Zika virus (ZIKV) is a mosquito-borne flavivirus that emerged recently as a global health threat, causing a pandemic in the Americas. ZIKV infection mostly causes mild disease, but is linked to devastating congenital birth defects and Guillain-Barré syndrome in adults. The high level of cross-reactivity among flaviviruses and their cocirculation has complicated serological approaches to differentially detect ZIKV and dengue virus (DENV) infections, accentuating the urgent need for a specific and sensitive serological test. We previously generated a ZIKV nonstructural protein 1 (NS1)-specific human monoclonal antibody, which we used to develop an NS1-based competition ELISA. Well-characterized samples from RT-PCR-confirmed patients with Zika and individuals exposed to other flavivirus infections or vaccination were used in a comprehensive analysis to determine the sensitivity and specificity of the NS1 blockade-of-binding (BOB) assay, which was established in laboratories in five countries (Nicaragua, Brazil, Italy, United Kingdom, and Switzerland). Of 158 sera/ plasma from RT-PCR-confirmed ZIKV infections, 145 (91.8%) yielded greater than 50% inhibition. Of 171 patients with primary or secondary DENV infections, 152 (88.9%) scored negative. When the control group was extended to patients infected by other flaviviruses, other viruses, or healthy donors (n = 540), the specificity was 95.9%. We also analyzed longitudinal samples from DENV-immune and DENVnaive ZIKV infections and found inhibition was achieved within 10 d postonset of illness and maintained over time. Thus, the Zika NS1 BOB assay is sensitive, specific, robust, simple, low-cost, and accessible, and can detect recent and past ZIKV infections for surveillance, seroprevalence studies, and intervention trials.is a mosquito-borne flavivirus that is spread via the bite of infected Aedes mosquitoes or by sexual transmission and is responsible for the explosive 2015-2017 epidemic in the Americas. ZIKV infection during pregnancy is linked to devastating birth defects and associated anomalies, designated congenital Zika syndrome (1, 2), whereas in adults, ZIKV infection has been associated with Guillain Barré syndrome (3). Flaviviruses are enveloped RNA viruses containing an ∼11-kb positive-stranded RNA genome that encodes three structural and seven nonstructural proteins. Cells infected by flaviviruses secrete nonstructural protein 1 (NS1), which has multiple roles in immune evasion and pathogenesis (4, 5).Antibody responses generated in response to flavivirus infections are notoriously cross-reactive, representing a significant obstacle for the specific diagnosis of infection using serological assays. Multiple RT-PCR-based assays for the detection of ZIKV RNA are available, but their use is limited to the narrow window when viral RNA is detectable in body fluids. This is highly variable among patients and subject to reporting error, as symptoms are mild, and thus patients may take less notice of the day of onset, but in most cases, it is up to 7 d in serum, ...

In endemic areas, ZIKV should be considered as an aetiological agent in cases of encephalitis, and clinicians should be aware of its potential severity.

BackgroundDuring 2015–16 Brazil experienced the largest epidemic of Zika virus ever reported. This arthropod-borne virus (arbovirus) has been linked to Guillain-Barré syndrome (GBS) in adults but other neurological associations are uncertain. Chikungunya virus has caused outbreaks in Brazil since 2014 but associated neurological disease has rarely been reported here. We investigated adults with acute neurological disorders for Zika, chikungunya and dengue, another arbovirus circulating in Brazil.MethodsWe studied adults who had developed a new neurological condition following suspected Zika virus infection between 1st November 2015 and 1st June 2016. Cerebrospinal fluid (CSF), serum, and urine were tested for evidence of Zika, chikungunya, and dengue viruses.ResultsOf 35 patients studied, 22 had evidence of recent arboviral infection. Twelve had positive PCR or IgM for Zika, five of whom also had evidence for chikungunya, three for dengue, and one for all three viruses. Five of them presented with GBS; seven had presentations other than GBS, including meningoencephalitis, myelitis, radiculitis or combinations of these syndromes. Additionally, ten patients positive for chikungunya virus, two of whom also had evidence for dengue virus, presented with a similar range of neurological conditions.ConclusionsZika virus is associated with a wide range of neurological manifestations, including central nervous system disease. Chikungunya virus appears to have an equally important association with neurological disease in Brazil, and many patients had dual infection. To understand fully the burden of Zika we must look beyond GBS, and also investigate for other co-circulating arboviruses, particularly chikungunya.