A Zika virus mutation that associates with fetal death in rhesus macaques reduces transmission by Aedes aegypti mosquitoes
Lemos DECV1 Grubaugh ND2, Singapuri A1, Tsetsarkin K3, Van Rompay KK4, Chiu CY5, Andersen KG3, Coffey LL1* 1University of California, Davis, School of Veterinary Medicine 2The Scripps Research Institute 3National Institute of Allergy and Infectious Diseases 4University of California, Davis, California National Primate Research Center 5University of California, San Francisco, School of Medicine
Fetal microcephaly and death are now recognized as severe forms of congenital Zika syndrome; however, it is still unclear whether recent Zika virus (ZIKV) mutations contribute to this phenotype. We identified a single intra-host variant in the ZIKV NS2B protein (NS2BM1404I) from a rhesus macaque (RM) fetus that died after experimental ZIKV inoculation in the first trimester. Targeted deep sequencing flanking NS2B1404 in subsequent cohorts of RM mothers and their fetuses identified NS2BM1404I at minority frequency and sometimes at consensus levels in 100% (7/7) of dead or stillborn RM fetuses and/or the plasma of their mothers and in 26% (4/15) of RM mother and fetus pairs whose fetuses survived to near term or were born alive. By examining sequence data from recent epidemics, we found that NS2BM1404I occurs rarely (5/500, 1%) in consensus human ZIKV genomes. We also deep sequenced ZIKV genomes from non-pregnant humans adults, infants, and Ae. aegypti from the epidemic and observed that NS2BI1404 was more often present at intra-host levels in humans compared to mosquitoes. Since the primary ZIKV transmission cycle is human-mosquito-human, viral mutations that arise in one host must be maintained in the alternate host to be perpetuated. We therefore hypothesized that ZIKV NS2BM1404I may not be efficiently transmitted by Aedes aegypti mosquitoes, explaining its low frequency in humans during outbreaks. We engineered NS2BM1404I into a ZIKV infectious clone and examined vector competence in Ae. aegypti from Puerto Rico. Although infection and dissemination rates were not different, we found that Ae. aegypti did not transmit ZIKV-NS2BI1404 as efficiently compared to ZIKV-NS2BM1404 7 [3/20 (15%) versus 13/20 (65%), P<0.001, Chi-squared] days post-feed. The poor transmissibility of this potentially human/primate adaptive ZIKV mutation identified here may explain its low frequency in febrile humans. Furthermore, our data highlights the evolutionary complexity during arbovirus transmission cycles and suggests that some pathogenic mutations are not likely to spread in epidemics.
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