Evaluation of Francisella tularensis ΔpdpC as a candidate live attenuated vaccine against respiratory challenge by a virulent SCHU P9 strain of Francisella tularensis in a C57BL/6J mouse model.

Francisella tularensis, which causes tularemia, is an intracellular gram-negative bacterium. F. tularensis has received significant attention in recent decades because of its history as a biological weapon. Thus, development of novel vaccines against tularemia has been an important goal. The attenuated F. tularensis strain ΔpdpC, in which the pathogenicity determinant protein C gene (pdpC) has been disrupted by TargeTron mutagenesis, was investigated as a potential vaccine candidate for tularemia in the present study. C57BL/6J mice immunized s.c. with 1 × 106 CFUs of ΔpdpC were challenged intranasally with 100× the median lethal dose (LD50 ) of a virulent SCHU P9 strain 21 days post immunization. Protection against this challenge was achieved in 38% of immunized C57BL/6J mice administered 100 LD50 of this strain. Conversely, all unimmunized mice succumbed to death 6 days post challenge. Survival rates were significantly higher in vaccinated than in unimmunized mice. In addition, ΔpdpC was passaged serially in mice to confirm its stable attenuation. Low bacterial loads persisted in mouse spleens during the first to tenth passages. No statistically significant changes in the number of CFUs were observed during in vivo passage of ΔpdpC. The inserted intron sequences for disrupting pdpC were completely maintained even after the tenth passage in mice. Considering the stable attenuation and intron sequences, it is suggested that ΔpdpC is a promising tularemia vaccine candidate.

Antigen capture ELISA system for henipaviruses using polyclonal antibodies obtained by DNA immunization.

A novel antigen-capture sandwich ELISA system targeting the glycoproteins of the henipaviruses Nipah virus (NiV) and Hendra virus (HeV) was developed. Utilizing purified polyclonal antibodies derived from NiV glycoprotein-encoding DNA-immunized rabbits, we established a system that can detect the native antigenic structures of the henipavirus surface glycoproteins using simplified and inexpensive methods. The lowest detection limit against live viruses was achieved for NiV Bangladesh strain, 2.5 × 10(4) TCID(50). Considering the recent emergence of genetic variants of henipaviruses and the resultant problems that arise for PCR-based detection, this system could serve as an alternative rapid diagnostic and detection assay.

Effect of cellular cholesterol depletion on rabies virus infection.

Although there are several reports on candidates for rabies virus (RABV) receptor, possible roles played by these receptor candidates in determination of highly neurotropic nature of RABV have not been well understood. Since these candidate receptors for RABV were reported to be frequently associated with cholesterol-rich microdomains characterized by lipid rafts and caveolae structures, we attempted to determine whether the disturbance of microdomains caused by the cholesterol depletion showed any effects on RABV infection. When the cellular cholesterol was depleted by methyl-beta-cyclodextrin (MBCD) treatment, increase in RABV adsorption and infection, but not multiplication rather than suppression was observed in both BHK-21 and HEp-2 cells. These effects exerted by MBCD treatment on RABV infection could be reversed by cholesterol reconstitution. These results suggest that RABV enters BHK-21 or HEp-2 cells through ports of entry other than those located on cholesterol-rich microdomains and raise the possibility that RABV uses different mechanisms to enter the non-neuronal cells.

Detection and phylogenetic analysis of phlebovirus, including severe fever with thrombocytopenia syndrome virus, in ticks collected from Tokyo, Japan.

Severe fever with thrombocytopenia syndrome (SFTS) was detected for the first time in China in 2011. Since then, human cases have been reported in endemic regions, including Japan. To investigate the presence of tick-borne pathogens in Tokyo, 551 ticks (266 samples) were collected from October 2015 to October 2016. Although the SFTS virus was not detected by RT-PCR, a novel phlebovirus was detected in one sample. In a phylogenetic analysis based on the partial nucleotide sequences of the L and S segments of the virus, the virus clustered with Lesvos virus (Greece), Yongjia tick virus, and Dabieshan tick virus (China). Further studies involving virus isolation are required to characterize this novel phlebovirus and to expand the epidemiological knowledge of related pathogens.

Seroepidemiology of non-primate hepacivirus (NPHV) in Japanese native horses.

Non-primate hepacivirus (NPHV) is recently identified as a closely related homologue of hepatitis C virus. The previous studies showed a high prevalence of NPHV infection among Japanese domestic horses originated from abroad. The historical distribution of NPHV among horses in Japan, therefore, is still unknown. In this study, seroepidemiological study of NPHV was conducted using 335 sera from five breeds of Japanese native horses. These horses are maintained as the pedigree and are reared apart from other horse breeds. The detection of antibodies against NPHV were conducted by western blot analysis using the recombinant protein of the NPHV core protein. The antibodies against NPHV were detected in all five breeds, 83 out of 335 (23.4%) horses. These results suggested that NPHV was circulating among Japanese native horses.

Multiple polymerase gene mutations for human adaptation occurring in Asian H5N1 influenza virus clinical isolates.

The role of the influenza virus polymerase complex in host range restriction has been well-studied and several host range determinants, such as the polymerase PB2-E627K and PB2-D701N mutations, have been identified. However, there may be additional, currently unknown, human adaptation polymerase mutations. Here, we used a database search of influenza virus H5N1 clade 1.1, clade 2.3.2.1 and clade 2.3.4 strains isolated from 2008-2012 in Southern China, Vietnam and Cambodia to identify polymerase adaptation mutations that had been selected in infected patients. Several of these mutations acted either alone or together to increase viral polymerase activity in human airway cells to levels similar to the PB2-D701N and PB2-E627K single mutations and to increase progeny virus yields in infected mouse lungs to levels similar to the PB2-D701N single mutation. In particular, specific mutations acted synergistically with the PB2-D701N mutation and showed synergistic effects on viral replication both in human airway cells and mice compared with the corresponding single mutations. Thus, H5N1 viruses in infected patients were able to acquire multiple polymerase mutations that acted cooperatively for human adaptation. Our findings give new insight into the human adaptation of AI viruses and help in avian influenza virus risk assessment.

Role of GPI-anchored NCAM-120 in rabies virus infection.

Although the neural cell adhesion molecule (NCAM) -140 and -180 have been shown to serve as a receptor for rabies virus (RV), it was not known whether the other major isoform of NCAM, GPI-anchored NCAM-120 functions as RV receptor. In this study, we have established HEp-2 cells stably expressing NCAM-120 or NCAM-140, and their susceptibilities to RV infection were compared. The results demonstrated that NCAM-120 served as virus attachment protein; however, the cells expressing NCAM-120 did not support efficient RV replication. Furthermore, the level of IFN-ss mRNA was apparently elevated in NCAM-120 expressing cells but not in NCAM-140 expressing cells, suggesting that GPI-anchored NCAM-120 suppressed RV replication via induction of IFN-ss even though NCAM-120 was able to promote virus penetration into the cells.

Transition of the intestinal microbiota of cats with age.

The transition of intestinal microbiota with age has been well described in humans. However, the age-related changes in intestinal microbiota of cats have not been well studied. In the present study, we investigated the composition of intestinal microbiota of cats in 5 different age groups (pre-weanling, weanling, young, aged, senile) with a culture-based method. For lactobacilli and bifidobacteria, we also quantified with molecular-based method, real-time PCR. The results suggested that the composition of the feline intestinal microbiota changes with age, while the changes were different from those of humans and dogs. Bifidobacteria which are predominant in human intestine or lactobacilli which are predominant in dog intestine, did not appear to be important in cat intestines. Enterococci, instead, seem to be major lactic acid producing bacteria in cats. We also identified lactobacilli and bifidobacteria at the species level based on 16S rRNA gene sequences and found that the species composition of Lactobacillus also changed with age.

The genotypes of Orientia tsutsugamushi, identified in scrub typhus patients in northern Vietnam.

Background: There are an estimated one million patients with scrub typhus in the Asia-Pacific region. There are few reports describing the incidence of scrub typhus in Vietnam. Methods: Blood samples collected from 63 patients clinically diagnosed as having scrub typhus from July 2015 to September 2016 were subjected to genotyping of Orientia tsutsugamushi. Results and Conclusions: Of these patients, 42 (67%) tested positive for O. tsutsugamushi, and the most common genotype was identified to be Karp (55%). Other genotypes, TA763, Gilliam type in Japan variant, and Kato were also found in 17%, 17% and 12% of patients, respectively. To better understand the epidemiological landscape of scrub typhus in Vietnam, a countrywide study is needed. Accession numbers: LC110330-LC110333, LC110336-LC110351 and LC214804-LC214825.

Epizootiological study of rodent-borne hepatitis E virus HEV-C1 in small mammals in Hanoi, Vietnam.

There is concern about the zoonotic potential of rodent-borne hepatitis E virus, designated as HEV-C1. However, epizootiological information about HEV-C1 is limited. To address this issue, serum samples from 443 small mammals captured at 5 sites in Hanoi, Vietnam, were examined for anti-HEV-C1 IgG antibodies. In addition, livers of seropositive animals were examined for viral RNA. Anti-HEV-C1 antibodies were detected in 57 (12.9%) of the 443 serum samples. Seropositive animals were found in all of the sites (4.7% to 22.2%). Anti-HEV-C1 antibodies were detected from 48 (12.3%) of 389 Rattus norvegicus and 9 (19.6%) of 46 R. tanezumi, but were not detected from 8 Suncus murinus. Viral RNAs were detected from 13 (22.8%) of the 57 seropositive rodents. The detection rate of viral RNA in seropositive R. tanezumi (66.7%, 6/9) was significantly higher than that in seropositive R. norvegicus (14.6%, 7/48). The results suggest that R. tanezumi is more susceptible than R. norvegicus to HEV-C1 infection. Phylogenetic analysis revealed that Vietnamese strains were divided into 3 clusters in genetic group 2 of HEV-C1. Multiple clusters of viruses were detected at several sites without species specificity, suggesting that 3 clusters of HEV-C1 co-circulate in Hanoi, Vietnam.

Prevalence and Phylogenetic Analysis of Orientia tsutsugamushi in Small Mammals in Hanoi, Vietnam.

Rodents are important reservoirs of many human pathogens transmitted via arthropod vectors. Arthropod-borne bacteria belonging to the family Rickettsiaceae cause acute febrile diseases in humans worldwide, but the real burdens of rickettsial diseases appear to be underestimated in Hanoi, Vietnam, because differential diagnosis on the basis of clinical signs and symptoms is confounded by the presence of other tropical infectious diseases with similar signs and symptoms. To know the prevalence of bacteria of the family Rickettsiaceae among small mammals in Hanoi, 519 animals thriving in the public places were captured and examined for the presence of bacterial sequences using duplex PCR. Nucleotide sequences specific for Orientia tsutsugamushi were detected in seven samples (1.3%). Out of seven animals, two were captured in a market, whereas five were in hospitals. None of the captured small mammals tested positive for the genus Rickettsia. The nucleotide sequence analysis of the genes encoding the 47-kDa high-temperature requirement A (47-kDa HtrA) and 56-kDa type-specific antigen (TSA) showed that these seven isolates were indistinguishable from each other. O. tsutsugamushi isolated in this study was closely related phylogenetically to the Gilliam strain, which was originally isolated at the border of Assam and Burma, rather than to those isolated in the central to southern part of Vietnam. It should be emphasized that Vietnamese hospitals were heavily infested by small rodents and some of them harbored O. tsutsugamushi. Strict hygienic control should be implemented to mitigate the potential risk posed by O. tsutsugamushi in hospital settings.

A novel immunochromatographic system for easy-to-use detection of group 1 avian influenza viruses with acquired human-type receptor binding specificity.

A switch of viral hemagglutinin receptor binding specificity from bird-type α2,3- to human-type α2,6-linked sialic acid is necessary for an avian influenza virus to become a pandemic virus. In this study, an easy-to-use strip test to detect receptor binding specificity of influenza virus was developed. A biotinylated anti-hemagglutinin antibody that bound a broad range of group 1 influenza A viruses and latex-conjugated α2,3 (blue) and α2,6 (red) sialylglycopolymers were used in an immunochromatographic strip test, with avidin and lectin immobilized on a nitrocellulose membrane at test and control lines, respectively. Accumulation of a sialylglycopolymer-virus-antibody complex at the test line was visualized by eye. The strip test could be completed in 30min and did not require special equipment or skills, thereby avoiding some disadvantages of current methods for analyzing receptor binding specificity of influenza virus. The strip test could detect the receptor binding specificity of a wide range of influenza viruses, as well as small increases in the binding affinity of variant H5N1 viruses to α2,6 sialylglycans at viral titers >128 hemagglutination units. The strip test results were in agreement with those of ELISA virus binding assays, with correlations >0.95. In conclusion, the immunochromatographic strip test developed in this study should be useful for monitoring potential changes in the receptor binding specificity of group 1 influenza A viruses in the field.

Antibody survey on avian influenza viruses using egg yolks of ducks in Hanoi between 2010 and 2012.

In Vietnam, numerous surveillance programs are conducted to monitor the prevalence of avian influenza (AI) viruses. Three serological methods-the agar-gel immunodiffusion test, hemagglutination inhibition (HI) test, and enzyme-linked immunosorbent assay-are well established for detection of AI virus antibodies in poultry sera. Several recent reports have validated egg yolk as an alternative source for detection of AI virus antibodies. In this study, we investigated AI virus antibodies in ducks by HI testing using egg yolk. Ten duck eggs were collected every month from 10 randomly selected markets in Hanoi from April 2010 to March 2012. The HI test was performed using low pathogenic avian influenza (LPAI) viruses (H3, H4, H6, H7, H9, and H11 subtypes) and highly pathogenic avian influenza (HPAI) viruses (H5N1 clade 2.3.4 and 2.3.2.1) as antigens. HI testing for H3, H6, and H9 was 29% positive in November 2010, 50% positive in October and November 2010, and 12% positive in June 2011. These results indicated that several epidemics of LPAI viruses had occurred during the study period. In addition, antibodies against H7 were negative. The results of HI testing for H5N1 showed that the reactivity of the dominant HI antibody shifted from H5N1 clade 2.3.4 to clade 2.3.2.1. In conclusion, egg yolk is useful for long term monitoring of AI virus antibodies and the use of egg-based antibody detection may contribute to improvements in animal welfare.

Isolation and characterization of H6N1 and H9N2 avian influenza viruses from Ducks in Hanoi, Vietnam.

We report the genetic characterization of low pathogenic avian influenza (LPAI) viruses isolated from domestic ducks in northern Vietnam in 2009. In total, 22 influenza A viruses consisting of 21 H6N1 subtypes and one H9N2 subtype were isolated from 1488 ducks collected in February, March, and April 2009, accounting the overall virus isolation rate for 1.5%. No H5N1 strain was isolated in this study. Phylogenetic analysis indicated that all the eight genes of the H6N1 and H9N2 subtypes analyzed in this study were similar to those isolated in Korea, southeast China and northern Japan, and wild birds which migrate along the coastal East Asian Flyway are estimated to transmit these viruses. There was no evidence that the H6N1 and H9N2 subtypes share the gene segments with H5N1 subtypes. However, it is important to monitor the prevalence and genetical backgrounds of LPAI viruses among poultry in an area where several different influenza A subtypes are in circulation.

Second generation of pseudotype-based serum neutralization assay for Nipah virus antibodies: sensitive and high-throughput analysis utilizing secreted alkaline phosphatase.

Nipah virus (NiV), Paramyxoviridae, Henipavirus, is classified as a biosafety level (BSL) 4 pathogen, along with the closely related Hendra virus (HeV). A novel serum neutralization test was developed for measuring NiV neutralizing antibodies under BSL2 conditions using a recombinant vesicular stomatitis virus (VSV) expressing secreted alkaline phosphatase (SEAP) and pseudotyped with NiV F/G proteins (VSV-NiV-SEAP). A unique characteristic of this novel assay is the ability to obtain neutralization titers by measuring SEAP activity in supernatant using a common ELISA plate reader. This confers a remarkable advantage over the first generation of NiV-pseudotypes expressing green fluorescent protein or luciferase, which require expensive and specific measuring equipment. Using panels of NiV- and HeV-specific sera from various species, the VSV-NiV-SEAP assay demonstrated neutralizing antibody status (positive/negative) consistent with that obtained by conventional live NiV test, and gave higher antibody titers than the latter. Additionally, when screening sixty-six fruit bat sera at one dilution, the VSV-NiV-SEAP assay produced identical results to the live NiV test and only required a very small amount (2µl) of sera. The results suggest that this novel VSV-NiV-SEAP assay is safe, useful for high-throughput screening of sera using an ELISA plate reader, and has high sensitivity and specificity.

Inhibition of rabies virus propagation in mouse neuroblastoma cells by an intrabody against the viral phosphoprotein.

Rabies virus (RABV) is highly neurotropic and causes acute infection of the central nervous system. Death can be averted by prompt post-exposure prophylaxis; however, after clinical symptoms appear, the mortality rate is almost 100% and no reliable treatment is available. In this study, we investigated whether intracellular immunization using single-chain variable fragments (scFvs) against RABV phosphoprotein (RABV-P) could inhibit RABV propagation in neuronal cells. Of four scFv clones derived from an scFv phage-displayed library, scFv-P19 showed extremely high transfection efficiency and stable expression in mouse neuroblastoma (MNA) cells. The intracellular affinity and inhibition of RABV propagation were investigated using RABV-infected MNA cells pretransfected with the scFv-P19 gene. The specific interaction between scFv and RABV-P was confirmed by an immunoprecipitation assay and an indirect immunofluorescence assay showing that these molecules colocalized in the cytoplasm. Measurements of the spread of RABV in a culture well and the virus titer in the supernatant showed that RABV inhibition peaked 3 days after infection, at 98.6% and 99.9% inhibition, respectively. Although the mechanism of RABV inhibition by scFv-P19 is not clear, this scFv-based intracellular immunization could be a candidate for future RABV therapeutic studies if combined with appropriate delivery and application systems.

A neutralization test for specific detection of Nipah virus antibodies using pseudotyped vesicular stomatitis virus expressing green fluorescent protein.

Nipah virus (NiV) is a new zoonotic paramyxovirus that emerged in 1998 and is now classified in the genus Henipavirus along with the closely related Hendra virus (HeV). NiV is highly pathogenic in several vertebrate species including humans, and the lack of available vaccines or specific treatment restricts it to biosafety level 4 (BSL4) containment. A serum neutralization test was developed for measuring NiV neutralizing antibodies under BSL2 conditions using a recombinant vesicular stomatitis virus (VSV) expressing green fluorescent protein (GFP) and bearing the F and G proteins of NiV (VSV-NiV-GFP). The neutralization titers were obtained by counting GFP-expressing cells or by measuring fluorescence. The performance of this new assay was compared against the conventional test using live NiV with panels of sera from several mammalian species, including sera from NiV outbreaks, experimental infections, as well as HeV-specific sera. The results obtained with the VSV-NiV-GFP based test correlated with those obtained using live NiV. Using a 50% reduction in VSV-NiV-GFP infected cells as the cut-off for neutralization, this new assay demonstrated its potential as an effective tool for detecting NiV neutralizing antibodies under BSL2 containment with greater speed, sensitivity and safety as compared to the conventional NiV serum neutralization test.