Enzyme-linked immunosorbent assays using recombinant envelope protein expressed in COS-1 and Drosophila S2 cells for detection of West Nile virus immunoglobulin M in serum or cerebrospinal fluid

Mosquito Defensins Enhance Japanese Encephalitis Virus Infection by Facilitating Virus Adsorption and Entry within the Mosquito

Japanese encephalitis virus (JEV) is a viral zoonosis that can cause viral encephalitis, death, and disability. Although the Culex mosquito is the primary vector of JEV, little is known about JEV transmission by this kind of mosquito. Here, we found that mosquito defensin facilitated the adsorption of JEV on target cells via the defensin/lipoprotein receptor-related protein 2 (LRP2) axis. Mosquito defensin bound the ED III domain of the viral envelope (E) protein and directly mediated efficient virus adsorption on the target cell surface; the receptor LRP2, which is expressed on the cell surface, affected defensin-dependent adsorption. As a result, mosquito defensin enhanced JEV infection in the salivary gland, increasing the possibility of viral transmission by mosquitoes. These findings demonstrate the novel role of mosquito defensin in JEV infection and the mechanisms through which the virus exploits mosquito defensin for infection and transmission.IMPORTANCE In this study, we observed the complex roles of mosquito defensin in JEV infection; mosquito defensin exhibited a weak antiviral effect but strongly enhanced binding. In the latter, defensin directly binds the ED III domain of the viral E protein and promotes the adsorption of JEV to target cells by interacting with lipoprotein receptor-related protein 2 (LRP2), thus accelerating virus entry. Together, our results indicate that mosquito defensin plays an important role in facilitating JEV infection and potential transmission.

Indigenous West Nile virus infections in horses in Albania

Serum samples collected from 167 equines of 12 districts in Albania were tested for West Nile virus-specific antibodies by enzyme-linked immunosorbent assay and virus neutralization assay, using WNV lineage 1 and 2. In addition, 95 bird serum samples from Albania and 29 horse samples from Kosovo were tested in ELISA. An overall seroprevalence rate of 22% was found in horses from Albania, whereas no specific antibodies were found in the equine samples from Kosovo and the bird samples. This is the first report indicating WNV infections in animals in Albania, and the first reported seroprevalence study conducted for Kosovo. These results provide evidence for widespread infections of WNV in Albania.

West Nile virus: A re-emerging pathogen revisited

West Nile virus (WNV), a flavivirus of the Flaviviridae family, is maintained in nature in an enzootic transmission cycle between avian hosts and ornithophilic mosquito vectors, although the virus occasionally infects other vertebrates. WNV causes sporadic disease outbreaks in horses and humans, which may result in febrile illness, meningitis, encephalitis and flaccid paralysis. Until recently, its medical and veterinary health concern was relatively low; however, the number, frequency and severity of outbreaks with neurological consequences in humans and horses have lately increased in Europe and the Mediterranean basin. Since its introduction in the Americas, the virus spread across the continent with worrisome consequences in bird mortality and a considerable number of outbreaks among humans and horses, which have resulted in the largest epidemics of neuroinvasive WNV disease ever documented. Surprisingly, its incidence in human and animal health is very different in Central and South America, and the reasons for it are not yet understood. Even though great advances have been obtained lately regarding WNV infection, and although efficient equine vaccines are available, no specific treatments or vaccines for human use are on the market. This review updates the most recent investigations in different aspects of WNV life cycle: molecular virology, transmission dynamics, host range, clinical presentations, epidemiology, ecology, diagnosis, control, and prevention, and highlights some aspects that certainly require further research.

Evaluation of an enzyme-linked immunosorbent assay for detection of West Nile virus infection based on a recombinant envelope protein produced in Trichoplusia ni larvae

West Nile virus (WNV), a Flavivirus distributed most widely, is presenting lately variable epidemiological and ecological patterns, including an increasing virulence that has already caused over 1000 human deaths in USA. Currently, diagnosis of WNV is achieved mainly by enzyme-linked immunoassays (ELISAs) based on the use of inactivated whole WNV (iWNV) as antigen, although results have to be confirmed by plaque reduction neutralization tests (PRNTs). Expression of WNV envelope recombinant E (rE) protein and its usefulness as ELISA antigen are described. Production of rE was achieved upon infection of Trichoplusia ni insect larvae with a recombinant baculovirus. Once optimized, the rE-based ELISA was validated with a battery of mouse and equine sera characterized previously. Concordance with the iWNV-based ELISA used routinely was good (95%), as it was with the reference PRNT (90%), with specificity of 94.4% and sensitivity of 88.1%. Production of rE protein in insect larvae allows for an easy, low cost and quite large-scale yield of partially purified antigen which is suitable for serological diagnosis of WNV, without the need for manipulation of large quantities of infective virus.

In vitro evaluation of the protective role of human antibodies to West Nile virus (WNV) produced during natural WNV infection

BACKGROUND

West Nile virus (WNV) is endemic in the United States and transmissible by transfusion. Since 2003, the US blood supply has been screened by nucleic-acid tests (NAT) for WNV in minipools (MP-NAT) of 6 or 16 specimens. WNV infection begins with low-level viremia detectable only by individual testing (ID-NAT) and no detectable WNV antibodies. Viremia then increases to levels detectable by MP-NAT, and antibodies become detectable; later, viremia decays to levels detectable only by ID-NAT before becoming undetectable. All but 1 documented WNV transmission by transfusion involved blood components negative for WNV antibodies, raising the question whether WNV antibody-positive blood components with low levels of WNV RNA are infectious.

METHODS

Specimens from 102 viremic donors with and without WNV antibodies were used to investigate infectivity in cultures of Vero cells and human monocyte-derived macrophages (MDMs).

RESULTS

In Vero cell culture, 54 (74%) of 73 WNV antibody-negative specimens and 10 (36%) of 28 WNV antibody-positive specimens were infectious. In a random subset of 20 specimens tested in MDM culture, 7 (88%) of 8 WNV antibody-positive specimens and 12 (100%) of 12 WNV antibody-negative specimens were infectious.

CONCLUSION

WNV antibodies do not always protect susceptible cells from WNV infection in vitro. RNA positivity in the presence of antibody cannot be ignored as a theoretical risk for blood recipients and needs further investigation.

T7 phage display of Ep15 peptide for the detection of WNV IgG

West Nile virus (WNV) is one of the major emerging infectious diseases in North America. WNV belongs to the genus Flavivirus, and its rapid and extensive global spread has highlighted the necessity for accurate and specific assays for diagnosis of WNV infection. This study presents the first phage displayed peptide based ELISA for detection of WNV immunoglobulin G (IgG). The Ep15 epitope, derived from the WNV E protein DIII, was cloned into a T7 phage display system that was then used as recombinant antigen in a chemiluminescent ELISA format. The phage concentration was optimized at 5 x 10(10)PFU/ml and was used directly after polyethylene glycol concentration. The assay shows a limit of detection at a serum titer of 1:51,200 and a dynamic range from 1:100 to 1:2000. A screen of a panel of 66 human sera samples, and comparison with a commercial kit, revealed a sensitivity of 67% and a specificity of 100%. Considering the ease of antigen preparation, its stability and the optimum display properties of the T7 bacteriophage, it is apparent that this approach can be useful for the preparation of highly sensitive and specific anti-WNV immunoglobulin diagnostic kits.

West Nile virus: recent trends in diagnosis and vaccine development

West Nile virus (WNV) is a mosquito-borne flavivirus, native to Africa, Europe, and Western Asia. In many respects, WNV is an outstanding example of a zoonotic pathogen that has leaped geographical barriers and can cause severe disease in human and horse. Before the emergence of WNV in the USA, only few methods of diagnosis were available. Recently, many changes in the fields of WN diagnosis and prevention have happened. This paper will review all these new tools. After a description of the main concerns in WNV and West Nile (WN) disease in humans and animals, this review will present the main available tests for serology and virology detection, from gold standard tests to more recently developed methods. Finally, licensed vaccines and candidate vaccines developed in humans, horses and birds will also been described.

Monoclonal antibody-based competitive enzyme-linked immunosorbent assay for detecting and quantifying West Nile virus-neutralizing antibodies in horse sera

A rapid immunoassay for detecting and quantifying West Nile virus (WNV)-neutralizing antibodies in sera was developed as an alternative to the plaque reduction neutralization test (PRNT), the gold standard test for WNV. The assay is a competitive, enzyme-linked immunosorbent assay using neutralizing monoclonal antibody 5E8 (NT-ELISA). A cutoff percent inhibition (PI) value of 35% (mean PI plus 3 standard deviations), with a specificity of 99%, was established based on analysis of 246 serum samples from horses free of WNV. The NT-ELISA detected neutralizing antibodies in all sera collected 7 or 14 days postinoculation from mice (n = 11) infected with lineage I (strain NY385-99) or II (strain B956) WNV. When sera from WNV-vaccinated horses (n = 212) were tested by NT-ELISA and PRNT, the NT-ELISA gave a positive result for 96.1% (173/180) of the PRNT-positive sera and 3.1% (1/32) of the PRNT-negative sera. Discrepancies between the two tests were observed mainly with sera with low PRNT(90) titers (expressed as the reciprocal of the highest dilution yielding > or = 90% reduction in the number of plaques) for WNV or low PIs by NT-ELISA. The overall agreement (k value) between the two tests was 0.86. A good correlation (r(2) = 0.77) was also observed between the tests for endpoint titration of sera (n = 116). In conclusion, the newly developed NT-ELISA may be a good alternative serologic assay for detecting WNV that can be used for large-scale testing of WNV-neutralizing antibodies in multiple species.