Zika Virus, a New Threat for Europe?

Abstract

Background: Since its emergence in 2007 in Micronesia and Polynesia, the arthropod-borne flavivirus Zika virus (ZIKV) has spread in the Americas and the Caribbean, following first detection in Brazil in May 2015. The risk of ZIKV emergence in Europe increases as imported cases are repeatedly reported. Together with chikungunya virus (CHIKV) and dengue virus (DENV), ZIKV is transmitted by Aedes mosquitoes. Any countries where these mosquitoes are present could be potential sites for future ZIKV outbreak. We assessed the vector competence of European Aedes mosquitoes (Aedes aegypti and Aedes albopictus) for the currently circulating Asian genotype of ZIKV.

Methodology/principal findings: Two populations of Ae. aegypti from the island of Madeira (Funchal and Paul do Mar) and two populations of Ae. albopictus from France (Nice and Bar-sur-Loup) were challenged with an Asian genotype of ZIKV isolated from a patient in April 2014 in New Caledonia. Fully engorged mosquitoes were then maintained in insectary conditions (28°±1°C, 16h:8h light:dark cycle and 80% humidity). 16-24 mosquitoes from each population were examined at 3, 6, 9 and 14 days post-infection to estimate the infection rate, disseminated infection rate and transmission efficiency. Based on these experimental infections, we demonstrated that Ae. albopictus from France were not very susceptible to ZIKV.

Conclusions/significance: In combination with the restricted distribution of European Ae. albopictus, our results on vector competence corroborate the low risk for ZIKV to expand into most parts of Europe with the possible exception of the warmest regions bordering the Mediterranean coastline.

Fig 1

Ae. aegypti from Madeira Island and Ae. albopictus from France were assessed for viral infection (A, B), dissemination (C, D), and transmission (E, F) at days 3, 6, 9, 14 after infection with ZIKV provided at a titer of 10⁷ TCID₅₀/mL. 16–24 mosquitoes were sampled each day. Infection rates were measured as the percentage of mosquitoes with infected bodies among the total number of analyzed mosquitoes. Disseminated infection rates were estimated as the percentage of mosquitoes with infected heads (i.e., the virus has successfully crossed the midgut barrier to reach the hemocoel) among the total number of mosquitoes with infected bodies. The transmission efficiency was calculated as the overall proportion of females with infectious saliva among the total number of tested mosquitoes. AE = Ae. aegypti; AL = Ae. albopictus. In red, countries where ZIKV has been isolated. Error bars show the confidence intervals (95%). In brackets, the number of mosquitoes tested.

Fig 2

Viral loads in heads (A) and saliva (B) for mosquitoes infected with ZIKV provided at a titer of 10⁷ TCID₅₀/mL. The number of infectious particles per head homogenate and saliva was estimated by plaque assays on Vero cells. Titers were expressed as PFU (plaque-forming unit). AE = Ae. aegypti; AL = Ae. albopictus. Error bars refer to the standard error. In brackets, the number of mosquitoes tested.