Seroprevalence of arboviruses among blood donors in French Polynesia, 2011–2013

Objectives: French Polynesia is a high epidemic/endemic area for arthropod-borne viruses (arboviruses). We recently reported the silent circulation of Ross River virus and absence of active transmission of chikungunya virus (CHIKV) among blood donors sampled before the emergence of Zika virus (ZIKV) and CHIKV in French Polynesia. In this study, the prevalence of the four serotypes of dengue virus (DENV) and the occurrence of circulation of other arboviruses were investigated in blood donors in French Polynesia. Methods: Serum samples from 593 blood donors collected between July 2011 and October 2013 were tested by ELISA for the presence of immunoglobulin G antibodies against each of the four DENV serotypes, ZIKV, Japanese encephalitis virus (JEV), and West Nile virus (WNV). Results: It was found that 80.3%, 0.8%, 1.3%, and 1.5% of blood donors were seropositive for at least one DENV serotype, ZIKV, JEV, and WNV, respectively. Conclusions: These results corroborate the expected high transmission of DENV and conversely suggest that no active circulation of ZIKV, JEV, and WNV occurred in French Polynesia before 2011. Information provided by this study may be useful for public health authorities to improve surveillance and implement strategies to prevent the transmission of arboviruses

A High-Performance Multiplex Immunoassay for Serodiagnosis of Flavivirus-Associated Neurological Diseases in Horses

West Nile virus (WNV), Japanese encephalitis virus (JEV), and tick-borne encephalitis virus (TBEV) are flaviviruses responsible for severe neuroinvasive infections in humans and horses. The confirmation of flavivirus infections is mostly based on rapid serological tests such as enzyme-linked immunosorbent assays (ELISAs). These tests suffer from poor specificity, mainly due to antigenic cross-reactivity among flavivirus members. Robust diagnosis therefore needs to be validated through virus neutralisation tests (VNTs) which are time-consuming and require BSL3 facilities. The flavivirus envelope (E) glycoprotein ectodomain is composed of three domains (D) named DI, DII, and DIII, with EDIII containing virus-specific epitopes. In order to improve the serological differentiation of flavivirus infections, the recombinant soluble ectodomain of WNV E (WNV.sE) and EDIIIs (rEDIIIs) of WNV, JEV, and TBEV were synthesised using the Drosophila S2 expression system. Purified antigens were covalently bonded to fluorescent beads. The microspheres coupled to WNV.sE or rEDIIIs were assayed with about 300 equine immune sera from natural and experimental flavivirus infections and 172 nonimmune equine sera as negative controls. rEDIII-coupled microspheres captured specific antibodies against WNV, TBEV, or JEV in positive horse sera. This innovative multiplex immunoassay is a powerful alternative to ELISAs and VNTs for veterinary diagnosis of flavivirus-related diseases

Silent Circulation of Ross River Virus in French Polynesia

Objectives: Ross River is an emerging mosquito-borne disease in the Western Pacific. Ross River virus (RRV) circulation has been sporadically reported in some Pacific Island Countries and Territories but never in French Polynesia. To determine if RRV has circulated locally among the French Polynesian population, we conducted a seroprevalence study on blood donors. Methods: Sera of 593 blood donors were collected from July 2011 to October 2013 and tested by ELISA for the presence of RRV-specific Immunoglobulin G (IgG) antibodies. Results: A total of 204 (34.40%) blood donors were found seropositive for RRV. Among the 132 blood donors that were born in French Polynesia and had never travelled abroad, 56 (42.42%) had RRV-specific IgGs. Discussion: Our results support the existence of autochthonous RRV transmission and suggest that this pathogen has silently circulated in French Polynesia. These findings raise the question of possible undetected circulation of RRV in other Pacific Island Countries and Territories

A Lentiviral Vector Expressing Japanese Encephalitis Virus-like Particles Elicits Broad Neutralizing Antibody Response in Pigs.

BACKGROUND Japanese encephalitis virus (JEV) is the major cause of viral encephalitis in Southeast Asia. Vaccination of domestic pigs has been suggested as a "one health" strategy to reduce viral disease transmission to humans. The efficiency of two lentiviral TRIP/JEV vectors expressing the JEV envelope prM and E glycoproteins at eliciting protective humoral response was assessed in a mouse model and piglets. METHODOLOGY/PRINCIPAL FINDINGS A gene encoding the envelope proteins prM and E from a genotype 3 JEV strain was inserted into a lentiviral TRIP vector. Two lentiviral vectors TRIP/JEV were generated, each expressing the prM signal peptide followed by the prM protein and the E glycoprotein, the latter being expressed either in its native form or lacking its two C-terminal transmembrane domains. In vitro transduction of cells with the TRIP/JEV vector expressing the native prM and E resulted in the efficient secretion of virus-like particles of Japanese encephalitis virus. Immunization of BALB/c mice with TRIP/JEV vectors resulted in the production of IgGs against Japanese encephalitis virus, and the injection of a second dose one month after the prime injection greatly boosted antibody titers. The TRIP/JEV vectors elicited neutralizing antibodies against JEV strains belonging to genotypes 1, 3, and 5. Immunization of piglets with two doses of the lentiviral vector expressing JEV virus-like particles led to high titers of anti-JEV antibodies, that had efficient neutralizing activity regardless of the JEV genotype tested. CONCLUSIONS/SIGNIFICANCE Immunization of pigs with the lentiviral vector expressing JEV virus-like particles is particularly efficient to prime antigen-specific humoral immunity and trigger neutralizing antibody responses against JEV genotypes 1, 3, and 5. The titers of neutralizing antibodies elicited by the TRIP/JEV vector are sufficient to confer protection in domestic pigs against different genotypes of JEV and this could be of a great utility in endemic regions where more than one genotype is circulating

New evidence for endemic circulation of Ross River virus in the Pacific Islands and the potential for emergence

Objectives: An epidemic of Ross River virus (RRV) occurred in the South Pacific in 1979–1980, but RRV has not been thought to occur endemically outside Australia and Papua New Guinea. A seroprevalence study was conducted to determine whether RRV has circulated in American Samoa since 1980. Methods: RRV ELISA IgG was performed on 200 serum samples collected in American Samoa in 2010; seroneutralization tests were performed on 60 representative samples. Results: Of 196 available ELISA IgG results, 145 (74%, 95% confidence interval 67–80%) were seropositive. Of the 60 samples subjected to seroneutralization testing, none of the 15 ELISA IgG-negative and 16 of the 45 ELISA IgG-positive samples neutralized RRV. ELISA IgG seroprevalence was higher in persons born before/during the 1979–1980 RRV outbreak (78.3%), but was also high (63.0%) in people born after the outbreak who had lived their entire lives in American Samoa. Conclusions: This study provides serological evidence that RRV circulation is likely to have occurred in American Samoa after 1980. Considering there are no marsupials in American Samoa, this finding implies that other species are capable of acting as reservoir hosts and indicates the potential for RRV to circulate in a much wider area than those currently recognized

Protective capacity of TRIP/JEV antisera in a mouse model.

<p>Groups of 3-week-old C56BL/6 mice received i.p. inoculation with 0.1 ml of DPBS containing 0.01 ml of pooled immune sera collected from JEV-infected mice (JEV G3 antiserum) or TRIP/JEV-inoculated mice two months after boosting. Mice inoculated with DPBS (PBS) served as a group control. One day later, the mice were i.p. challenged with JEV strain RP-9 and observed daily for mortality. Survival was recorded for 21 days. The asterisk indicates that the differences between survival curves are statistically significant (*, <i>P</i> < 0.05, n.s.: <i>P</i> > 0.05).</p