Geographical Distribution and Epidemiologic Factors of Chigger Mites on Apodemus agrarius during Autumn in Korea

A nationwide survey of chigger mites causing scrub typhus and an investigation of epidemiologic factors for chigger mites was conducted at 16 localities in 8 provinces in Korea during autumn 2009, 2012, and 2013. A total of 233 Apodemus agrarius were captured, and all were infested with chigger mites. The chigger index was highest in Chungcheongbuk-do in 2009 (358.3) and 2012 (290.1) and Chungcheongnam-do in 2013 (294.4). The predominant chigger mite species was Leptotrombidium pallidum in the northern and central parts and L. scutellare in the southern and western parts, Korea. L. pallidum was not found in Jellanam-do and Gyeongsangnam-do and the distribution of L. scutellare had been expanded in the northern parts of Korea. The chigger index of L. pallidum was positively correlated with temperature and negatively correlated with humidity. The incidence of scrub typhus is dependent on L. scutellare index. These findings could be helpful to monitor the distribution of chigger mites and to develop a preventive measures for scrub typhus in Korea.

Monthly Occurrence of Vectors and Reservoir Rodents of Scrub Typhus in an Endemic Area of Jeollanam-do, Korea

Monthly surveys were conducted to investigate the occurrence of chigger mites and seroprevalence of scrub typhus among small mammals in Jeollanam-do, the southwestern part of Korea, from November 2006 through October 2007. Fifty-eight small mammals, including 57 Apodemus agrarius (98.3%) and 1 Crocidura lasiura (1.7%), were captured, and a total of 4,675 chigger mites representing 4 genera and 8 species were collected from them. The chigger infestation rate among small mammals was 69.0%. The most predominant species in A. agrarius was Leptotrombidium scutellare (54.0%), followed by Leptotrombidium pallidum (39.4%), Leptotrombidium orientale (4.4%), Leptotrombidium palpale (1.1%), Neotrombicula tamiyai (0.6%), Eushoengastia koreaensis (0.3%), Neotrombicula gardellai (0.3%), and Cheladonta ikaoensis (<0.1%). The chigger index of A. agrarius was the highest in October (740.0), followed by November (242.0), September (134.6), March (98.3), February (38.2), January (35.3), December (34.5), April (30.8), and May (1.7). The average antibody positive rate of scrub typhus in wild rodents was 50.0%. The seropositive rates were high in October (100.0%) and November (83.3%), whereas those in other months were relatively low (28.6-57.1%). The chigger index of L. scutellare rapidly increased in September to form an acuminate peak in October, followed by a gradual decline. These results suggest that the outbreak of scrub typhus in the southwestern part of Korean peninsula is mostly due to L. scutellare.

Geographical Distribution and Relative Abundance of Vectors of Scrub Typhus in the Republic of Korea

A survey to determine the geographical distribution and relative abundance of potential vectors of scrub typhus was conducted from October to November 2006 at 13 localities throughout the Republic of Korea. Apodemus agrarius accounted for 97.6% (80/82) of all rodents, while only 2 Myodes regulus (2/82) were collected. A total of 10,860 chiggers were collected from A. agrarius belonging to 4 genera and 8 species, while only Walchia fragilis (40) was collected from Myodes regulus. Leptotrombidium pallidum (8,137; 74.9%), a vector of scrub typhus, was the predominant species collected from A. agrarius followed by Leptotrombidium scutellare (2,057, 18.9%), Leptotrombidium palpale (279; 2.7%), Leptotrombidium orientale (232; 2.1%), and Leptotrombidium zetum (79; 0.7%), Neotrombicula tamiyai (58; 0.5%), Euschoengastica koreaensis (16; 0.1%), and Cheladonta ikaoensis (2; < 0.1%). L. pallidum was the predominant chigger collected at collection sites in Gangwon (100%), Gyeonggi (87.2%), Chungnam (100%), Chungbuk (100%), Jeonbuk (73.9%), Jeonnam (77.0%), and Gyeongbuk (66.1%) provinces, whereas L. scutellare was the predominant chigger collected in Gyeongnam province (77.9%) and Jeju Island (62.3%). Data suggest a correlation between chigger population abundance and human cases of scrub typhus in Korea.

Comparative Study of Retinal Tissues of Genus Zacco and Genus Pseudogobio in Korean Fish: Possible Relationship with Prey and Habitat / 대한해부학회지

This study was performed to investigate whether the kinds and arrangement patterns of the cone cells were related to the kinds of behavior, prey and habitat in the species of genus Zacco and genus Pseudogobio The retinas were observed by a light microscopy using H-E staining method. The cone cells of Z. platypus and Z. temmincki showed compact mosaic patterns of row type. Keep apart from the center, the diameters of the double and single cone cells were gradually increased. Z. temmincki developed the identical double cone cells, and Z. platypus developed the non-identical double and single cone cells. But, Pseudogobio esocinus constituted loose mosaic patterns of row and irregular types and developed the identical double cones and single cone cells. The above results suggest that the kinds and mosaic pattern of cone cells of Z. temmincki feeding on a moving aquatic insects in relative limpid water and swift current, reflect the highest resolution among these three species. And the kinds and mosaic pattern of cone cells of P. esocinus keep watching around in the sand ground and feeding on a moving aquatic insects in relative limpid water and gentle current, suggest that if has better resolution than those of Z. platypus feeding on mainly adhesive algae and some aquatic insects in slightly turbid water.

Lens Characterization of Genus Zacco and Pseudogobio in Korean Fish / 체질인류학회지

There are many modifications of eye shape and structure among fish, the general plan is similar throughout. This study was performed to comparative investigation for the lens shape and the interlocking pattern of lens fiber in genus Zacco (Z. temmincki and Z. platypus) and Pseudogobio (P. esocinus). The equatorial and axis diameter of lens for the classification of lens shape were measured by micrometer. And the interlocking patterns of lens fibers were observed by scanning electron microscopy (SEM). The lens shapes of Z. platypus and Z. temmincki were spherical (axis /equqtorial diameter = 1), but the lens shape of P. esocinus was subspherical type (axis / equqtorial diameter = 0.87). The interlocking patterns of lens fibers showed that Z. temmincki have an "anchor and socket" connection, Z. platy-pus have a "ball and socket" connection, and P. esocinus have a "rod and socket" connection. The results of this study may be utilized in the taxonomic keys for the classification of fish.

Electron Microscopic Autoradiographic Study on the Secretion of Atrial Specific Granules from Atrial Cardiocytes in Dehydrated Rats / 대한해부학회지

This study was performed to investigate for the effect of dehydration on the synthesis, secretion and secreted pathway of atrial specific granules contained ANP by electron microscopic autoradiography. Male Sprague-Dawley rats, body weigh of about 50 g (range 47 to 53 g), were divided into control, 1 day dehydration and 3 days dehydration groups. Each group was divided into four groups according to sacrificed time on 20 min, 60 min and 240 min after the injection of L-leucine 3 H. Tissues of the right atrium obtained from animals were processed for typical electron microscopic procedure, and then embedded in Epon 812. Ultrathin sections were followed for electron microscopic autoradiographic method. Atrial specific granules were various in size, and some granules had a lower electron densities and indistinct granular membrane in the dehydration groups compared with the control group. In the electron microscopic autoradiographs of atrial wall, silver grains indicated by means of the positions of labelled L-leucine 3 H over the cell inclusion included atrial specific granules, cell organelles, intercellular spaces and blood vesseles. In the control group, high specific radioactivity was observed in the Golgi apparatus at 20 min, and in the rough endoplasmic reticulums and atrial specific granules at 60 min after the injection of L-leucine3H. And high level of radioactivities were observed in the cell membranes and blood vesseles at 240 min after the injection of L-leucine3H. In the 1 day and 3 days dehydration groups, radioactivities of Golgi apparatus, atrial specific granules, cell membranes and intercellular spaces were high level at 20 min, and radioactivities of rough endoplasmic reticulums and blood vesseles were high level at 60 min after isotope injection. Stored atrial specific granules were increased to 34.1% in the 1 day dehydration group, 27.4% in the 3 days dehydration group compared with the control group. In the 3 days dehydration group, newly formed granules increased 85.02% at 20 min, but those decreased rapidly to 36.87% at 60 min, 20.45% at 240 min after the injection of L-leucine3H in atrial cardiocytes. This results suggest that total ANP increased rapidly in the atrial cardiocytes, and newly formed ANP secreted rapidly into the intercellular space in the condition of dehydration, and ANP from atrial cardiocytes remain in intercellular space for dehydration period.