Prolonged Shedding of Zika Virus RNA in Vaginal Secretions, Nicaragua.

Zika virus, an arthropod-borne flavivirus pathogen in humans, is unusual because it can be sexually transmitted and can be shed for prolonged periods in semen. We report viral shedding in vaginal secretions for up to 6 months, indicating the potential for sexual and vertical transmission by infected women.

Development of Envelope Protein Antigens To Serologically Differentiate Zika Virus Infection from Dengue Virus Infection.

Zika virus (ZIKV) is an emerging flavivirus that can cause birth defects and neurologic complications. Molecular tests are effective for diagnosing acute ZIKV infection, although the majority of infections produce no symptoms at all or present after the narrow window in which molecular diagnostics are dependable. Serology is a reliable method for detecting infections after the viremic period; however, most serological assays have limited specificity due to cross-reactive antibodies elicited by flavivirus infections. Since ZIKV and dengue virus (DENV) widely cocirculate, distinguishing ZIKV infection from DENV infection is particularly important for diagnosing individual cases or for surveillance to coordinate public health responses. Flaviviruses also elicit type-specific antibodies directed to non-cross-reactive epitopes of the infecting virus; such epitopes are attractive targets for the design of antigens for development of serological tests with greater specificity. Guided by comparative epitope modeling of the ZIKV envelope protein, we designed two recombinant antigens displaying unique antigenic regions on domain I (Z-EDI) and domain III (Z-EDIII) of the ZIKV envelope protein. Both the Z-EDI and Z-EDIII antigens consistently detected ZIKV-specific IgG in ZIKV-immune sera but not cross-reactive IgG in DENV-immune sera in late convalescence (>12 weeks postinfection). In contrast, during early convalescence (2 to 12 weeks postinfection), secondary DENV-immune sera and some primary DENV-immune sera cross-reacted with the Z-EDI and Z-EDIII antigens. Analysis of sequential samples from DENV-immune individuals demonstrated that Z-EDIII cross-reactivity peaked in early convalescence and declined steeply over time. The Z-EDIII antigen has much potential as a diagnostic antigen for population-level surveillance and for detecting past infections in patients.

Clinical and Epidemiological Features of Acute Zika Virus Infections in León, Nicaragua.

The American Zika virus (ZIKV) epidemic has highlighted the need to gain a better understanding of this emerging virus. The goal of this study was to describe the clinical symptoms, laboratory findings, and risk factors for symptomatic ZIKV infection in an area with ongoing transmission of other arboviral infections. We recruited patients at least 2 years of age seeking care at public health centers in León, Nicaragua, between January 2016 and August 2017, for fever, maculopapular rash, and/or nonsuppurative conjunctivitis with a duration of less than 1 week. A laboratory diagnosis of ZIKV was established using a combination of molecular and serological tests. Clinical and laboratory findings and potential risk factors were compared between participants with and without acute ZIKV infection. Fifty-eight (26%) of the 225 participants included in the analysis were found to have acute ZIKV infection. Pregnancy and reports of previous arboviral infection were associated with a higher risk of ZIKV infection. Rash, conjunctivitis, sore throat, and lower absolute neutrophil counts were associated with acute ZIKV infection. The clinical characteristics and risk factors identified were consistent with those identified by previous studies; however, we found sore throat to be a feature of ZIKV infection. We also found that neutrophil counts were lower in ZIKV-infected subjects. These clinical symptoms and laboratory data may help clinicians suspect ZIKV infection during future outbreaks.

Serologic surveillance of maternal Zika infection in a prospective cohort in Leon, Nicaragua during the peak of the Zika epidemic.

BACKGROUND: Zika virus caused thousands of congenital anomalies during a recent epidemic. Because Zika emerged in areas endemic for dengue and these related flaviviruses elicit cross-reactive antibodies, it is challenging to serologically monitor pregnant women for Zika infection. METHODS: A prospective cohort of 253 pregnant women was established in León, Nicaragua. Women were followed during prenatal care through delivery. Serologic specimens were obtained at each visit, and birth outcome was recorded. Established flavivirus serologic methods were adapted to determine Zika seroprevalence, and a stepwise testing algorithm estimated timing of Zika infection in relation to pregnancy. RESULTS: Zika seroprevalence was approximately 59% among women tested. Neutralization testing was highly concordant with Zika NS1 BOB results. Per study algorithm, 21% (40/187) of women were classified as experiencing Incident ZIKV infection during pregnancy. Importantly, the Incident ZIKV group included mostly women pregnant during the 2016 Zika epidemic peak and the only 3 subjects in the cohort with RT-PCR-confirmed infections. Approximately 17% of births had complications; 1.5% (3/194) manifesting clinical criteria of congenital Zika syndrome, one was RT-PCR-confirmed as a case of congenital Zika syndrome. Adverse birth outcome did not correlate with timing of Zika infection. CONCLUSIONS: By leveraging prenatal care systems, we developed a simple algorithm for identifying women who were likely infected by Zika during pregnancy.

Human antibody response to Zika targets type-specific quaternary structure epitopes.

The recent Zika virus (ZIKV) epidemic in the Americas has revealed rare but serious manifestations of infection. ZIKV has emerged in regions endemic for dengue virus (DENV), a closely related mosquito-borne flavivirus. Cross-reactive antibodies confound studies of ZIKV epidemiology and pathogenesis. The immune responses to ZIKV may be different in people, depending on their DENV immune status. Here, we focus on the human B cell and antibody response to ZIKV as a primary flavivirus infection to define the properties of neutralizing and protective antibodies generated in the absence of preexisting immunity to DENV. The plasma antibody and memory B cell response is highly ZIKV type-specific, and ZIKV-neutralizing antibodies mainly target quaternary structure epitopes on the viral envelope. To map viral epitopes targeted by protective antibodies, we isolated 2 type-specific monoclonal antibodies (mAbs) from a ZIKV case. Both mAbs were strongly neutralizing in vitro and protective in vivo. The mAbs recognize distinct epitopes centered on domains I and II of the envelope protein. We also demonstrate that the epitopes of these mAbs define antigenic regions commonly targeted by plasma antibodies in individuals from endemic and nonendemic regions who have recovered from ZIKV infections.