected in autumn were kept in a refrigerator until the following summer. They developed into deutonymphs, tritonymphs, or adults and then became dormant in the winter. Development restarted the next spring and all became adult by summer, when the females laid eggs. Under experimental conditions, all larvae are hatched in the autumn, unlike the natural situation in which two peaks of larval occurrence on wild rodents are observed in autumn and spring.
    Journal of Medical Entomology 04/1993; 30(2):320-5. · 1.86 Impact Factor
  • Entomologia Experimentalis Et Applicata - ENTOMOL EXP APPL. 01/1993; 66(3):269-274.
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    ABSTRACT: In the epidemiological surveys on scrub typhus at Chichibu City near Tokyo, an area, 350 m by 35 m, in the Hitsujiyama Park was found to be heavily infested with Rickettsia tsutsugamushi (Rt). Distribution of trombiculid mites and their infection rates in this area were studied using sentinel animals, 48 Microtus montebelli and 10 ddY mice. The surveys were conducted 6 times in the autumn in 1985 and 1986. At the first 2 surveys, 16 animals were placed at random, and 4 restricted areas were identified as highly populated with trombiculid mites. For the detailed survey, each of 4 areas was divided into 2 m x 2 m quadrats to settle a sentinel animal to each. A total of mites collected by all sentinel animals was 331 Leptotrombidium pallidum, 175 L. fuji and 16 Gahrliepia saduski. Almost all mites were collected by M. montebelli, except only 1 L. fuji in 10 mice. From a M. montebelli in a quadrat, 157 L. pallidum were recovered, whereas the number/vole was 0 to 24 in the others. L. fuji was also highly aggregated at 2 sites. Rt was detected from individual mites by avidin-biotin immunofluorescence or isolated by the mouse passage from individual or pooled mites. Only Karp strain of Rt was detected or isolated from L. pallidum at a ratio of 31/286 (10.8%). No Rt was found from L. fuji or G. saduski. The infection rate in L. pallidum was especially high in 3 voles at ratios of 6/11, 2/5 and 3/5, respectively. Out of 14 sentinel M. montebelli with infected L. pallidum, 12 (85.7%) were infected with Rt. It was concluded that L. pallidum was distributed in aggregated clusters to form the mite islands and was infected heavily at the specific sites to make the infective spots.
    The Japanese journal of experimental medicine 01/1991; 60(6):325-35.
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    ABSTRACT: Transmission of Rickettsia tsutsugamushi (Rt) from a rodent to trombiculid mites was studied. Wild rodents, Apodemus speciosus, were subcutaneously inoculated with Karp strain of Rt, and larval trombiculid mites were released on the ear lobes for feeding, 10 and 20 days after infection. Isolation of Rt was performed from individual mites or pools of 2 to 7 mites by the mouse passage method. From Apodemus 10 days after Rt infection, possibly at the time of high rickettsiaemia, the infection rates among mites were 4/44 (9.1%) or higher in Leptotrombidium fuji, 1/20 (5%) in L. pallidum and 0/41 in L. deliense. From Apodemus 20 days after infection, no mite was infected in 50 L. fuji or 7 L. pallidum possibly due to reduced rickettsiaemia. Transmission of Rt from rodent to mite was proven to occur at low probability on appropriate conditions but not by the incidental chance.
    The Japanese journal of experimental medicine 09/1990; 60(4):203-8.
  • The Japanese journal of experimental medicine 09/1990; 60(4):241-5.
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    ABSTRACT: In an attempt to study nitrogen metabolism in a parasite, we applied 15N-nuclear magnetic resonance (NMR) technology with a stable isotope, a 15N-labeled compound, for the study of the transamination system in A. cantonensis eggs, and demonstrated that 15N-aspartic acid can serve as an amino group donor for both the 2-oxoglutaric-glutamic acid and the pyruvic acid-alanine transamination systems in the eggs.
    International Journal for Parasitology 03/1990; 20(1):131-2. · 3.64 Impact Factor
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    ABSTRACT: 13C-nuclear magnetic resonance (NMR) spectroscopy was used to identify metabolites excreted by Angiostrongylus cantonensis eggs which had been maintained aerobically in the presence of D-[13C6] glucose. Using 13C-NMR we proved that lactate, acetate and alanine originated from glucose present in the medium via glycolysis. Aminooxyacetate, an inhibitor of alanine transferase, inhibited simultaneously alanine production and the ability to take up glutamate, aspartate and valine from the medium. In addition, we demonstrated that these amino acids can serve as amino group donors of the pyruvate to alanine transamination system in the eggs.
    Physiological chemistry and physics and medical NMR 02/1989; 21(2):165-70.