DENGUE PRE EXISTING ANTIBODIES DO NOT SUPPORT ADE OF ZIKV IN RHESUS MACAQUES

Zika virus (ZIKV) (Flaviviridae) is an emerging mosquito-borne virus reported in the Americas since 2014, with a major outbreak in Brazil in 2015. It has spread to at least 38 countries in the Americas and Caribbean. This outbreak has been associated to neurological sequelae, prompting the World Health Organization to declare it a public health emergency. ZIKV infection has occurred in areas previously exposed to dengue virus (DENV), a closely related flavivirus. One feature of DENV infection is that the more severe clinical presentations are common after secondary infection. This has been explained by different mechanisms including the antibody-dependent enhancement (ADE) hypothesis, which suggests that antibodies generated during a primary infection will not be of sufficient concentration or avidity to neutralize a secondary infection with a different serotype. ADE has shown to drive higher viral loads of DENV in animal models. Since ZIKV is close related to DENV with a homology of 51-54% in the envelope amino acid sequence, we wanted to know if previous exposition to DENV virus predispose to severe forms of ZIKV infection in non-human primates (NHP), reproducing the circumstances under which ZIKV is introduced into DENV endemic areas. We used NHP with a previous exposition to a single DENV serotype (1 or 2) and no exposition to ZIKV. Another cohort naïve to DENV and ZIKV was used (n=8). The immunological status was determined by IgG, IgM, NS1 ELISA and neutralization assays. All cohorts were exposed to ZIKV (H/PF 2013) and viremia was followed for 1-10, 15 & 30 days post infection (dpi), we also looked for virus on urine and saliva up to 30 dpi by qRTPCR. Neutralizations to ZIKV and DENV before infection and after 30dpi were determined by PRNT/FRNT (50 or 60). Most of the DENV pre-exposed cohorts showed cross-reactivity to ZIKV envelope. Only DENV2 pre-exposed, recognized ZIKV NS1 protein. Before ZIKV challenge, pre exposed cohorts cross-neutralized all other serotypes but failed to neutralize ZIKV. 30 days after ZIKV challenge, pre-exposed cohorts neutralized ZIKV and also neutralization titers against all 4 DENV serotypes increased. Naïve cohort strongly neutralized ZIKA and only ¼ animals poorly neutralized DENV. Viremia length and viral load was similar in pre exposed cohorts and naïve cohort, suggesting the absence of ADE in vivoafter secondary ZIKV infection. No virus was detected in saliva and intermittent viruria was observed. Our data shows cross reactivity between DENV and ZIKV in acute and convalescent samples from NHP infected with DENV but with very limited or lack of cross-neutralizing activity against ZIKV. Also we found no evidence of in vivo ADE, as viral loads were similar for all samples tested. These results are in agreement with data observed in humans, showing that Zika naïve subjects have low or none neutralizing antibodies to other flavivirus including DENV.