[Flavivirus seroepidemiology in blood donors in Mersin province, Turkey]

Among the vector-borne flaviviruses, West Nile virus (WNV), tick-borne encephalitis virus (TBEV) and Dengue virus (DENV) constitute the most frequently-observed pathogens with significant public health impact in endemic regions throughout the globe. This seroepidemiological study was undertaken to investigate human exposure to DENV, WNV and TBEV, as well as other flaviviruses via various serological assays in the Mediterranean province of Mersin, Turkey, where scarce data is currently present for the circulation of these agent. A total of 920 sera were collected after informed consent from asymptomatic blood donors (all were male; age range: 18-63 yrs, mean age: 35.17 ± 9.56 yrs) were taken between August 2010 and April 2011. All samples were initially screened via a commercial ELISA kit for DENV IgM and IgG. Reactive samples were further evaluated via commercial indirect immunofluorescence tests (IIFTs) for yellow fever virus (YFV) IgG, TBEV IgG and via ELISA for WNV IgG. Moreover, presence of neutralizing antibodies were investigated in all reactive samples via plaque reduction neutralization (PRNT) assay for WNV, whose activity has been detected previously in the region. Samples interpreted as positive for TBEV IgG were further evaluated for specificity by TBEV PRNT assay. DENV IgM reactive samples were also assessed for NS1 antigens and IgM/IgG antibodies via a commercial immunochromatographic assay (ICA). DENV IgM and IgG antibodies were detected in 0.9% (8/920) and 16.6% (153/920) of the samples, respectively. One sample was simultaneously positive for IgM and IgG. WNV PRNT revealed positive results in 85.6% (137/160) of the reactive samples, which indicated frequent WNV exposure and frequent development of cross-reactions in the screening assay. Positive or borderline DENV IgM reactivity was identified in 0.43% (4/920) of the samples, which remained negative for NS1 antigen and antibodies in the ICA. Antibody specificity in two samples, positive for DENV and TBEV IgG in IIFT could not be confirmed by TBEV PRNT. A total of 19 reactive samples (19/920, 2.1%), that comprise seven borderline and six positive DENV IgG positivities as well as six samples with IgG positivity for different virus combinations remained negative after DENV confirmatory and WNV/TBEV PRNT assays. When the samples with borderline results were omitted from the evaluation, 12 samples (12/920, 1.3%) were considered to represent exposure to DENV or an antigenically-similar flavivirus. These findings indicated the activity of and frequent exposure (137/920, 14.9%) to WNV, as previously suggested in the study region. In 1.3% of the samples, probable exposure to DENV or other flaviviruses was revealed and this requires further serosurveillance efforts. WNV must be considered in the etiology of febrile diseases or viral neuroinvasive infections of unexplained etiology in the study area.