Luck Ju Baek

Tick-Borne Rickettsial Pathogens in Ticks and Small Mammals in Korea

ABSTRACT In order to investigate the prevalence of tick-borne infectious agents among ticks, ticks comprising five species from two genera (Hemaphysalis spp. and Ixodes spp.) were screened using molecular techniques. Ticks (3,135) were collected from small wild-caught mammals or by dragging/flagging in the Republic of Korea (ROK) and were pooled into a total of 1,638 samples (1 to 27 ticks per pool). From the 1,638 tick samples, species-specific fragments of Anaplasma phagocytophilum (1 sample), Anaplasma platys (52 samples), Ehrlichia chaffeensis (29 samples), Ehrlichia ewingii (2 samples), Ehrlichia canis (18 samples), and Rickettsia rickettsii (28 samples) were amplified by PCR assay. Twenty-one pooled and individual tick samples had mixed infections of two (15 samples) or three (6 samples) pathogens. In addition, 424 spleen samples from small captured mammals (389 rodents, 33 insectivores, and 2 weasels) were screened for selected zoonotic pathogens. Species-specific DNA fragments of A. phagocytophilum (110 samples), A. platys (68 samples), E. chaffeensis (8 samples), E. ewingii (26 samples), E. canis (51 samples), and Rickettsia sp. (22 samples) were amplified by PCR assay. One hundred thirty small mammals had single infections, while 4, 14, and 21 striped field mice (Apodemus agrarius) had mixed infections of four, three, and two pathogens, respectively. Phylogenetic analysis based on nucleotide sequence comparison also revealed that Korean strains of E. chaffeensis clustered closely with those from China and the United States, while the Rickettsia (rOmpA) sequences clustered within a clade together with a Chinese strain. These results suggest that these agents should be considered in differential diagnosis while examining cases of acute febrile illnesses in humans as well as animals in the ROK.

Inhibitory Effect of Breast Milk on Infectivity of Live Oral Rotavirus Vaccines

Background: Live oral rotavirus vaccines have been less immunogenic and efficacious among children in poor developing countries compared with middle income and industrialized countries for reasons that are not yet completely understood. We assessed whether the neutralizing activity of breast milk could lower the titer of vaccine virus and explain this difference in vitro. Methods: Breast milk samples were collected from mothers who were breast-feeding infants 4 to 29 weeks of age (ie, vaccine eligible age) in India (N = 40), Vietnam (N = 77), South Korea (N = 34), and the United States (N = 51). We examined breast milk for rotavirus-specific IgA and neutralizing activity against 3 rotavirus vaccine strains—RV1, RV5 G1, and 116E using enzyme immunoassays. The inhibitory effect of breast milk on RV1 was further examined by a plaque reduction assay. Findings: Breast milk from Indian women had the highest IgA and neutralizing titers against all 3 vaccine strains, while lower but comparable median IgA and neutralizing titers were detected in breast milk from Korean and Vietnamese women, and the lowest titers were seen in American women. Neutralizing activity was greatest against the 2 vaccine strains of human origin, RV1 and 116E. This neutralizing activity in one half of the breast milk specimens from Indian women could reduce the effective titer of RV1 by ∼2 logs, of 116E by 1.5 logs, and RV5 G1 strain by ∼1 log more than that of breast milk from American women. Interpretation: The lower immunogenicity and efficacy of rotavirus vaccines in poor developing countries could be explained, in part, by higher titers of IgA and neutralizing activity in breast milk consumed by their infants at the time of immunization that could effectively reduce the potency of the vaccine. Strategies to overcome this negative effect, such as delaying breast-feeding at the time of immunization, should be evaluated.

Thottapalayam Virus, a Prototype Shrewborne Hantavirus

This virus is antigenically and phylogenetically distinct from rodent-borne hantaviruses.

Molecular epidemiology of hepatitis A virus in Korea

Background: The prevalence of antibodies for hepatitis A virus (anti‐HAV) in adolescents and young adults has decreased remarkably following the economic growth in Korea. As a result, this age group has a high risk for HAV infection paradoxically, and over 1500 cases of clinically overt hepatitis A occurred in 1998. Human isolates of hepatitis A virus (HAV) are categorized within four genotypes (I, II, III, and VII). In some geographic regions, closely related isolates cluster, suggesting endemic spread of the virus, while in other regions multiple genotypes circulate. Virtually no data are available with regard to the genetic relatedness of Korean strains of HAV.

Effects of Endocytosis Inhibitory Drugs on Rubella Virus Entry into VeroE6 Cells

It has been suggested that infectious entry of rubella virus (RV) is conducted by receptor mediated endocytosis. To explore the cellular entry mechanism of RV, inhibitory effects of drugs affecting various endocytic pathways on RV entry into VeroE6 cells were analyzed. Results showed that RV infectious entry into VeroE6 cells is mediated by clathrin‐dependent endocytosis and not by caveolae‐mediated endocytosis. Moreover, chemical inhibition of macropinocytosis such as treatments of amiloride, actin and microtubule‐disrupting drug significantly reduced RV infection. Considering that macropinocytosis is inducible endocytosis by cellular stimulations, clathrin‐mediated endocytosis is likely to be a major route of RV infectious entry.

Characterization of tula virus from common voles (Microtus arvalis) in Poland: Evidence for geographic-specific phylogenetic clustering

Tula virus (TULV), a recently identified arvicolid rodent-borne hantavirus, is harbored by the European common vole (Microtus arvalis) in Central Russia and the Czech and Slovak Republics. We report the isolation and characterization of this hantavirus from M. arvalis captured in Poland, a country where human disease caused by hantaviruses has not been recognized. Of 34 arvicolid rodents (24 Clethrionomys glareolus, 9 M. arvalis, 1 Pitymys sp.) captured in Lodz and Tuszyn, Poland, during June to September 1995, sera from 3 M. arvalis and 3 C. glareolus contained IgG antibodies to Puumala virus (PUUV), as determined by an indirect immunofluorescent antibody assay. Alignment and comparison of the 1852-nucleotide S segment and a 1676-nucleotide region of the G2 glycoprotein-encoding M segment, amplified from lung tissues of two hantavirus-seropositive M. arvalis, revealed 83.9–85.2% and 82.3–83.5% sequence similarity, respectively, with TULV strains from Central Russia and the Czech and Slovak Republics. A > 98% sequence conservation was found at the amino acid level. Phylogenetic analysis indicated that the newly found TULV strains from Poland were closely related to, but distinct from, TULV from elsewhere in Europe.

Divergent ancestral lineages of newfound hantaviruses harbored by phylogenetically related crocidurine shrew species in Korea

Spurred by the recent isolation of a novel hantavirus, named Imjin virus (MJNV), from the Ussuri white-toothed shrew (Crocidura lasiura), targeted trapping was conducted for the phylogenetically related Asian lesser white-toothed shrew (Crocidura shantungensis). Pair-wise alignment and comparison of the S, M and L segments of a newfound hantavirus, designated Jeju virus (JJUV), indicated remarkably low nucleotide and amino acid sequence similarity with MJNV. Phylogenetic analyses, using maximum likelihood and Bayesian methods, showed divergent ancestral lineages for JJUV and MJNV, despite the close phylogenetic relationship of their reservoir soricid hosts. Also, no evidence of host switching was apparent in tanglegrams, generated by TreeMap 2.0β.

Phylogenetic Analysis of the Small Hydrophobic (SH) Gene of Mumps Virus in Korea: Identification of a New Genotype

Viral RNAs extracted from fifteen mumps virus isolated from throat swab, saliva, blood, urine or CSF during mumps epidemics between 1997–1998 in Korea were amplified by reverse transcriptase‐polymerase chain reaction (RT‐PCR) and compared by nucleotide sequencing of the small hydrophobic (SH) gene. The deduced amino acid sequences of the SH gene were aligned with the published sequences of mumps virus isolated in different geographic areas. A comparison of the SH gene of mumps viruses in Korea indicated 96.2–100% and 91.2–100% similarity at the nucleotide and amino acid levels, respectively. Phylogenetic analysis, using the neighbor‐joining method, showed that Korean mumps virus strains formed a genetically distinct monophyletic group from previously reported genotypes based on the 315‐bp length nucleotide and 57 deduced amino acid sequences of the SH gene, and possibly be designated as a new genotype (I).

Genetic Diversity of Apodemus agrarius-Borne Hantaan Virus in Korea

Hantaan (HTN) virus, the etiologic agent of clinically severe hemorrhagic fever with renal syndrome (HFRS), was first isolated in 1976 from lung tissues of striped field mice (Apodemus agrarius) captured in Songnae-ri, Kyungki-do, Korea. To clarify the genetic diversity and phylogenetic relationship among Korean strains of HTN virus, viral sequences of the partial S and M segments were amplified from lung tissues of 24 seropositive striped field mice captured between 1989 and 1998 at 11 sites in South Korea. The 771-nucleotide (nt) S segment sequences (coordinates 432 to 1202) of HTN virus strains from Yangju-kun differed by 10 to 40 nt (1.3 to 5.2%) from virus strains from Pocheon-kun, Songnae-ri and Nonsan-kun. Similar degrees of genetic variation were found in the G1 and G2 glycoprotein-encoding M segment. Phylogenetic trees, based on the partial S and M segments and generated by the maximum parsimony and neighbor-joining methods, demonstrated that virus strains from various geographic regions in South Korea showed a tendency to form two phylogenetic subgroups and were evolutionarily distinct from HTN virus strains from the People’s Republic of China.

Ecological surveillance of small mammals at Firing Points 10 and 60, Gyeonggi Province, Republic of Korea, 2001–2005

Abstract Throughout Korea, small mammals are hosts to a number of disease-causing agents that pose a health threat to U.S. and Korean military forces while they conduct field-training exercises. A seasonal rodent-borne disease surveillance program was established at two firing points (FP), FP-10, and FP-60, and conducted over five years from 2001 through 2005 in response to hantavirus cases among U.S. soldiers. The ecology of these sites consisted primarily of tall grasses associated with semi-permanent and temporary water sources (drainage ditches and a small stream) and dry-land agriculture farming. Eight species of rodents and one species of insectivore were collected, including Apodemus agrarius, Micromys minutus, Mus musculus, Rattus norvegicus, Tscherskia triton, Microtus fortis, Myodes regulus, and Crocidura lasiura. The striped field mouse, A. agrarius, (primary reservoir for Hantaan virus, the causative agent of Korean hemorrhagic fever), was the most frequently collected, representing 90.6% of the 1,288 small mammals captured at both sites. Reported herein are the ecological parameters, seasonal population densities, and seasonal population characteristics associated with small mammals collected at two military training sites in the Republic of Korea.