Vector competence of Aedes albopictus and Aedes aegypti from the islands of the Southwestern Indian Ocean for epidemic Zika, dengue, and chikungunya viruses

Abstract

Background: Aedes albopictus and Aedes aegypti are key vectors involved in the transmission of human pathogens worldwide. Epidemiological studies have demonstrated varying levels of arbovirus transmission by these mosquito vectors, leading to an increasing number of investigations that assess vector competence (the ability of an insect to become infected and subsequently transmit a pathogen) of Ae. albopictus and Ae. aegypti lines, to decipher the risks associated with each species. In this study, we evaluated the vector competence of Ae. albopictus and Ae. aegypti lines from the Southwestern Indian Ocean (SWIO) for three arboviruses: Zika virus (ZIKV), dengue virus serotype-1 (DENV-1), and chikungunya virus (CHIKV).

Methods: Ten mosquito lines (eight Ae. albopictus and two Ae. aegypti lines), collected from five islands within SWIO (the Seychelles, the Comoros, and the Mascarene archipelagoes), were exposed to epidemic strains of ZIKV, DENV-1, and CHIKV. Three vector competence parameters (infection rate [IR], dissemination efficiency [DE], and transmission efficiency [TE]) were assessed at different days post exposure (dpe) to infectious blood meals, using plaque forming unit (PFU) assays. In addition, viral loads were quantified in positive saliva. These parameters were then compared between mosquito lines, geographic origins, and dpe for each virus.

Results: None of the mosquito lines were competent for the ZIKV strain tested. In contrast, both Ae. albopictus and Ae. aegypti lines were competent vectors for the strains of DENV-1 and CHIKV tested, with transmission efficiencies reaching 35.4% for DENV-1 and 62.5% for CHIKV. For both mosquito species, statistical analyses revealed that dpe significantly influenced vector competence parameters, whereas the geographic origin of mosquito lines did not.

Conclusions: The observed vector competence patterns for the three tested viruses might partly explain their current epidemiology in the SWIO. This approach should involve a larger number of Ae. aegypti lines and should be extended to other ZIKV, DENV, and CHIKV strains, as well as to viruses not currently reported in the region, to better assess the risk of (re-)emergence of mosquito-borne viruses in the SWIO.

Keywords: Aedes aegypti; Aedes albopictus; Arboviruses; Islands of the Southwestern Indian Ocean; Transmission risk; Vector competence.

Fig. 1

Maps showing collection sites of Aedes albopictus and Aedes aegypti mosquitoes in the SWIO. A Localization of surveyed islands in the SWIO. Sampling sites in the (B) Comoros archipelago, C Seychelles archipelago, and (D) Mascarene archipelago. Blue and red points indicate sites where Ae. albopictus and Ae. aegypti mosquitoes, respectively, were collected to establish laboratory colonies

Fig. 2

Virus testing schedule across days post exposure (dpe) for each mosquito line. Rows represent mosquito lines, columns correspond to time points (7, 14, 21, and 28 dpe), and colored squares denote tested viruses: ZIKV (red), DENV-1 (green), and CHIKV (blue)

Fig. 3

Vector competence parameters of Aedes albopictus and Aedes aegypti lines exposed to the ZIKV strain. Graphics A–C correspond to infection rate (IR), dissemination efficiency (DE), and transmission efficiency (TE), respectively. Mosquito lines were tested at 7, 14, and 21 days post exposure (dpe) to the ZIKV. Samples were examined for the presence of infectious viral particles by plaque forming unit (PFU) titration on Vero cells: bodies for the IR, heads for the DE, and saliva for the TE. Error bars correspond to the 95% confidence interval. COM Comoros archipelago, SEY Seychelles archipelago, RUN Reunion Island, N, number of mosquitoes tested, NA not available

Fig. 4

Vector competence parameters of Aedes albopictus and Aedes aegypti lines exposed to the DENV-1 strain. Graphics (A–C) correspond to infection rate (IR), dissemination efficiency (DE), and transmission efficiency (TE), respectively. Mosquito lines were tested at 14, 21, and 28 days post exposure (dpe) to DENV-1. Samples were examined for infectious viral particles plaque forming unit (PFU) titration on Vero cells: in the bodies for the IR, the heads for DE, and the saliva for TE. Error bars represent 95% confidence intervals. COM Comoros archipelago, SEY Seychelles archipelago, RUN Reunion Island, N number of mosquitoes tested, NA not available

Fig. 5

Vector competence parameters of Aedes albopictus and Aedes aegypti lines exposed to the CHIKV strain. Graphics (A–C) correspond to infection rate (IR), dissemination efficiency (DE), and transmission efficiency (TE), respectively. Mosquito lines were tested at 7 and 14 days post exposure (dpe) with the CHIKV. Samples were examined for the presence of infectious viral particles by plaque forming unit (PFU) titration on Vero cells: in the bodies for the IR, head for the DE, and saliva for the TE. Error bars correspond to the 95% confidence interval. COM Comoros archipelago, SEY Seychelles archipelago, RUN Reunion Island, N number of mosquitoes tested, NA not available