Zika virus (ZIKV) is an arbovirus primarily transmitted by Aedes mosquitoes. Like most viral infections, ZIKV viremia varies over several orders of magnitude, with unknown consequences for transmission. To determine the effect of viral concentration on ZIKV transmission risk, we exposed field-derived Ae. aegypti mosquitoes to four doses (103, 104, 105, 106 PFU/mL) representative of potential variation in the field. We demonstrate that increasing ZIKV dose in the blood-meal significantly increases the probability of mosquitoes becoming infected, and consequently disseminating virus and becoming infectious. Additionally, we observed significant interactions between dose and days post-infection on dissemination and overall transmission efficiency, suggesting that variation in ZIKV dose affects the rates of midgut escape and salivary gland invasion. We did not find significant effects of dose on mosquito mortality. We also demonstrate that detecting virus using RT-qPCR approaches rather than plaque assays potentially over-estimates key transmission parameters, including the time at which mosquitoes become infectious and viral burden. Finally, using these data to parameterize an R0 model, we showed that increasing viremia from 104 to 106 PFU/mL increased relative R0 3.8-fold, demonstrating that variation in viremia substantially affects transmission risk.

Zika virus (ZIKV) is an arbovirus primarily transmitted by Aedes mosquitoes. Like most viral infections, ZIKV viremia varies over several orders of magnitude, with unknown consequences for transmission. To determine the effect of viral concentration on ZIKV transmission risk, we exposed field-derived Ae. aegypti mosquitoes to four doses (10 3 , 10 4 , 10 5 , 10 6 PFU/mL) representative of potential variation in the field. We demonstrate that increasing ZIKV dose in the blood-meal significantly increases the probability of mosquitoes becoming infected and infectious, as well as the rate at which virus spreads to the saliva, but found no effect on dissemination efficiency or mosquito mortality. We also demonstrate that determining infection using RT-qPCR approaches rather than plaque assays potentially over-estimates key pathogen parameters, including the time at which mosquitoes become infectious and viral burden. Finally, using these data to parameterize an R 0 model, we demonstrate that variation in viremia substantially affects transmission risk. Keywords:Zika virus, viremia, Ae. aegypti, transmission, R 0All rights reserved. No reuse allowed without permission.(which was not peer-reviewed) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.The copyright holder for this preprint . http://dx.doi.org/10.1101/221572 doi: bioRxiv preprint first posted online Nov. 17, 2017; 3 IntroductionAlthough discovered in 1947 (1), Zika virus (ZIKV) has recently become a public health concern due to its rapid spread and newly identified teratogenic effects. Shortly after isolation from a rhesus macaque in Uganda, the virus caused several mild infections in humans (2, 3).ZIKV infections remained unapparent until the first major outbreak in 2007 on the island of Yap (4). The virus further spread across the Pacific, where it was first associated with Guillain-Barré syndrome during the 2014 French Polynesian outbreak (5). In 2015, transmission was confirmed in Brazil (6), after which the virus spread rapidly across the Americas (7). ZIKV was declared a "public health emergency of international concern" by WHO in 2016 due to excessive spread and increases in complications associated with congenital Zika virus syndrome (8).The primary route of ZIKV transmission is through the bite of Aedes mosquitoes. The principal urban vector in the Americas is Ae. aegypti while Ae. albopictus is believed to be a secondary vector (9). Although most cases of ZIKV infection are asymptomatic (4), 20% of individuals develop symptoms associated with Zika fever (10). Currently, human viremia is not well characterized. Studies suggest that ZIKV viremia in the blood is lower than other arboviruses and does not significantly differ between symptomatic and asymptomatic patients (11). In arboviral systems such as dengue, variation in viremia across infectious human hosts influence the number of mosquitoes that become infectious (12), yet this has only been minimally explored in the ZIKV system (13-15). Fu...