Double-stranded RNA stimulates chemokine expression in microglia through vacuolar pH-dependent activation of intracellular signaling pathways

During neurotropic virus infection, microglia act as a source of chemokines, thereby regulating the recruitment of peripheral leukocytes and the multicellular immune response within the CNS. Herein, we present a comprehensive study on the chemokine production by microglia in response to double-stranded RNA (dsRNA), a conserved molecular pattern of virus infection. Transcriptional analyses of chemokine genes revealed that dsRNA strongly induces the expression of CXC chemokine ligand 10 (CXCL10) and CC chemokine ligand 5 (CCL5) in microglia. We also observed that the dsRNA stimulation triggered the activation of signaling pathways mediated by nuclear factor kappaB (NF-kappaB) and mitogen-activated protein kinases (MAPK), including extracellular signal-regulated kinases 1 and 2 (ERK1/2), p38, and c-Jun N-terminal kinase (JNK). The microglial CXCL10 response to dsRNA was induced via NF-kappaB, p38, and JNK pathways, whereas the dsRNA-induced CCL5 production was dependent on JNK, but not on the other signal-transducing molecules tested. In addition, the acidic environment of intracellular vesicles was required for the activation of cellular signaling in response to dsRNA. Taken together, these results suggest that the recognition of dsRNA structure selectively induces the CXCL10 and CCL5 responses in microglia through vacuolar pH-dependent activation of NF-kappaB and MAPK signaling pathways.

[West Nile fever and West Nile encephalitis]

West Nile virus is a mosquito-borne flavivirus, and maintained in mosquito-bird cycle in nature. Humans are a dead-end host in West Nile virus infection. Symptoms are developed in approximately 20% of West Nile virus-infected humans. Encephalitis and meningitis are developed in about 1 out of 150 infected humans, especially in elderly populations. It has recently been reported that West Nile virus causes polio-like, acute flaccid paralysis and polyneuritis. These symptoms occur in patients without central nervous system symptoms as well as in those with encephalitis. Thus, West Nile virus causes various types of illness in humans. West Nile virus has not entered Japan yet. However, West Nile virus should be considered to be one of the causative agents for patient with a febrile illness, meningitis, encephalitis or acute flaccid paralysis who came back from West Nile endemic or epidemic areas of the world.

Nineteen nucleotides in the variable region of 3' non-translated region are dispensable for the replication of dengue type 1 virus in vitro

In many flaviruses, first 50-400 nucleotides of 3' non-translated region (3' NTR) exhibit lower conservation level than other regions and are called "variable region". Two dengue type 1 virus (DENV-1) strains, which have 17- and 29-nt deletion in the variable region, were recently isolated from Japanese dengue fever patients. The effect of a small deletion in the 3' NTR was analyzed using two DENV-1 viruses which were prepared from a newly developed infectious cDNA clone. These included a recombinant virus rDENV-1(02-20), without any deletion in 3' NTR, and rDENV-1m10, with 19-nt deletion in the variable region of rDENV-1(02-20). These two viruses were compared for growth kinetics and plaque morphology in Vero, Huh-7 and C6/36 cells. No apparent difference was detected between rDENV-1(02-20) and rDENV-1m10 in replication efficiency and plaque size in these cell lines. The results suggest that the complete variable region of DENV-1 is dispensable for virus replication and propagation in vitro.

An attenuated LC16m8 smallpox vaccine: analysis of full-genome sequence and induction of immune protection

The potential threat of smallpox bioterrorism has made urgent the development of lower-virulence vaccinia virus vaccines. An attenuated LC16m8 (m8) vaccine was developed in 1975 from the Lister strain used in the World Health Organization smallpox eradication program but was not used against endemic smallpox. Today, no vaccines can be tested with variola virus for efficacy in humans, and the mechanisms of immune protection against the major intracellular mature virion (IMV) and minor extracellular enveloped virion (EEV) populations of poxviruses are poorly understood. Here, we determined the full-genome sequences of the m8, parental LC16mO (mO), and grandparental Lister (LO) strains and analyzed their evolutionary relationships. Sequence data and PCR analysis indicated that m8 was a progeny of LO and that m8 preserved almost all of the open reading frames of vaccinia virus except for the disrupted EEV envelope gene B5R. In accordance with this genomic background, m8 induced 100% protection against a highly pathogenic vaccinia WR virus in mice by a single vaccination, despite the lack of anti-B5R and anti-EEV antibodies. The immunogenicity and priming efficacy with the m8 vaccine consisting mainly of IMV were as high as those with the intact-EEV parental mO and grandparental LO vaccines. Thus, mice vaccinated with 10(7) PFU of m8 produced low levels of anti-B5R antibodies after WR challenge, probably because of quick clearance of B5R-expressing WR EEV by strong immunity induced by the vaccination. These results suggest that priming with m8 IMV provides efficient protection despite undetectable levels of immunity against EEV.

Rabies virus-induced activation of mitogen-activated protein kinase and NF-kappaB signaling pathways regulates expression of CXC and CC chemokine ligands in microglia

Following virus infection of the central nervous system, microglia, the ontogenetic and functional equivalents of macrophages in somatic tissues, act as sources of chemokines, thereby recruiting peripheral leukocytes into the brain parenchyma. In the present study, we have systemically examined the growth characteristics of rabies virus (RV) in microglia and the activation of cellular signaling pathways leading to chemokine expression upon RV infection. In RV-inoculated microglia, the synthesis of the viral genome and the production of virus progenies were significantly impaired, while the expression of viral proteins was observed. Transcriptional analyses of the expression profiles of chemokine genes revealed that RV infection, but not exposure to inactivated virions, strongly induces the expression of CXC chemokine ligand 10 (CXCL10) and CC chemokine ligand 5 (CCL5) in microglia. RV infection triggered the activation of signaling pathways mediated by mitogen-activated protein kinases, including p38, extracellular signal-regulated kinases 1 and 2 (ERK1/2), and c-Jun N-terminal kinase, and nuclear factor kappaB (NF-kappaB). RV-induced expression of CXCL10 and CCL5 was achieved by the activation of p38 and NF-kappaB pathways. In contrast, the activation of ERK1/2 was found to down-regulate CCL5 expression in RV-infected microglia, despite the fact that it was involved in partial induction of CXCL10 expression. Furthermore, NF-kappaB signaling upon RV infection was augmented via a p38-mediated mechanism. Taken together, these results indicate that the strong induction of CXCL10 and CCL5 expression in microglia is precisely regulated by the activation of multiple signaling pathways through the recognition of RV infection.

Antigen-capture enzyme-linked immunosorbent assay for the diagnosis of crimean-congo hemorrhagic fever using a novel monoclonal antibody

An antigen-capture enzyme-linked immunosorbent assay (ELISA) was developed for the diagnosis of Crimean-Congo hemorrhagic fever (CCHF) using a novel monoclonal antibody, 1B7, to the recombinant nucleoprotein (rNP) of CCHF virus (CCHFV) Chinese strain 8402. This ELISA detected at least 2 ng/100 microl of CCHFV rNP of 8402 and of the Nigeria strain Ibr 10200, and also detected authentic nucleoproteins (NP) of Chinese strains. Although the sensitivity of the ELISA was lower than that of nested reverse transcription polymerase chain reaction (RT-PCR), it was able to detect nucleoproteins in acute sera of CCHF patients. The presence of anti-CCHFV IgG decreased the sensitivity of the ELISA, possibly due to competition with 1B7, and this would tend to limit application of the ELISA. However, the method may be useful for the diagnosis of CCHF patients in the acute stage of illness, especially in laboratories not equipped with RT-PCR testing capabilities.

Detection of Japanese encephalitis (JE) virus-specific IgM in cerebrospinal fluid and serum samples from JE patients

Detection of Japanese encephalitis virus (JEV)-specific IgM by IgM-capture enzymed-linked immunosorbent assay (IgM-capture ELISA) has been accepted as the standard for serological diagnosis. In the present study, we analyzed the time course of the positive rate of JEV-specific IgM in serum and cerebrospinal fluid (CSF) specimens from confirmed JE patients. Serum and CSF samples were obtained from 155 JE cases for diagnostic purposes at hospitals in Thailand from 2002 to 2004. The levels of specific IgM were assessed by IgM-capture ELISA in the 171 serum and 156 CSF samples. Anti-JEV IgM was detected in 26 of 44 serum samples collected on days 1-4 of the disease period, in 31 of 44 samples collected on days 5-8, in 23 of 26 samples collected on days 9-12, and in all the samples collected on day 13 or later. Specific IgM was detected in 60 of 66 CSF samples collected on days 1-4 of illness, and in all the CSF samples but one collected on day 7 or later. The results indicate that the detection of JEV-specific IgM in CSF by IgM-capture ELISA is a reliable laboratory diagnostic method for confirmation of JE throughout the disease period, while the detection of IgM in serum samples is a reliable method on day 9 or later.

Vesicular stomatitis virus pseudotyped with severe acute respiratory syndrome coronavirus spike protein

Severe acute respiratory syndrome coronavirus (SARS-CoV) contains a single spike (S) protein, which binds to its receptor, angiotensin-converting enzyme 2 (ACE2), induces membrane fusion and serves as a neutralizing antigen. A SARS-CoV-S protein-bearing vesicular stomatitis virus (VSV) pseudotype using the VSVDeltaG* system was generated. Partial deletion of the SARS-CoV-S protein cytoplasmic domain allowed efficient incorporation into VSV particles and led to the generation of a pseudotype (VSV-SARS-St19) at high titre. Green fluorescent protein expression was demonstrated as early as 7 h after infection of Vero E6 cells with VSV-SARS-St19. VSV-SARS-St19 was neutralized by anti-SARS-CoV antibody and soluble ACE2, and its infection was blocked by treatment of Vero E6 cells with anti-ACE2 antibody. These results indicated that VSV-SARS-St19 infection is mediated by SARS-CoV-S protein in an ACE2-dependent manner. VSV-SARS-St19 will be useful for analysing the function of SARS-CoV-S protein and for developing rapid methods of detecting neutralizing antibodies specific for SARS-CoV infection.

Characterization of monoclonal antibodies to Marburg virus nucleoprotein (NP) that can be used for NP-capture enzyme-linked immunosorbent assay

After the first documented outbreak of Marburg hemorrhagic fever identified in Europe in 1967, several sporadic cases and an outbreak of Marburg hemorrhagic fever have been reported in Africa. In order to establish a diagnostic system for Marburg hemorrhagic fever by the detection of Marburg virus nucleoprotein, monoclonal antibodies to the recombinant nucleoprotein were produced. Two clones of monoclonal antibodies, MAb2A7 and MAb2H6, were efficacious in the antigen-capture enzyme-linked immunosorbent assay (ELISA). At least 40 ng/ml of the recombinant nucleoprotein of Marburg virus was detected by the antigen-capture ELISA format. The epitope of the monoclonal antibody (MAb2A7) was located in the carboxy-terminus of nucleoprotein from amino acid position 634 to 647, while that of the MAb2H6 was located on the extreme region of the carboxy-terminus of the Marburg virus nucleoprotein (amino acid position 643-695). These monoclonal antibodies strongly interacted with the conformational epitopes on the carboxy-terminus of the nucleoprotein. Furthermore, these two monoclonal antibodies were reacted with the authentic Marburg virus antigens by indirect immunofluorescence assay. These data suggest that the Marburg virus nucleoprotein-capture ELISA system using the monoclonal antibodies is a promising technique for rapid diagnosis of Marburg hemorrhagic fever.

Persisting humoral antiviral immunity within the Japanese population after the discontinuation in 1976 of routine smallpox vaccinations

Concerns have arisen recently about the possible use of smallpox for a bioterrorism attack. Routine smallpox vaccination was discontinued in Japan in 1976; however, it is uncertain exactly how long vaccination-induced immunity lasts. We sought to evaluate the seroprevalence and intensity of anti-smallpox immunity among representatives of the present Japanese population. The subjects included 876 individuals who were born between 1937 and 1982. Vaccinia virus-specific immunoglobulin G (IgG) levels were measured by enzyme-linked immunosorbent assay (ELISA), and 152 of 876 samples were also tested for the presence of neutralizing antibodies. Of the subjects who were born before 1962, between 1962 and 1968, and between 1969 and 1975, 98.6, 98.6, and 66.0%, respectively, still retained the vaccinia virus-specific IgG with ELISA values for optical density at 405 nm (OD(405)) of > or = 0.10. The corresponding figures for retained IgGs with OD405 values of > or = 0.30 were 91.0, 90.3, and 58.2%, respectively. Neutralizing antibodies were also maintained. The sera with OD(405) values of > or = 0.30 showed 89% sensitivity and a 93% positive predictive value for detection of neutralizing antibodies (> or = 4). Thus, approximately 80% of persons born before 1969 and 50% of those born between 1969 and 1975 were also found to have maintained neutralizing antibodies against smallpox. A considerable proportion of the previous vaccinated individuals still retain significant levels of antiviral immunity. This long-lasting immunity may provide some protective benefits in the case of reemergence of smallpox, and the disease may not spread as widely and fatally as generally expected.

JNK and PI3k/Akt signaling pathways are required for establishing persistent SARS-CoV infection in Vero E6 cells

Persistence was established after most of the SARS-CoV-infected Vero E6 cells died. RNA of the defective interfering virus was not observed in the persistently infected cells by Northern blot analysis. SARS-CoV diluted to 2 PFU failed to establish persistence, suggesting that some particular viruses in the seed virus did not induce persistent infection. Interestingly, a viral receptor, angiotensin converting enzyme (ACE)-2, was down-regulated in persistently infected cells. G418-selected clones established from parent Vero E6 cells, which were transfected with a plasmid containing the neomycin resistance gene, were infected with SARS-CoV, resulting in a potential cell population capable of persistence in Vero E6 cells. Our previous studies demonstrated that signaling pathways of extracellular signal-related kinase (ERK1/2), c-Jun N-terminal protein kinase (JNK), p38 mitogen-activated protein kinase (MAPK), and phosphatidylinositol 3'-kinase (PI3K)/Akt were activated in SARS-CoV-infected Vero E6 cells. Previous studies also showed that the activation of p38 MAPK by viral infection-induced apoptosis, and a weak activation of Akt was not sufficient to protect from apoptosis. In the present study, we showed that the inhibitors of JNK and PI3K/Akt inhibited the establishment of persistence, but those of MAPK/ERK kinase (MEK; as an inhibitor for ERK1/2) and p38 MAPK did not. These results indicated that two signaling pathways of JNK and PI3K/Akt were important for the establishment of persistence in Vero E6 cells.

Report on a WHO consultation on immunological endpoints for evaluation of new Japanese encephalitis vaccines, WHO, Geneva, 2-3 September, 2004

The World Health Organization (WHO) is undertaking consultations on immunological responses as parameters for evaluation and licensure of new Japanese encephalitis (JE) vaccines. Immunological markers could be used by vaccine developers and regulatory authorities to assess vaccine efficacy in absence of clinical efficacy data. The consultation which is reported here reviewed current data on mechanisms of protective immunity gathered from animal experimentation, clinical data from licensed vaccines and from vaccine candidates still in clinical development. Immunological assays and readouts for use in evaluation of candidate vaccines were also discussed. The consultation made a series of recommendations for specifications on immunological criteria to assess JE vaccine efficacy. More detailed recommendations will be drafted following further consultations to serve as WHO guidelines for evaluation and licensure for new JE vaccines.

Recombinant nucleocapsid protein-based IgG enzyme-linked immunosorbent assay for the serological diagnosis of SARS

The recombinant nucleocapsid protein (rNP) of severe acute respiratory syndrome (SARS) coronavirus (SARS-CoV) was expressed in a baculovirus system. The purified SARS-CoV rNP was used as an antigen for detection of SARS-CoV antibodies in IgG enzyme-linked immunosorbent assay (ELISA). The ELISA was evaluated in comparison with neutralizing antibody assay and the authentic SARS-CoV antigen-based IgG ELISA. Two-hundred and seventy-six serum samples were collected from health care workers in a hospital in which a nosocomial SARS outbreak took place and used for evaluation. The SARS-CoV rNP-based IgG ELISA has 92% of sensitivity and specificity compared with the neutralizing antibody assay and 94% sensitivity and specificity compared with the authentic SARS-CoV antigen-based IgG ELISA. The results suggest that the newly developed SARS-CoV rNP-based IgG ELISA is a valuable tool for the diagnosis and seroepidemiological study of SARS. The SARS-CoV rNP-based IgG ELISA has an advantage over the conventional IgG ELISA in that the antigen can be prepared by laboratory workers without the risk of infection.

Serological and virological features of dengue fever and dengue haemorrhagic fever in Thailand from 1999 to 2002

Serological and virological features of dengue fever (DF) and dengue haemorrhagic fever (DHF) in Thailand were analysed in 2715 patients from 1999 to 2002. The illness was caused by DEN-1 in 45%, DEN-2 in 32%, DEN-3 in 18% and DEN-4 in 5% of patients. Almost all of the DHF cases caused by DEN-2 and DEN-4 were in secondary infection, while approximately 20% of the DHF cases caused by DEN-1 and DEN-3 were in primary infection. Male:female ratio and age distribution were not different among four serotypes in primary and secondary infections. These results indicate that DEN-1 and DEN-3 induce DHF in both primary and secondary infections, and suggest that DEN-2 and DEN-4 in Thailand are less likely to cause DHF in primary infections.

Review on flavivirus vaccine development. Proceedings of a meeting jointly organised by the World Health Organization and the Thai Ministry of Public Health, 26-27 April 2004, Bangkok, Thailand

In light of the continuous spread of human pathogenic flaviviruses, in particular the mosquito-transmitted species, vaccine development remains a high priority on the public health agenda. On 26-27 April 2004, a conference was held in Bangkok, Thailand, to review current status of flavivirus vaccine development and related issues, focussing on dengue (DEN) and Japanese encephalitis (JE). This event, co-sponsored by the World Health Organization (WHO) and the Thai Ministry of Public Health, reviewed the progress made with vaccine development, sero-epidemiological studies and other accompanying activities critical for vaccine development and vaccination. The considerable interest in and awareness of the flavivirus diseases and their prevention by public health decision makers, as well as the establishment of two dedicated programmes for dengue and Japanese encephalitis vaccine development raise hopes that new or improved vaccines will become available in the coming years.

Genetic characterization of Yokose virus, a flavivirus isolated from the bat in Japan

Yokose virus (strain Oita-36) was isolated from the bat in Japan in 1971. In the present study, we determined complete nucleotide sequences of Yokose virus using RT-PCR and RACE techniques. Yokose virus genome consists of 10,857 nucleotides in length (accession no. AB114858), containing a single open reading frame (3425 amino acids) encoding 11 viral proteins. We deduced the boundaries of each protein in the polyprotein sequence according to the protein cleavage sites of other flaviviruses. The nucleotide sequences of the 5' and 3' nontranslated region (NTR) and amino acid sequences of individual proteins of the virus were compared with those of six other flaviviruses including Japanese encephalitis virus, dengue-2 virus, yellow fever virus, West Nile virus, tick-borne encephalitis virus, and Rio Bravo virus or Modoc virus. Yokose virus demonstrated the highest similarity to yellow fever virus. Yokose virus also has CS1 motif, which are well-conserved specifically in mosquito-born flaviviruses, in its 3' NTR. When a part of the NS5 amino acid sequence (345 amino acids) was compared with those of other four flaviviruses, Entebbe bat virus, Sokuluk virus, Sepik virus, and yellow fever virus, the three former viruses are more closely related to Yokose virus than yellow fever virus. Human sera from dengue-virus-infected case and yellow fever vaccine reacted with the viral proteins. Moreover, human serum from a yellow fever vaccine weakly neutralized Yokose virus. Our results suggest that there are cross-reactive antigenicities among Yokose virus and other flaviviruses.

Japanese encephalitis virus in meningitis patients, Japan

Cerebrospinal fluid specimens from 57 patients diagnosed with meningitis were tested for Japanese encephalitis virus. Total RNA was extracted from the specimens and amplified. Two products had highest homology with Nakayama strain and 2 with Ishikawa strain. Results suggest that Japanese encephalitis virus causes some aseptic meningitis in Japan.

Immunological detection of severe acute respiratory syndrome coronavirus by monoclonal antibodies

In order to establish immunological detection methods for severe acute respiratory syndrome coronavirus (SARS-CoV), we established monoclonal antibodies directed against structural components of the virus. B cell hybridomas were generated from mice that were hyper-immunized with inactivated SARS-CoV virion. By screening 2,880 generated hybridomas, we established three hybridoma clones that secreted antibodies specific for nucleocapsid protein (N) and 27 clones that secreted antibodies specific for spike protein (S). Among these, four S-protein specific antibodies had in vitro neutralization activity against SARS-CoV infection. These monoclonal antibodies enabled the immunological detection of SARS-CoV by immunofluorescence staining, Western blot or immunohistology. Furthermore, a combination of monoclonal antibodies with different specificities allowed the establishment of a highly sensitive antigen-capture sandwich ELISA system. These monoclonal antibodies would be a useful tool for rapid and specific diagnosis of SARS and also for possible antibody-based treatment of the disease.

Genotypic characterization of the DNA polymerase and sensitivity to antiviral compounds of foscarnet-resistant herpes simplex virus type 1 (HSV-1) derived from a foscarnet-sensitive HSV-1 strain

Foscarnet is widely used for the treatment of acyclovir-resistant herpesvirus infections, and foscarnet-resistant herpesvirus infections are a serious concern in immunocompromised patients. Twenty-seven single-plaque isolates of herpes simplex virus type 1 (HSV-1) resistant to foscarnet were selected from foscarnet- and acyclovir-sensitive HSV-1 strain TAS by exposure to foscarnet, and the DNA polymerase genes were analyzed. The sensitivities of these mutants to foscarnet, cidofovir, S2242, acyclovir, ganciclovir, and penciclovir were determined. A single amino acid substitution, double amino acid substitutions, and a combination of a single amino acid substitution with a deletion or insertion of amino acid residues in the viral DNA polymerase were demonstrated in 21, 4, and 2 isolates, respectively. Of the 27 isolates, an amino acid substitution of serine for asparagine at amino acid position 724 in the DNA polymerase (724 S-N) was detected in 8 isolates. An amino acid substitution in conserved region II was demonstrated in these eight isolates as well as four other isolates. The mutation in the DNA polymerase responsible for resistance to foscarnet was located between the pre-IV region and conserved region V, especially within conserved region II. All the isolates were sensitive or hypersensitive to cidofovir and ganciclovir. Seven, 5, and 15 of the 27 isolates were also sensitive to S2242, acyclovir, and penciclovir, respectively. Thus, most of the foscarnet-resistant HSV-1 isolates were sensitive or hypersensitive to cidofovir and ganciclovir.

Tyrosine dephosphorylation of STAT3 in SARS coronavirus-infected Vero E6 cells

Severe acute respiratory syndrome (SARS) has become a global public health emergency. p38 mitogen‐activated protein kinase (MAPK) and its downstream targets are activated in SARS coronavirus (SARS‐CoV)‐infected Vero E6 cells and activation of p38 MAPK enhances the cytopathic effects of SARS‐CoV infection. In addition, weak activation of Akt cannot prevent SARS‐CoV infection‐induced apoptosis in Vero E6 cells. In the present study, we demonstrated that signal transducer and activator of transcription (STAT) 3, which is constitutively phosphorylated at tyrosine (Tyr)‐705 and slightly phosphorylated at serine (Ser)‐727 in Vero E6 cells, was dephosphorylated at Tyr‐705 on SARS‐CoV infection. In addition to phosphorylation of p38 MAPK in virus‐infected cells, other MAPKs, i.e., extracellular signal‐regulated kinase (ERK) 1/2 and c‐Jun N‐terminal kinase (JNK), were phosphorylated. Although inhibitors of ERK1/2 and JNK (PD98059 and SP600125) had no effect on phosphorylation status of STAT3, inhibitors of p38 MAPK (SB203580 and SB202190) partially inhibited dephosphorylation of STAT3 at Tyr‐705. Tyr‐705‐phosphorylated STAT3 was localized mainly in the nucleus in mock infected cells, whereas STAT3 disappeared from the nucleus in virus‐infected cells. As STAT3 acts as an activator of transcription in the nucleus, these results suggest that STAT3 lacks its activity on transcription in SARS‐CoV‐infected Vero E6 cells.

Inhibitory effect of mizoribine and ribavirin on the replication of severe acute respiratory syndrome (SARS)-associated coronavirus

The activity of inosine-5′-monophosphate dehydrogenase (IMPDH) inhibitors, mizoribine and ribavirin, against severe acute respiratory syndrome (SARS)-associated coronavirus (SARS-CoV) was determined by plaque reduction and yield reduction assays. Mizoribine and ribavirin selectively inhibited replication of SARS-CoV. The 50% inhibitory concentration (IC₅₀) of mizoribine for SARS-CoV Frankfurt-1 and SARS-CoV HKU39849, as determined by plaque reduction was 3.5 μg/ml and 16 μg/ml, respectively, and the IC₅₀ of ribavirin for SARS-CoV Frankfurt-1 and SARS-CoV HKU39849 was 20 μg/ml and 80 μg/ml, while the 50% cytotoxic concentration of mizoribine and ribavirin for Vero E6 cells exceeded 200 μg/ml. In a yield reduction assay, mizoribine (10 μg/ml) and ribavirin (40 μg/ml) inhibited the replication of SARS-CoV and reduced the infectious SARS-CoV titers to one-tenth or less. Mizoribine inhibited replication of SARS-CoV more strongly than ribavirin. However, neither drug could completely inhibit replication of SARS-CoV even at concentrations up to 100 μg/ml.

Development and evaluation of fluorogenic TaqMan reverse transcriptase PCR assays for detection of dengue virus types 1 to 4

The fluorogenic TaqMan reverse transcriptase PCR (RT-PCR) assay was developed for detecting each of the dengue virus (DV) types 1 to 4. DV genome was detected in all the 35 serum samples from confirmed dengue cases by the TaqMan RT-PCR, although it was not detected in 13 and 21% by conventional type-specific and cross-reactive RT-PCR, respectively.

Recombinant nucleoprotein-based serological diagnosis of Crimean-Congo hemorrhagic fever virus infections

An enzyme-linked immunosorbent assay (ELISA) using recombinant nucleoprotein (rNP) was reported for the detection of immunoglobulin G (IgG) antibodies to Crimean-Congo hemorrhagic fever (CCHF) virus (CCHFV). The immunoglobulin M (IgM)-capture ELISA was developed for the diagnosis of CCHFV infections, using CCHFV rNP as an antigen. These newly developed assays were applied to a study of a CCHF-outbreak and evaluated with sera collected from patients diagnosed as having CCHF by positive reverse transcription-polymerase chain reaction (RT-PCR) and by detection of IgG response. IgM antibodies to CCHFV were detected in 10 of the 13 patients. IgM antibodies to the rNP of CCHFV were detected by the CCHFV rNP-based IgM-capture ELISA in all 6 patients in whom IgG responses were demonstrated, while it was not detected in the 10 patients in whom IgG responses were not demonstrated. Furthermore, the IgM antibodies were detected in 6 of the 61 residents living a CCHF endemic area during the endemic season, while it was not detected in any of the 48 Japanese residents that had never visited the CCHF endemic area. It is concluded that this newly developed CCHFV rNP-based IgM-capture ELISA is a useful method for the diagnosis of CCHFV infections.