Yasuko K Yamada

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

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Publications (7)13.51 Total impact

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    ABSTRACT: Weak acid hypochlorous solution (WAHS) is known to have efficacy for inactivating pathogens and to be relatively safe with respect to the live body. Based on these advantages, many animal facilities have recently been introducing WAHS for daily cleaning of animal houses. In this study, we determined the effect of WAHS in inactivating specific pathogens of laboratory rodents and pathogens of opportunistic infection. WAHS with an actual chloride concentration of 60 ppm and a pH value of 6.0 was generated using purpose-built equipment. One volume of mouse hepatitis virus (MHV), Sendai virus, lymphocytic choriomeningitis virus, Bordetella bronchiseptica, Pasteurella pneumotropica, Corynebacterium kutscheri, Staphylococcus aureus, and Pseudomonas aeruginosa was mixed with 9 or 99 volumes of WAHS (×10 and ×100 reaction) for various periods (0.5, 1, and 5 min) at 25°C. After incubation, the remaining infectious viruses and live bacteria were determined by plaque assay or culture. In the ×100 reaction mixture, infectious viruses and live bacteria could not be detected for any of the pathogens examined even with the 0.5-min incubation. However, the effects for MHV, B. bronchiseptica, and P. aeruginosa were variable in the ×10 reaction mixture with the 0.5- and 1-min incubations. Sufficient effects were obtained by elongation of the reaction time to 5 min. In the case of MHV, reducing organic substances in the virus stock resulted in the WAHS being completely effective. WAHS is recommended for daily cleaning in animal facilities but should be used properly in order to obtain a sufficient effect, which includes such things as using a large enough volume to reduce effects of organic substances.
    Experimental Animals 01/2014; 63(2):141-7. · 1.46 Impact Factor
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    ABSTRACT: The aim of the present study was to determine the prevalence of infection by toxigenic Corynebacterium ulcerans in cynomolgus macaques (Macaca fascicularis) housed in an animal facility in Japan. Samples from the pharynges of animals from 2 closed colonies (colony A, n = 47; colony B, n = 21) were cultured. C. ulcerans grew from 43% and 47% of the samples from colonies A and B, respectively. The toxigenicity of these isolates was assessed by using PCR analysis for the diphtheria toxin gene and the Elek test and Vero cytotoxicity assay to detect diphtheria toxin. The proportion of macaques harboring toxigenic C. ulcerans was 6% in colony A and 29% in colony B. Analysis of diphtheria antitoxin neutralization titers in the sera revealed that 23% and 33% of macaques from colonies A and B, respectively, had a history of infection with toxigenic C. ulcerans. Pulsed-field gel electrophoresis of the toxigenic isolates showed that all of those recovered from macaques in colony B showed an identical genotype, suggesting that transmission of the organism occurred within the colony. However, isolates from colony A macaques showed 3 different genotypes, one of which was identical to the isolate from colony B. Additional studies evaluating the prevalence and transmission of toxigenic C. ulcerans within colonies of nonhuman primates are necessary to help control the spread of the infection. The current study is the first description of the isolation and characterization of toxigenic C. ulcerans from nonhuman primates in Japan.
    Comparative medicine 01/2013; 63(3):272-8. · 1.12 Impact Factor
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    ABSTRACT: We evaluated the in vitro efficacy of weak acid hypochlorous solution (WAHS) against murine norovirus (MNV) by plaque assay and compared the efficacy with diluted NaOCl (Purelox) and 70% ethanol. WAHS was as effective as 70% ethanol and diluted Purelox for 0.5-min reactions. For 0.5-min reactions in the presence of mouse feces emulsion, the efficacy of WHAS and 1:600 diluted Purelox was decreased, reducing the virus titers by 2.3 and 2.6 log10, respectively, while 70% ethanol reduced the titer by more than 5 log10. However, WAHS showed more than 5 log10 reductions for the 5-min reaction even in the presence of feces emulsion. Since WAHS showed enough efficacy in inactivating MNV in vitro, we tried to eliminate MNV from MNV-infected mice by substituting WAHS for their drinking water. However, MNV was found to be positive in feces of mice drinking WAHS by an RT-nested PCR and plaque assay. To investigate whether hypochlorite-based disinfectants could prevent infection of a mouse with MNV, WAHS or 1:6,000 diluted Purelox was substituted for the drinking water of mice for 2 or 4 weeks, and then the mice were placed in a cage with an MNV-infected mouse. The supply of disinfectants was continued after cohabitation, but MNV was detected in the feces of all the mice at 1 week after cohabitation. In this study, we tried to eliminate and prevent MNV infection from mice by supplying hypochlorite-based disinfectants as an easy and low-cost method. Unfortunately, drinking disinfectants was ineffective, so it is important to keep the facility environment clean by use of effective disinfectants. Also, animals introduced into facilities should be tested as MNV free by quarantine and periodically confirmed as MNV free by microbiological monitoring.
    Experimental Animals 01/2013; 62(3):237-45. · 1.46 Impact Factor
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    ABSTRACT: Although most inbred mouse strains are highly susceptible to mouse hepatitis virus (MHV) infection, the inbred SJL line of mice is highly resistant to its infection. The principal receptor for MHV is murine CEACAM1 (mCEACAM1). Susceptible strains of mice are homozygous for the 1a allele of mCeacam1, while SJL mice are homozygous for the 1b allele. mCEACAM1a (1a) has a 10- to 100-fold-higher receptor activity than does mCEACAM1b (1b). To explore the hypothesis that MHV susceptibility is due to the different MHV receptor activities of 1a and 1b, we established a chimeric C57BL/6 mouse (cB61ba) in which a part of the N-terminal immunoglobulin (Ig)-like domain of the mCeacam1a (1a) gene, which is responsible for MHV receptor function, is replaced by the corresponding region of mCeacam1b (1b). We compared the MHV susceptibility of these chimeric mice to that of SJL and B6 mice. B6 mice that are homozygous for 1a are highly susceptible to MHV-A59 infection, with a 50% lethal dose (LD(50)) of 10(2.5) PFU, while chimeric cB61ba mice and SJL mice homozygous for 1ba and 1b, respectively, survived following inoculation with 10(5) PFU. Unexpectedly, cB61ba mice were more resistant to MHV-A59 infection than SJL mice as measured by virus replication in target organs, including liver and brain. No infectious virus or viral RNA was detected in the organs of cB61ba mice, while viral RNA and infectious virus were detected in target organs of SJL mice. Furthermore, SJL mice produced antiviral antibodies after MHV-A59 inoculation with 10(5) PFU, but cB61ba mice did not. Thus, cB61ba mice are apparently completely resistant to MHV-A59 infection, while SJL mice permit low levels of MHV-A59 virus replication during self-limited, asymptomatic infection. When expressed on cultured BHK cells, the mCEACAM1b and mCEACAM1ba proteins had similar levels of MHV-A59 receptor activity. These results strongly support the hypothesis that although alleles of mCEACAM1 are the principal determinants of mouse susceptibility to MHV-A59, other as-yet-unidentified murine genes may also play a role in susceptibility to MHV.
    Journal of Virology 07/2010; 84(13):6654-66. · 5.08 Impact Factor
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    ABSTRACT: An enzyme-linked immunosorbent assay (ELISA) was developed to detect the antibody against lymphocytic choriomeningitis virus (LCMV) in sera of laboratory animals. In this ELISA system, LCMV-nucleoprotein (NP) expressed by recombinant baculovirus and purified with high molar urea was used as the antigen. Sera from laboratory animals experimentally infected with the Armstrong strain or the newly isolated M1 strain of LCMV were examined to detect anti-LCMV antibody by the ELISA system, and the reactivity was compared with that of IFA test. Regardless of LCMV strain, all the sera of adult mice infected with LCMV were positive with very high optical density (OD). Also, the sera from mice neonatally infected with LCMV M1 strain were positive with slightly lower OD than adult mice. In contrast, all the sera of uninfected mice were negative to LCMV-NP antigen. Similarly, anti-LCMV antibodies were detected in all the sera of hamsters, mastomyses, and gerbils infected with the LCMV Armstrong strain. The results of the ELISA were in complete agreement with those of IFA, and indicate the high sensitivity and specificity of the ELISA system in the detection of anti-LCMV antibody. Because this ELISA system does not require handling infectious LCMV in the course of the antigen preparation and serological assay, there is no risk of contamination in the laboratory or nearby animal facility. In addition, by using negative control antigen in parallel with positive antigen in ELISA, we can exactly check the LCMV contamination in laboratory animals.
    Experimental Animals 07/2008; 57(4):357-65. · 1.46 Impact Factor
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    ABSTRACT: Persistent LCMV infection in wild-derived MAI/Pas mice housed under conventional conditions remained undetected for a decade, despite periodic health monitoring using dirty-bedding sentinels. When MAI/Pas mice were rederived by embryo transfer, recipient mothers produced antiLCMV antibodies, which first revealed the presence of the virus in the colony. Before this information was obtained, MAI/Pas mice had been shipped to another facility, undergone cesarean rederivation there, and been introduced into the recipient barrier. The foster mothers of rederived pups were LCMV-negative according to enzyme-linked immunosorbent assay, but sera of both cesarean-rederived MAI/Pas mice and their foster mothers were positive for LCMV infection by immunofluorescent assay (IFA). LCMV was isolated from the MAI/Pas mice, and its genomic RNA was sequenced. Examination of animal technicians in contact with LCMV-infected mice and of other mouse samples by IFA or a reverse transcriptase-polymerase chain reaction test (or both) revealed that neither the workers nor other animals had been infected with LCMV. Experimental data showed that LCMV transmission from persistently infected mice to naïve ones occurred only after direct contact of animals housed in the same cage. This experience demonstrates the importance of careful viral monitoring in the transfer of laboratory rodents between institutions, the limitation of dirty-bedding sentinels for detection of LCMV infection, and the inadequacy of cesarean rederivation for elimination of enzootic LCMV infection. 111
    Comparative medicine 07/2007; 57(3):272-81. · 1.12 Impact Factor
  • Advances in experimental medicine and biology 02/2006; 581:519-22. · 1.83 Impact Factor