Kalanthe Horiuchi

Infection and transmission of Rift Valley fever viruses lacking the NSs and/or NSm genes in mosquitoes: potential role for NSm in mosquito infection.

Background Rift Valley fever virus is an arthropod-borne human and animal pathogen responsible for large outbreaks of acute and febrile illness throughout Africa and the Arabian Peninsula. Reverse genetics technology has been used to develop deletion mutants of the virus that lack the NSs and/or NSm virulence genes and have been shown to be stable, immunogenic and protective against Rift Valley fever virus infection in animals. We assessed the potential for these deletion mutant viruses to infect and be transmitted by Aedes mosquitoes, which are the principal vectors for maintenance of the virus in nature and emergence of virus initiating disease outbreaks, and by Culex mosquitoes which are important amplification vectors. Methodology and Principal Findings Aedes aegypti and Culex quinquefasciatus mosquitoes were fed bloodmeals containing the deletion mutant viruses. Two weeks post-exposure mosquitoes were assayed for infection, dissemination, and transmission. In Ae. aegypti, infection and transmission rates of the NSs deletion virus were similar to wild type virus while dissemination rates were significantly reduced. Infection and dissemination rates for the NSm deletion virus were lower compared to wild type. Virus lacking both NSs and NSm failed to infect Ae. aegypti. In Cx. quinquefasciatus, infection rates for viruses lacking NSm or both NSs and NSm were lower than for wild type virus. Conclusions/Significance In both species, deletion of NSm or both NSs and NSm reduced the infection and transmission potential of the virus. Deletion of both NSs and NSm resulted in the highest level of attenuation of virus replication. Deletion of NSm alone was sufficient to nearly abolish infection in Aedes aegypti mosquitoes, indicating an important role for this protein. The double deleted viruses represent an ideal vaccine profile in terms of environmental containment due to lack of ability to efficiently infect and be transmitted by mosquitoes.

Culex Flavivirus and West Nile Virus in Culex quinquefasciatus Populations in the Southeastern United States

ABSTRACT Little is known of the interactions between insect-only flaviviruses and other arboviruses in their mosquito hosts, or the potential public health significance of these associations. The specific aims of this study were to describe the geographic distribution, prevalence, and seasonal infection rates of Culex flavivirus (CxFV) and West Nile virus (WNV) in Culex quinquefasciatus Say in the Southeastern United States, investigate the potential association between CxFV and WNV prevalence in Cx. quinquefasciatus and describe the phylogenetic relationship among CxFV and WNV isolates from the Southeastern United States and around the world. Using ArboNET records, 11 locations were selected across Georgia, Mississippi, and Louisiana that represented a range of WNV human case incidence levels. Cx. quinquefasciatus were trapped weekly throughout the summer of 2009 and pools were screened for flavivirus RNA by reverse transcriptase polymerase chain reaction. Cx. quinquefasciatus from Georgia had significantly higher CxFV infection rates than either Mississippi or Louisiana. CxFV was not detected in Mississippi after July, and no CxFV was detected in Cx. quinquefasciatus in Louisiana. In Georgia, CxFV infection rates were variable between and within counties and over time. WNV infection rates were not significantly different across states or months, and WNV sequences from all three states were identical to each other in the envelope and NS5 gene regions. Phylogenetically, NS5 and E gene sequences from Georgia CxFV isolates clustered with CxFV from Japan, Iowa, and Texas. Multiple CxFV genetic variants were found circulating simultaneously in Georgia. No evidence was found supporting an association between WNV and CxFV infection prevalence in Cx. quinquefasciatus.

Deletion of the NSm Virulence Gene of Rift Valley Fever Virus Inhibits Virus Replication in and Dissemination from the Midgut of Aedes aegypti Mosquitoes

Background Previously, we investigated the role of the Rift Valley fever virus (RVFV) virulence genes NSs and NSm in mosquitoes and demonstrated that deletion of NSm significantly reduced the infection, dissemination, and transmission rates of RVFV in Aedes aegypti mosquitoes. The specific aim of this study was to further characterize midgut infection and escape barriers of RVFV in Ae. aegypti infected with reverse genetics-generated wild type RVFV (rRVF-wt) or RVFV lacking the NSm virulence gene (rRVF-ΔNSm) by examining sagittal sections of infected mosquitoes for viral antigen at various time points post-infection. Methodology and Principal Findings Ae. aegypti mosquitoes were fed an infectious blood meal containing either rRVF-wt or rRVF-ΔNSm. On days 0, 1, 2, 3, 4, 6, 8, 10, 12, and 14 post-infection, mosquitoes from each experimental group were fixed in 4% paraformaldehyde, paraffin-embedded, sectioned, and examined for RVFV antigen by immunofluorescence assay. Remaining mosquitoes at day 14 were assayed for infection, dissemination, and transmission. Disseminated infections were observed in mosquitoes as early as three days post infection for both virus strains. However, infection rates for rRVF-ΔNSm were statistically significantly less than for rRVF-wt. Posterior midgut infections in mosquitoes infected with rRVF-wt were extensive, whereas midgut infections of mosquitoes infected with rRVF-ΔNSm were confined to one or a few small foci. Conclusions/Significance Deletion of NSm resulted in the reduced ability of RVFV to enter, replicate, and disseminate from the midgut epithelial cells. NSm appears to have a functional role in the vector competence of mosquitoes for RVFV at the level of the midgut barrier.

Probable and possible transfusion-transmitted dengue associated with NS1 antigen–negative but RNA confirmed-positive red blood cells

In the absence of active blood donation screening, dengue viruses (DENV) have been implicated in only a limited number of transfusion transmissions worldwide. This study attempted to identify if blood from donors testing negative by an NS1‐antigen (Ag) enzyme‐linked immunosorbent assay (ELISA) but confirmed positive for DENV RNA caused DENV‐related disease in recipients during the epidemic years of 2010 to 2012 in Puerto Rico.

Performance of Dengue Diagnostic Tests in a Single-Specimen Diagnostic Algorithm

BACKGROUND Anti-dengue virus (DENV) immunoglobulin M (IgM) seroconversion has been the reference standard for dengue diagnosis. However, paired specimens are rarely obtained, and the interval for this testing negates its usefulness in guiding clinical case management. The presence of DENV viremia and appearance of IgM during the febrile phase of dengue provides the framework for dengue laboratory diagnosis by using a single serum specimen. METHODS Archived paired serum specimens (n = 1234) from patients with laboratory-confirmed dengue from 2005 through 2011 were used to determine the diagnostic performance of real-time reverse transcription polymerase chain reaction (RT-PCR), for detection of DENV serotypes 1-4, and enzyme-linked immunosorbent assays (ELISAs), for detection of DENV nonstructural protein 1 (NS1) antigen and anti-DENV IgM. RESULTS During 1-3 days after illness onset, real-time RT-PCR and NS1 antigen testing detected 82%-69% and 90%-84% of cases, respectively, as viremia levels declined, while anti-DENV IgM ELISA detected 5%-41% of cases as antibody appeared. Over the 10-day period of the febrile phase of dengue, the cumulative effect of using these 3 types of tests in a diagnostic algorithm confirmed ≥90% of dengue cases. CONCLUSIONS The use of molecular or NS1 antigen tests to detect DENV and one to detect anti-DENV IgM in a single serum specimen collected during the first 10 days of illness accurately identified ≥90% of dengue primary and secondary cases.

Multiplex Microsphere Immunoassays for the Detection of IgM and IgG to Arboviral Diseases

Serodiagnosis of arthropod-borne viruses (arboviruses) at the Division of Vector-Borne Diseases, CDC, employs a combination of individual enzyme-linked immunosorbent assays and microsphere immunoassays (MIAs) to test for IgM and IgG, followed by confirmatory plaque-reduction neutralization tests. Based upon the geographic origin of a sample, it may be tested concurrently for multiple arboviruses, which can be a cumbersome task. The advent of multiplexing represents an opportunity to streamline these types of assays; however, because serologic cross-reactivity of the arboviral antigens often confounds results, it is of interest to employ data analysis methods that address this issue. Here, we constructed 13-virus multiplexed IgM and IgG MIAs that included internal and external controls, based upon the Luminex platform. Results from samples tested using these methods were analyzed using 8 different statistical schemes to identify the best way to classify the data. Geographic batteries were also devised to serve as a more practical diagnostic format, and further samples were tested using the abbreviated multiplexes. Comparative error rates for the classification schemes identified a specific boosting method based on logistic regression “Logitboost” as the classification method of choice. When the data from all samples tested were combined into one set, error rates from the multiplex IgM and IgG MIAs were <5% for all geographic batteries. This work represents both the most comprehensive, validated multiplexing method for arboviruses to date, and also the most systematic attempt to determine the most useful classification method for use with these types of serologic tests.

Clinical and epidemiologic characteristics of dengue and other etiologic agents among patients with acute febrile illness, Puerto Rico, 2012-2015.

Identifying etiologies of acute febrile illnesses (AFI) is challenging due to non-specific presentation and limited availability of diagnostics. Prospective AFI studies provide a methodology to describe the syndrome by age and etiology, findings that can be used to develop case definitions and multiplexed diagnostics to optimize management. We conducted a 3-year prospective AFI study in Puerto Rico. Patients with fever ≤7 days were offered enrollment, and clinical data and specimens were collected at enrollment and upon discharge or follow-up. Blood and oro-nasopharyngeal specimens were tested by RT-PCR and immunodiagnostic methods for infection with dengue viruses (DENV) 1–4, chikungunya virus (CHIKV), influenza A and B viruses (FLU A/B), 12 other respiratory viruses (ORV), enterovirus, Leptospira spp., and Burkholderia pseudomallei. Clinical presentation and laboratory findings of participants infected with DENV were compared to those infected with CHIKV, FLU A/B, and ORV. Clinical predictors of laboratory-positive dengue compared to all other AFI etiologies were determined by age and day post-illness onset (DPO) at presentation. Of 8,996 participants enrolled from May 7, 2012 through May 6, 2015, more than half (54.8%, 4,930) had a pathogen detected. Pathogens most frequently detected were CHIKV (1,635, 18.2%), FLU A/B (1,074, 11.9%), DENV 1–4 (970, 10.8%), and ORV (904, 10.3%). Participants with DENV infection presented later and a higher proportion were hospitalized than those with other diagnoses (46.7% versus 27.3% with ORV, 18.8% with FLU A/B, and 11.2% with CHIKV). Predictors of dengue in participants presenting <3 DPO included leukopenia, thrombocytopenia, headache, eye pain, nausea, and dizziness, while negative predictors were irritability and rhinorrhea. Predictors of dengue in participants presenting 3–5 DPO were leukopenia, thrombocytopenia, facial/neck erythema, nausea, eye pain, signs of poor circulation, and diarrhea; presence of rhinorrhea, cough, and red conjunctiva predicted non-dengue AFI. By enrolling febrile patients at clinical presentation, we identified unbiased predictors of laboratory-positive dengue as compared to other common causes of AFI. These findings can be used to assist in early identification of dengue patients, as well as direct anticipatory guidance and timely initiation of correct clinical management.

Development and validation of an ELISA kit (YF MAC-HD) to detect IgM to yellow fever virus

Yellow fever virus (YFV) is endemic in tropical and sub-tropical regions of the world, with around 180,000 human infections a year occurring in Africa. Serologic testing is the chief laboratory diagnostic means of identifying an outbreak and to inform the decision to commence a vaccination campaign. The World Health Organization disseminates the reagents for YFV testing to African reference laboratories, and the US Centers for Disease Control and Prevention (CDC) is charged with producing and providing these reagents. The CDC M-antibody capture ELISA is a 2-day test, requiring titration of reagents when new lots are received, which leads to inconsistency in testing and wastage of material. Here we describe the development of a kit-based assay (YF MAC-HD) based upon the CDC method, that is completed in approximately 3.5h, with equivocal samples being reflexed to an overnight protocol. The kit exhibits >90% accuracy when compared to the 2-day test. The kits were designed for use with a minimum of equipment and are stored at 4°C, removing the need for freezing capacity. This kit is capable of tolerating temporary sub-optimal storage conditions which will ease shipping or power outage concerns, and a shelf life of >6 months was demonstrated with no deterioration in accuracy. All reagents necessary to run the YF MAC-HD are included in the kit and are single-use, with 8 or 24 sample options per kit. Field trials are envisioned for the near future, which will enable refinement of the method. The use of the YF MAC-HD is anticipated to reduce materials wastage, and improve the quality and consistency of YFV serologic testing in endemic areas.

Evaluation of a rapid analyte measurement platform and real-time reverse-transcriptase polymerase chain reaction assay West Nile virus detection system in mosquito pools.

Abstract We evaluated the commercially available Rapid Analyte Measurement Platform (RAMP®) West Nile virus (WNV) antigen detection test for sensitivity and consistency with real-time reverse transcriptase polymerase chain reaction (RT-PCR) confirmation testing. Panels of samples consisting of WNV-spiked mosquito pools and negative control pools were sent to 20 mosquito abatement districts (MADs) that processed the pools using the RAMP assay. The samples were then sent to the reference laboratories used by the MADs for confirmation by real-time RT-PCR. Positive pools with virus titers of roughly 1–3 log10 PFU/ml had RAMP scores above the RAMP test positive cutoff score of 30 RAMP units, but these virus-positive samples could not be reliably confirmed by real-time RT-PCR testing. Pools with virus titers ≥4 log10 PFU/ml scored ≥50 RAMP units. Real-time RT-PCR results varied among the confirmation laboratories. With few exceptions, pools returning a RAMP score of ≥100 were confirmed with real-time RT-PCR, while pools returning a RAMP score of 50–99 appeared to be at the limit of real-time RT-PCR detection. Therefore, we recommend using a positive cutoff of 50 RAMP units with no real-time RT-PCR confirmation to maximize speed, efficiency, and economy of the RAMP assay. A more conservative approach would be to implement a “gray zone” range of 50–100 RAMP units. Pools scoring within the gray zone could be submitted for real-time RT-PCR confirmation with the understanding that positive pools may not confirm due to the inhibitory effect of the RAMP buffer on the real-time RT-PCR assay. We also conducted a series of experiments using laboratory-prepared mosquito pools spiked with WNV to compare mosquito homogenization buffers, pool sizes, and grinding methods in order to determine how these variables affect the RAMP and real-time RT-PCR assay results.

Effect of Aerial Insecticide Spraying on West Nile Virus Disease—North-Central Texas, 2012

During 2012, four north-central Texas counties experienced high West Nile virus (WNV) disease incidence. Aerial insecticide spraying was conducted in two counties. To evaluate the effect of spraying on WNV disease, we calculated incidence rate ratios (IRRs) in treated and untreated areas by comparing incidence before and after spraying; for unsprayed areas, before and after periods were defined by using dates from a corresponding sprayed area. In treated areas, WNV neuroinvasive disease incidence before and after spraying was 7.31/100,000 persons and 0.28/100,000 persons, respectively; the IRR was 26.42 (95% confidence interval [CI]: 12.42-56.20). In untreated areas, the before and after incidence was 4.80/100,000 persons and 0.45/100,000 persons, respectively; the IRR was 10.57 (95% CI: 6.11-18.28). The ratio of IRRs was 2.50 (95% CI: 0.98-6.35). Disease incidence decreased in both areas, but the relative change was greater in aerial-sprayed areas.