Development of a semi-quantitative real-time RT-PCR for the detection of measles virus

Identification of a measles variant displaying mutations impacting molecular diagnostics, Geneva, Switzerland, 2023

Real-time PCR is one of the most widely used techniques to diagnose measles cases. Here we report measles virus variants with three genetic mutations in the reverse primer annealing site of a widely used PCR. The mutations result in a slight loss of the PCR sensitivity. Variants bearing the three mutations presently circulate in different countries since at least the end of 2021. Our findings highlight the usefulness of molecular surveillance in monitoring if oligonucleotides in diagnostic tests remain adequate.

Simultaneous Detection and Differentiation between Wild-Type and Vaccine Measles Viruses by a Multiplex Real-Time Reverse Transcription-PCR Assay

Measles is one of the most contagious viral respiratory infections and was declared to be eliminated from Canada in 1998; however, measles cases and outbreaks still occur every year through reintroduction from other parts of the world. Laboratory confirmation of measles virus (MV) RNA by real-time PCR provides a definitive diagnosis, and molecular analysis to determine the genotype is the only way to distinguish between wild-type and vaccine strains. This distinction is important since live attenuated vaccine strains are able to replicate in the patient and can be associated with rash and fever but are poorly transmissible, if at all. Prompt reporting of measles cases to local authorities, including differentiation between wild-type and vaccine strains, allows for optimal management and contact tracing. The development and validation of a multiplex real-time reverse transcription-PCR (rtRT-PCR) assay for the simultaneous detection and differentiation of the Moraten and Schwarz vaccine strains from presumptive wild-type MV in a format that can be easily implemented for high-throughput testing of patient samples are reported here. This assay is sensitive, specific, reproducible, and 100% accurate in comparison with the gold standard comparator assay.

Multimodal safety assessment of measles-mumps-rubella vaccination after pediatric liver transplantation

Live-attenuated vaccines are currently contraindicated in solid-organ transplant recipients. However, the risk of vaccine-preventable infections is lifelong, and can be particularly severe after transplantation. In this prospective interventional national cohort study, 44 pediatric liver transplant recipients with measles IgG antibodies <150 IU/L (below seroprotection threshold) received measles-mumps-rubella vaccine (MMR) at a median of 6.3 years posttransplantation (interquartile range, 4.0 to 10.9). A maximum of two additional doses were administered in nonresponders or when seroprotection was lost. Vaccine responses occurred in 98% (95% confidence interval [CI], 88-100) of patients. Seroprotection at 1-, 2-, and 3-year follow-up reached 62% (95% CI, 45-78), 86% (95% CI, 70-95), and 89% (95% CI, 67-99), respectively. All patients responded appropriately to the booster dose(s). Vaccinations were well tolerated and no serious adverse event attributable to vaccination was identified during the 8-week follow-up period (or later), using a multimodal approach including standardized telephone interviews, diarized side effect reporting, and monitoring of vaccinal virus shedding. We conclude that live attenuated MMR vaccine can be administered in liver transplant recipients fulfilling specific eligibility criteria (>1 year posttransplantation, low immunosuppression, lymphocyte count ≥0.75 G/L), inducing seroprotection in most subjects. (Clinicaltrials.gov number NCT01770119).

Phylogenetic and epidemiological analysis of measles outbreaks in Denmark, 2013 to 2014

Despite the introduction of safe, effective vaccines decades ago and joint global public health efforts to eliminate measles, this vaccine-preventable disease continues to pose threats to children’s health worldwide. During 2013 and 2014, measles virus was introduced into Denmark through several independent importations. This resulted in a number of secondary cases (n = 7), with two clusters in 2013 and one in 2014. In total, there were 44 cases of measles. Most cases (n = 41) were laboratory confirmed by detection of measles virus genome by real-time reverse transcription (RT)-PCR and IgM antibodies. The viruses from confirmed cases were genotyped by sequencing. Only one genotype circulated each year, i.e. D8 and B3, respectively. Sequencing of measles virus from different clinical specimens from the same patients revealed that sequence variants of measles viruses might co-exist and co-transmit during an outbreak. The majority of the cases were unvaccinated (n = 27) or recipients of one dose of measles-mumps-rubella (MMR) vaccine (n = 7). In addition, two fully vaccinated adult cases were reported in 2014. We demonstrate the transmission of measles virus in a population in which the two-dose MMR vaccination coverage rate was 80% and how even vaccinated individuals may be at risk of contracting measles once transmission has been established.

Improving statistical inference on pathogen densities estimated by quantitative molecular methods: malaria gametocytaemia as a case study

Background

Quantitative molecular methods (QMMs) such as quantitative real-time polymerase chain reaction (q-PCR), reverse-transcriptase PCR (qRT-PCR) and quantitative nucleic acid sequence-based amplification (QT-NASBA) are increasingly used to estimate pathogen density in a variety of clinical and epidemiological contexts. These methods are often classified as semi-quantitative, yet estimates of reliability or sensitivity are seldom reported. Here, a statistical framework is developed for assessing the reliability (uncertainty) of pathogen densities estimated using QMMs and the associated diagnostic sensitivity. The method is illustrated with quantification of Plasmodium falciparum gametocytaemia by QT-NASBA.

Results

The reliability of pathogen (e.g. gametocyte) densities, and the accompanying diagnostic sensitivity, estimated by two contrasting statistical calibration techniques, are compared; a traditional method and a mixed model Bayesian approach. The latter accounts for statistical dependence of QMM assays run under identical laboratory protocols and permits structural modelling of experimental measurements, allowing precision to vary with pathogen density. Traditional calibration cannot account for inter-assay variability arising from imperfect QMMs and generates estimates of pathogen density that have poor reliability, are variable among assays and inaccurately reflect diagnostic sensitivity. The Bayesian mixed model approach assimilates information from replica QMM assays, improving reliability and inter-assay homogeneity, providing an accurate appraisal of quantitative and diagnostic performance.

Conclusions

Bayesian mixed model statistical calibration supersedes traditional techniques in the context of QMM-derived estimates of pathogen density, offering the potential to improve substantially the depth and quality of clinical and epidemiological inference for a wide variety of pathogens.

Electronic supplementary material

The online version of this article (doi:10.1186/s12859-014-0402-2) contains supplementary material, which is available to authorized users.

Live-attenuated measles virus vaccine targets dendritic cells and macrophages in muscle of nonhuman primates

Although live-attenuated measles virus (MV) vaccines have been used successfully for over 50 years, the target cells that sustain virus replication in vivo are still unknown. We generated a reverse genetics system for the live-attenuated MV vaccine strain Edmonston-Zagreb (EZ), allowing recovery of recombinant (r)MV(EZ). Three recombinant viruses were generated that contained the open reading frame encoding enhanced green fluorescent protein (EGFP) within an additional transcriptional unit (ATU) at various positions within the genome. rMV(EZ)EGFP(1), rMV(EZ)EGFP(3), and rMV(EZ)EGFP(6) contained the ATU upstream of the N gene, following the P gene, and following the H gene, respectively. The viruses were compared in vitro by growth curves, which indicated that rMV(EZ)EGFP(1) was overattenuated. Intratracheal infection of cynomolgus macaques with these recombinant viruses revealed differences in immunogenicity. rMV(EZ)EGFP(1) and rMV(EZ)EGFP(6) did not induce satisfactory serum antibody responses, whereas both in vitro and in vivo rMV(EZ)EGFP(3) was functionally equivalent to the commercial MV(EZ)-containing vaccine. Intramuscular vaccination of macaques with rMV(EZ)EGFP(3) resulted in the identification of EGFP(+) cells in the muscle at days 3, 5, and 7 postvaccination. Phenotypic characterization of these cells demonstrated that muscle cells were not infected and that dendritic cells and macrophages were the predominant target cells of live-attenuated MV.

IMPORTANCE

Even though MV strain Edmonston-Zagreb has long been used as a live-attenuated vaccine (LAV) to protect against measles, nothing is known about the primary cells in which the virus replicates in vivo. This is vital information given the push to move toward needle-free routes of vaccination, since vaccine virus replication is essential for vaccination efficacy. We have generated a number of recombinant MV strains expressing enhanced green fluorescent protein. The virus that best mimicked the nonrecombinant vaccine virus was formulated according to protocols for production of commercial vaccine virus batches, and was subsequently used to assess viral tropism in nonhuman primates. The virus primarily replicated in professional antigen-presenting cells, which may explain why this LAV is so immunogenic and efficacious.

Acute measles encephalitis in partially vaccinated adults

BACKGROUND

The pathogenesis of acute measles encephalitis (AME) is poorly understood. Treatment with immune-modulators is based on theories that post-infectious autoimmune responses cause demyelination. The clinical course and immunological parameters of AME were examined during an outbreak in Vietnam.

METHODS AND FINDINGS

Fifteen measles IgM-positive patients with confusion or Glasgow Coma Scale (GCS) score below 13, and thirteen with uncomplicated measles were enrolled from 2008-2010. Standardized clinical exams were performed and blood collected for lymphocyte and measles- and auto-antibody analysis. The median age of AME patients was 21 years, similar to controls. Eleven reported receiving measles vaccination when aged one year. Confusion developed a median of 4 days after rash. Six patients had GCS <8 and four required mechanical ventilation. CSF showed pleocytosis (64%) and proteinorrhachia (71%) but measles virus RNA was not detected. MRI revealed bilateral lesions in the cerebellum and brain stem in some patients. Most received dexamethasone +/- IVIG within 4 days of admission but symptoms persisted for ≥3 weeks in five. The concentration of voltage gated calcium channel-complex-reactive antibodies was 900 pM in one patient, and declined to 609 pM ∼ 3 months later. Measles-reactive IgG antibody avidity was high in AME patients born after vaccine coverage exceeded 50% (∼ 25 years earlier). AME patients had low CD4 (218/µl, p = 0.029) and CD8 (200/µl, p = 0.012) T-cell counts compared to controls.

CONCLUSION

Young adults presenting with AME in Vietnam reported a history of one prior measles immunization, and those aged <25 years had high measles-reactive IgG avidity indicative of prior vaccination. This suggests that one-dose measles immunization is not sufficient to prevent AME in young adults and reinforces the importance of maintaining high coverage with a two-dose measles immunization schedule. Treatment with corticosteroids and IVIG is common practice, and should be assessed in randomized clinical trials.

A rapid and sensitive one step-SYBR green based semi quantitative real time RT-PCR for the detection of peste des petits ruminants virus in the clinical samples

A sensitive and rapid single step real time (rt) RT-PCR was standardized using one-step Brilliant SYBR Green kit® for detection and semi-quantitation of peste des petitis ruminants virus (PPRV) using the virus RNA and matrix (M) protein gene-specific primers and compared with established conventional RT-PCR and TaqMan RT-PCR. The assay amplifies a 124 bp fragment of the PPRV M gene with T(m) of 78.28 to 78.50. The assay was linear within a range of 50 ng to 0.5 fg total virus RNA with a detection limit (sensitivity) of 0.5 fg. Based on the serial dilution of the live-attenuated PPR vaccine virus, the detection limit was ~0.0001 cell culture infectious dose 50% units (TCID(50)). Additionally, swab materials spiked with known titre of vaccine virus were equally well detected in the assay. The standardized rt RT-PCR was easily employed for the detection of PPRV nucleic acid directly in the field and experimental clinical samples. The assay detected the PPRV nucleic acid as early as 3 day post infection (dpi) and up to 20 dpi in swab materials from the experimental samples. The assay was rapid and more sensitive than TaqMan and conventional RT-PCR in the detection of PPRV nucleic acid from the PPR suspected clinical samples of sheep and goats. Therefore, the established, simplified SYBR green rt RT-PCR is an alternative test to the already existing various diagnostic assays and could be useful for rapid clinical diagnosis with advantage in reducing risk of contamination.

Biological feasibility of measles eradication

Because of the success of global measles control programs, the World Health Organization (WHO), along with its partner agencies, is once again considering the possibility of setting a target date for measles eradication. Measles would be the fourth viral agent to be eradicated joining the successful programs to eradicate smallpox and rinderpest virus, and the continuing effort to eradicate polio virus. A description of the recent progress toward measles eradication was recently published as a supplement in the Journal of Infectious Diseases (15 July, 2011, 204 (Suppl. 1)) and the reader is referred to this document for a detailed summary of the global status of measles control. This review will focus on the biologic and virologic aspects of measles eradication.

Early target cells of measles virus after aerosol infection of non-human primates

Measles virus (MV) is highly infectious, and has long been thought to enter the host by infecting epithelial cells of the respiratory tract. However, epithelial cells do not express signaling lymphocyte activation molecule (CD150), which is the high-affinity cellular receptor for wild-type MV strains. We have generated a new recombinant MV strain expressing enhanced green fluorescent protein (EGFP), based on a wild-type genotype B3 virus isolate from Khartoum, Sudan (KS). Cynomolgus macaques were infected with a high dose of rMV^KSEGFP by aerosol inhalation to ensure that the virus could reach the full range of potential target cells throughout the entire respiratory tract. Animals were euthanized 2, 3, 4 or 5 days post-infection (d.p.i., n = 3 per time point) and infected (EGFP⁺) cells were identified at all four time points, albeit at low levels 2 and 3 d.p.i. At these earliest time points, MV-infected cells were exclusively detected in the lungs by fluorescence microscopy, histopathology and/or virus isolation from broncho-alveolar lavage cells. On 2 d.p.i., EGFP⁺ cells were phenotypically typed as large mononuclear cells present in the alveolar lumen or lining the alveolar epithelium. One to two days later, larger clusters of MV-infected cells were detected in bronchus-associated lymphoid tissue (BALT) and in the tracheo-bronchial lymph nodes. From 4 d.p.i. onward, MV-infected cells were detected in peripheral blood and various lymphoid tissues. In spite of the possibility for the aerosolized virus to infect cells and lymphoid tissues of the upper respiratory tract, MV-infected cells were not detected in either the tonsils or the adenoids until after onset of viremia. These data strongly suggest that in our model MV entered the host at the alveolar level by infecting macrophages or dendritic cells, which traffic the virus to BALT or regional lymph nodes, resulting in local amplification and subsequent systemic dissemination by viremia.

Measles remains an important vaccine-preventable cause of morbidity and mortality in developing countries. The causative agent, measles virus (MV), is one of the most contagious viruses known. Measles has an incubation time of approximately two weeks, and surprisingly little is known about the early events after MV infection. Epithelial cells in the upper respiratory tract have long been considered as early target cells, but more recently alveolar macrophages (AM) and dendritic cells (DC) have been proposed as alternatives. We have infected cynomolgus macaques with a high dose of a recombinant EGFP-expressing MV strain via aerosol inhalation, to ensure that the virus had access to the entire respiratory tract. At 2 days post-infection, MV-infected mononuclear cells were detectable in the alveolar lumen but not in the upper respiratory tract. These infected cells migrated through the bronchus-associated lymphoid tissue to the draining tracheo-bronchial lymph node at 3 days post-infection. Systemic infection was initiated from this point, as observed in macaques euthanized 4 or 5 days post-infection. Thus, even though the aerosolized virus had access to epithelial cells and lymphoid tissues along the entire respiratory tract, AM and DC in the lungs were the first cells that sustained MV replication.

Application of semi-quantitative M gene-based hydrolysis probe (TaqMan) real-time RT-PCR assay for the detection of peste des petits ruminants virus in the clinical samples for investigation into clinical prevalence of disease

Peste des petits ruminants (PPR) is a contagious, notifiable and economically important transboundary viral disease of small ruminants. In this study, a hydrolysis probe-based real-time reverse transcription-polymerase chain reaction (rt RT-PCR) assay for the detection and semi-quantification of PPR virus (PPRV) nucleic acid was developed using the virus RNA and matrix (M) gene-specific primers with Hex-labelled fluorescent probe and applied for the detection of PPRV in clinical samples to identify outbreaks and to monitor the prevalence of disease. The assay was found specific with a sensitivity detection limit of 0.5 pg of total PPRV RNA. Based on a serial dilution of the live-attenuated PPR vaccine virus, the detection limits were approximately 0.1 and 1 TCID₅₀ for the hydrolysis probe and conventional RT-PCR assays, respectively. The assay was linear within a range of 50 ng to 0.5 pg total virus RNA with an intra-assay coefficient of variation (CV) in the range of 0.91-2.86% and an inter-assay CV ranging between 0.59% and 2.37%. The standardized rt RT-PCR was easily employed for the detection of PPRV nucleic acid directly in the experimental/field clinical samples. This assay detected the PPRV in pre-clinical swab materials as early as the 4th day post-infection (dpi) and up to 17th dpi in nasal, ocular and oral swabs collected from experimentally infected animals. The rt RT-PCR was rapid, specific and 10 times more sensitive than conventional RT-PCR. It is an alternative test to the existing diagnostic assays and could be useful with enhanced applicability in field clinical diagnosis by avoiding the use of expensive commercial real-time PCR reagents. This assay was adopted directly in the detection of PPRV nucleic acid in clinical samples collected from sheep and goats suspected of PPR to monitor outbreak situations and the clinical prevalence of PPR in India.

Detection of measles virus RNA on SYBR green real-time reverse transcription-polymerase chain reaction

BACKGROUND

As the coverage rate of the measles vaccine increases, not all patients present the typical symptoms of measles after exposure to the measles virus (MV). The virus loads in clinical specimens from patients with vaccine-modified non-typical measles are expected to be low compared with those of primary MV infection. A rapid and sensitive laboratory procedure is required for diagnosis of measles.

METHODS

SYBR Green (TaKaRa) and TaqMan (ABI) real-time reverse transcription-polymerase chain reaction (RT-PCR) assays were developed to detect MV-RNA. For the real-time RT-PCR, primer sets were designed from a region of the MV H gene of the Edmonston strain (genotype A). A TaqMan probe specific for the H gene of genotype D MV was used. The minimum detectable level of MV-RNA in the SYBR Green and TaqMan real-time RT-PCR assays was evaluated using synthetic MV-RNA. The sensitivity of real-time RT-PCR was compared with that of nested RT-PCR and the virus isolation method using throat swabs and peripheral blood samples from patients with measles.

RESULTS

The minimum detectable level of RNA was 10 and 10(2) copies for SYBR Green RT-PCR and TaqMan RT-PCR, respectively. Ten-10(6) copies of standard RNA were linearly detected on SYBR Green RT-PCR. The sensitivity of SYBR Green RT-PCR was equal to that of nested RT-PCR. MV-RNA was detected in virus isolation-negative throat swabs on SYBR Green RT-PCR.

CONCLUSION

SYBR Green RT-PCR is a highly sensitive, rapid, and useful diagnostic procedure for the detection of MV.

In vivo tropism of attenuated and pathogenic measles virus expressing green fluorescent protein in macaques

The global increase in measles vaccination has resulted in a significant reduction of measles mortality. The standard route of administration for the live-attenuated measles virus (MV) vaccine is subcutaneous injection, although alternative needle-free routes, including aerosol delivery, are under investigation. In vitro, attenuated MV has a much wider tropism than clinical isolates, as it can use both CD46 and CD150 as cellular receptors. To compare the in vivo tropism of attenuated and pathogenic MV, we infected cynomolgus macaques with pathogenic or attenuated recombinant MV expressing enhanced green fluorescent protein (GFP) (strains IC323 and Edmonston, respectively) via the intratracheal or aerosol route. Surprisingly, viral loads and cellular tropism in the lungs were similar for the two viruses regardless of the route of administration, and CD11c-positive cells were identified as the major target population. However, only the pathogenic MV caused significant viremia, which resulted in massive virus replication in B and T lymphocytes in lymphoid tissues and viral dissemination to the skin and the submucosa of respiratory epithelia. Attenuated MV was rarely detected in lymphoid tissues, and when it was, only in isolated infected cells. Following aerosol inhalation, attenuated MV was detected at early time points in the upper respiratory tract, suggesting local virus replication. This contrasts with pathogenic MV, which invaded the upper respiratory tract only after the onset of viremia. This study shows that despite in vitro differences, attenuated and pathogenic MV show highly similar in vivo tropism in the lungs. However, systemic spread of attenuated MV is restricted.

Infection of bovine dendritic cells by rinderpest or measles viruses induces different changes in host transcription

The morbilliviruses are a closely related genus which are very similar in their sequences and share a common receptor, but nevertheless show significant restriction in the host species in which they cause disease. One contribution to this restriction might be the nature of the hosts' responses to infection. We have used microarrays to study the changes in the transcriptome of bovine dendritic cells after infection with wild-type (pathogenic) and vaccine (apathogenic) strains of rinderpest virus (RPV), a bovine pathogen, and a wild-type isolate of measles virus (MV), a morbillivirus that causes disease only in humans and some other primates. We found that, as previously observed in human cells, MV induces a rapid interferon response, while that induced by RPV was delayed and much reduced in magnitude. Pathogenic and apathogenic RPV also showed significant differences, with the latter inducing a slightly higher interferon response as well as significant effects on transcription of genes involved in cell cycle regulation.

Measles outbreak linked to a minority group in Austria, 2008

We report on a measles outbreak originating in an anthroposophic community in Austria, 2008. A total of 394 (94·9%) cases fulfilled the outbreak case definition including 168 cases affiliated to the anthroposophic community. The source case was a school pupil from Switzerland. The Austrian outbreak strain was genotype D5, indistinguishable from the Swiss outbreak strain. A school-based retrospective cohort study in the anthroposophic school demonstrated a vaccine effectiveness of 97·3% in pupils who had received a single dose of measles-containing vaccine and 100% in those who had received two doses. The vaccination coverage of the cases in the anthroposophic community was 0·6%. Of the 226 outbreak cases not belonging to the anthroposophic community, the 10–24 years age group was the most affected. Our findings underline the epidemiological significance of suboptimal vaccination coverage in anthroposophic communities and in older age groups of the general population in facilitating measles virus circulation. The findings of this outbreak investigation suggest that the WHO European Region is unlikely to achieve its 2010 target for measles and rubella elimination.

A multiplex TaqMan PCR assay for the detection of measles and rubella virus

Measles and rubella virus cause fever/rash diseases that are difficult to differentiate clinically. Both viruses can be detected in the same clinical specimens and are propagated on the same cell cultures. A single-tube multiplex TaqMan assay is described for the simultaneous and rapid detection of the full spectrum of known genetic variants. The performance of the assay is similar to a conventional nested PCR and generates cDNA with random primers which can be used directly for virus genotyping.

Development and evaluation of a real-time PCR assay for rapid identification and semi-quantitation of measles virus

A real-time PCR assay for measles virus was designed and validated using clinical samples including oral fluids, sera, urines, throat swabs, blood samples, and nasopharyngeal aspirates. The test was specific for measles virus, with a slightly higher sensitivity compared to the conventional nested PCR. Calculation of viral genome number in these samples, by comparison with a standard curve prepared from dilutions of cloned measles virus H gene, indicated that, overall, serum samples tended to have a lower viral load than oral fluid samples, and that the viral load decreased with increasing time after onset of symptoms. The real-time PCR is considered to be a sensitive and specific alternative to the conventional measles PCR, especially in situations where early and rapid diagnosis are important.

Predominant infection of CD150+ lymphocytes and dendritic cells during measles virus infection of macaques

Measles virus (MV) is hypothesized to enter the host by infecting epithelial cells of the respiratory tract, followed by viremia mediated by infected monocytes. However, neither of these cell types express signaling lymphocyte activation molecule (CD150), which has been identified as the receptor for wild-type MV. We have infected rhesus and cynomolgus macaques with a recombinant MV strain expressing enhanced green fluorescent protein (EGFP); thus bringing together the optimal animal model for measles and a virus that can be detected with unprecedented sensitivity. Blood samples and broncho-alveolar lavages were collected every 3 d, and necropsies were performed upon euthanasia 9 or 15 d after infection. EGFP production by MV-infected cells was visualized macroscopically, in both living and sacrificed animals, and microscopically by confocal microscopy and FACS analysis. At the peak of viremia, EGFP fluorescence was detected in skin, respiratory and digestive tract, but most intensely in all lymphoid tissues. B- and T-lymphocytes expressing CD150 were the major target cells for MV infection. Highest percentages (up to 30%) of infected lymphocytes were detected in lymphoid tissues, and the virus preferentially targeted cells with a memory phenotype. Unexpectedly, circulating monocytes did not sustain productive MV infection. In peripheral tissues, large numbers of MV-infected CD11c+ MHC class-II+ myeloid dendritic cells were detected in conjunction with infected T-lymphocytes, suggesting transmission of MV between these cell types. Fluorescent imaging of MV infection in non-human primates demonstrated a crucial role for lymphocytes and dendritic cells in the pathogenesis of measles and measles-associated immunosuppression.

Microplitis demolitor bracovirus genome segments vary in abundance and are individually packaged in virions

Polydnaviruses (PDVs) are distinguished by their unique association with parasitoid wasps and their segmented, double-stranded (ds) DNA genomes that are non-equimolar in abundance. Relatively little is actually known, however, about genome packaging or segment abundance of these viruses. Here, we conducted electron microscopy (EM) and real-time polymerase chain reaction (PCR) studies to characterize packaging and segment abundance of Microplitis demolitor bracovirus (MdBV). Like other PDVs, MdBV replicates in the ovaries of females where virions accumulate to form a suspension called calyx fluid. Wasps then inject a quantity of calyx fluid when ovipositing into hosts. The MdBV genome consists of 15 segments that range from 3.6 (segment A) to 34.3 kb (segment O). EM analysis indicated that MdBV virions contain a single nucleocapsid that encapsidates one circular DNA of variable size. We developed a semi-quantitative real-time PCR assay using SYBR Green I. This assay indicated that five (J, O, H, N and B) segments of the MdBV genome accounted for more than 60% of the viral DNAs in calyx fluid. Estimates of relative segment abundance using our real-time PCR assay were also very similar to DNA size distributions determined from micrographs. Analysis of parasitized Pseudoplusia includens larvae indicated that copy number of MdBV segments C, B and J varied between hosts but their relative abundance within a host was virtually identical to their abundance in calyx fluid. Among-tissue assays indicated that each viral segment was most abundant in hemocytes and least abundant in salivary glands. However, the relative abundance of each segment to one another was similar in all tissues. We also found no clear relationship between MdBV segment and transcript abundance in hemocytes and fat body.

Measles vaccination of macaques by dry powder inhalation

Measles vaccination via the aerosol route has proven effective under field conditions, using vaccine reconstituted prior to nebulization. Inhalation of a dry powder aerosol vaccine would have additional benefits, including easier logistics of administration, reduced cold chain dependence and the potential of single dose administration. We have evaluated two candidate dry powder measles vaccine formulations in macaques. Specific immune responses were demonstrated, but levels of immunity were lower than in animals vaccinated by injection or by nebulized aerosol. These studies provide proof of principle that dry powder inhalation is a possible route for measles vaccination, but suggest that either the vaccine formulation or the method of delivery need to be improved for a better immune response.

Aerosol measles vaccination in macaques: preclinical studies of immune responses and safety

The comparative efficacy and safety of measles vaccination via the aerosol route versus subcutaneous injection has not been fully resolved. We vaccinated cynomolgus monkeys (Macaca fascicularis) with the live-attenuated Edmonston-Zagreb measles virus (MV) vaccine and compared different routes of administration in the immunocompetent and the immunocompromised host. Immunogenicity and protective efficacy of aerosol vaccination using devices similar to those previously used in humans were comparable to those in animals vaccinated by injection. No evidence for a safety hazard associated with the route of vaccination was detected. The results of this study support further clinical evaluation of aerosol vaccination for measles.

Detection and monitoring of virus infections by real-time PCR

The employment of polymerase chain reaction (PCR) techniques for virus detection and quantification offers the advantages of high sensitivity and reproducibility, combined with an extremely broad dynamic range. A number of qualitative and quantitative PCR virus assays have been described, but commercial PCR kits are available for quantitative analysis of a limited number of clinically important viruses only. In addition to permitting the assessment of viral load at a given time point, quantitative PCR tests offer the possibility of determining the dynamics of virus proliferation, monitoring of the response to treatment and, in viruses displaying persistence in defined cell types, distinction between latent and active infection. Moreover, from a technical point of view, the employment of sequential quantitative PCR assays in virus monitoring helps identifying false positive results caused by inadvertent contamination of samples with traces of viral nucleic acids or PCR products. In this review, we provide a survey of the current state-of-the-art in the application of the real-time PCR technology to virus analysis. Advantages and limitations of the RQ-PCR methodology, and quality control issues related to standardization and validation of diagnostic assays are discussed.

Development of quantitative gene-specific real-time RT-PCR assays for the detection of measles virus in clinical specimens

Real-time RT-PCR assays targeting sequences in the measles virus (MV) nucleoprotein (N), fusion (F), and hemagglutinin (H) genes were developed for the detection of MV RNA in clinical specimens. Four primer and probe sets each for the N, F, and H genes were evaluated and reaction conditions optimized. Using dilution series of synthetic RNAs, the limits of detection were determined to be approximately 10 copies for each target RNA/reaction. The relationship between C(t) values and RNA concentration was linear within a range of 10-10(6) RNA copies/reaction, and intra- and inter-assay variability was low. The N gene-specific real-time assay detected MV RNA in 100% of clinical samples from confirmed measles cases compared to 41% by standard RT-PCR. The MV H and F gene-specific real-time assays detected MV RNA in 93% and 82% of these specimens, respectively. Real-time assays could detect RNA from strains representing each active genotype of MV and were also highly specific, as no false positives were identified when samples known to contain other respiratory viruses were tested. Real-time RT-PCR assays will be available to support routine measles laboratory surveillance, to facilitate research projects on pathogenesis that require sensitive and quantitative detection of MV RNA, and to aid in the investigation of serious disease sequelae resulting from natural measles infection or vaccination with measles-containing vaccines.

Rapid detection and quantitation of viral hemorrhagic septicemia virus in experimentally challenged rainbow trout by real-time RT-PCR

A quantitative real-time RT-PCR (Q-RT-PCR) was developed to detect and determine the amount of viral hemorrhagic septicemia virus (VHSV) in organs of experimentally infected rainbow trout. Primers and TaqMan probes targeting the glycoprotein (G) and the nucleoprotein (N) genes of the virus were designed. The efficiency, linear range and detection limit of the Q-RT-PCR were assessed on cell cultured virus samples. VHSV N gene amplification was more efficient and more sensitive than the VHSV G amplicon. On cell culture grown virus, samples could be accurately assayed over a range of seven logs of infectious particles per reaction. To demonstrate the utility of Q-RT-PCR in vivo, bath infection trials were carried out and samples from fish spleen, kidney, liver and blood were harvested and tested for VHSV. Q-RT-PCR was a more reliable method than either conventional RT-PCR or the cell culture assay for virus diagnosis. Results of VHSV RNA detection in fish shortly after infection as well as on asymptomatic fish several weeks after experimental challenge are presented here. This is the first report showing the utility of Q-RT-PCR for VHSV detection and quantitation both in vitro and in vivo. The suitability of this method to test the efficacy of antiviral treatments is also discussed.