The IgM-PRNT90 titers for samples 52A and 54A decreased to 10 for all three viruses, which was not surprising, considering that both of the samples had equivocal or nondetectable IgM results for ZIKV and DENV by ELISA (Table 4)

The IgM-PRNT90 titers for samples 52A and 54A decreased to 10 for all three viruses, which was not surprising, considering that both of the samples had equivocal or nondetectable IgM results for ZIKV and DENV by ELISA (Table 4). primary and secondary flaviviral infections acquired when visiting areas experiencing active ZIKV transmission in 2015 and 2016. Specimens collected between 1 day and 3 months postexposure were tested for ZIKV and dengue virus type 1 (DENV1) and type 2 (DENV2) by the plaque reduction neutralization test (PRNT) before and after IgG depletion. We found that IgG depletion prior to neutralization testing had little effect in differentiating samples from individuals with secondary infections taken less than 3 weeks postexposure; however, IgG depletion significantly reduced the cross-reactive neutralizing antibody titers and increased the percentage of cases discernible by PRNT from 15.4% (95% confidence interval [CI], 4.3 to IL5RA 42.2%) to 76.9% (95% CI, 49.7 to 91.8%) for samples collected between roughly 3 and 12 weeks postexposure. These results highlight the potential of IgG depletion to improve the specificity of PRNT for better confirmation and differential diagnosis of flavivirus infections. KEYWORDS: Zika virus, confirmatory testing, dengue virus, flavivirus, immunoglobulin M, neutralization test, neutralizing antibodies, serological testing INTRODUCTION Zika virus (ZIKV) is a Inolitazone dihydrochloride mosquito-borne virus (genus mosquito. ZIKV was first isolated in 1947 from the blood of a febrile sentinel rhesus monkey during a study of yellow fever in the Zika Forest, Uganda (1). Other notable viruses in this genus make up several serocomplexes, including the dengue virus (DENV), the tick-borne encephalitis virus (TBEV), the Japanese encephalitis virus (JEV), and the yellow fever virus (YFV) serocomplexes. ZIKV is categorized Inolitazone dihydrochloride in the Spondweni serocomplex, of which only ZIKV and Spondweni virus (SPONV) are members. ZIKV causes a mild febrile illness with symptoms very similar to the symptoms caused by infection with DENV. There is only transient cross-protection among the 4 DENV serotypes (DENV serotype 1 [DENV1] to DENV4); hence, individuals can be infected with multiple types of DENV in their lifetimes. Given their common mosquito vector, ZIKV has recently emerged Inolitazone dihydrochloride and spread across many areas where DENV is endemic. Therefore, in addition to secondary infection by DENV (for example, DENV1 and then DENV2), cases of secondary infection by ZIKV following a prior DENV infection have emerged in many areas. While ZIKV and DENV1 to DENV4 are not in the same serocomplex, they do share 53 to 57% amino acid sequence identity in the envelope (E) protein, the viral structural protein responsible for eliciting the majority of flavivirus cross-reactive antibodies (2,C6). Many studies have shown that antibodies isolated from persons with previous DENV exposure can cross-neutralize ZIKV = 15), panel 2 is in gray (= 24 for DENV1, = 25 for DENV2), and panel 3 has diagonal lines (= 22 for DENV1, = 23 for DENV2). Average ratios of the neutralization test titers (for the WT virus to the chimera) are shown with standard errors. The dashed line at a ratio of 0.5 represents a 2-fold decrease in the PRNT90 titer of WT viruses compared to that for the chimeric viruses. Diagnostic specimens. We obtained ethics approval for use of previously collected human diagnostic specimens from the CDC’s Human Subjects Institutional Review Board (CDC IRB number 6773). Thirty-three specimens from patients with a possible recent flaviviral infection were randomly selected and acquired from CDC’s Arboviral Diseases Branch diagnostic laboratory. These samples included specimens collected from asymptomatic pregnant women (designated with an A after the sample identification number) with a recent travel history to areas where ZIKV transmission was known to occur in 2015 and 2016. Due to an unclear virus exposure time and the various travel periods of these subjects, we calculated the post-median travel time (PMT) points for samples from asymptomatic individuals from the median day of the travel period to the sample collection date to estimate their potential postexposure time points. For symptomatic subjects, the sample collection time post-symptom onset (PSO; based on the subject’s memory of any suspected symptoms during travel) was used to indicate the potential postexposure time. Many Inolitazone dihydrochloride subjects frequently visited or stayed in areas where DENV is endemic and that were also affected by the recent ZIKV outbreak. Therefore, some of them may have had previous exposure to 1 or more DENVs.