Zika virus outbreak in the Pacific: Vector competence of regional vectors

International audienceBackgroundIn 2013, Zika virus (ZIKV) emerged in French Polynesia and spread through the Pacific region between 2013 and 2017. Several potential Aedes mosquitoes may have contributed to the ZIKV transmission including Aedes aegypti, the main arbovirus vector in the region, and Aedes polynesiensis, vector of lymphatic filariasis and secondary vector of dengue virus. The aim of this study was to analyze the ability of these two Pacific vectors to transmit ZIKV at a regional scale, through the evaluation and comparison of the vector competence of wild Ae. aegypti and Ae. polynesiensis populations from different Pacific islands for a ZIKV strain which circulated in this region during the 2013–2017 outbreak.Methodology/principal findingsField Ae. aegypti (three populations) and Ae. polynesiensis (two populations) from the Pacific region were collected for this study. Female mosquitoes were orally exposed to ZIKV (107 TCID50/mL) isolated in the region in 2014. At 6, 9, 14 and 21 days post-infection, mosquito bodies (thorax and abdomen), heads and saliva were analyzed to measure infection, dissemination, transmission rates and transmission efficiency, respectively. According to our results, ZIKV infection rates were heterogeneous between the Ae. aegypti populations, but the dissemination rates were moderate and more homogenous between these populations. For Ae. polynesiensis, infection rates were less heterogeneous between the two populations tested. The transmission rate and efficiency results revealed a low vector competence for ZIKV of the different Aedes vector populations under study.Conclusion/significanceOur results indicated a low ZIKV transmission by Ae. aegypti and Ae. polynesiensis tested from the Pacific region. These results were unexpected and suggest the importance of other factors especially the vector density, the mosquito lifespan or the large immunologically naive fraction of the population that may have contributed to the rapid spread of the ZIKV in the Pacific region during the 2013–2017 outbreak.Author summaryZika virus (ZIKV) was isolated for the first time in Uganda in 1947. The virus was sporadically detected in Africa and Asia during few decades. The first human outbreak was declared in Yap Island in Micronesia in 2007. The virus reemerged in 2013 in French Polynesia and circulated throughout the Pacific region and in Americas between 2013 and 2017. ZIKV is transmitted to human by the bite of an infected mosquito. Aedes mosquitoes were particularly incriminated in the ZIKV outbreak. In this study, we showed for the first time the results of vector competence study of wild Aedes aegypti and Aedes polynesiensis from different islands of the Pacific region. Our results demonstrated an unexpected homogenous and low ZIKV vector competence for the different populations of these two vectors. These findings seemed to indicate that other factors have contributed to the rapid spread of ZIKV in the Pacific region