Nasar Farooq, Haddow Andrew D, Tesh Robert B, Weaver Scott C
Institute for Human Infections and Immunity, Center for Tropical Diseases, and Department of Pathology, University of Texas Medical Branch, Galveston, TX, 77555, USA.
Present Address: Virology Division, United States Army Medical Research Institute of Infectious Diseases, 1425 Porter Street, Frederick, MD, 21702, USA.
Parasit Vectors. 2014 Dec 17;7:595. doi: 10.1186/s13071-014-0595-2.
Most alphaviruses are arthropod-borne and utilize mosquitoes as vectors for transmission to susceptible vertebrate hosts. This ability to infect both mosquitoes and vertebrates is essential for maintenance of most alphaviruses in nature. A recently characterized alphavirus, Eilat virus (EILV), isolated from a pool of Anopheles coustani s.I. is unable to replicate in vertebrate cell lines. The EILV host range restriction occurs at both attachment/entry as well as genomic RNA replication levels. Here we investigated the mosquito vector range of EILV in species encompassing three genera that are responsible for maintenance of other alphaviruses in nature.
Susceptibility studies were performed in four mosquito species: Aedes albopictus, A. aegypti, Anopheles gambiae, and Culex quinquefasciatus via intrathoracic and oral routes utilizing EILV and EILV expressing red fluorescent protein (-eRFP) clones. EILV-eRFP was injected at 10(7) PFU/mL to visualize replication in various mosquito organs at 7 days post-infection. Mosquitoes were also injected with EILV at 10(4)-10(1) PFU/mosquito and virus replication was measured via plaque assays at day 7 post-infection. Lastly, mosquitoes were provided bloodmeals containing EILV-eRFP at doses of 10(9), 10(7), 10(5) PFU/mL, and infection and dissemination rates were determined at 14 days post-infection.
All four species were susceptible via the intrathoracic route; however, replication was 10-100 fold less than typical for most alphaviruses, and infection was limited to midgut-associated muscle tissue and salivary glands. A. albopictus was refractory to oral infection, while A. gambiae and C. quinquefasciatus were susceptible only at 10(9) PFU/mL dose. In contrast, A. aegypti was susceptible at both 10(9) and 10(7) PFU/mL doses, with body infection rates of 78% and 63%, and dissemination rates of 26% and 8%, respectively.
The exclusion of vertebrates in its maintenance cycle may have facilitated the adaptation of EILV to a single mosquito host. As a consequence, EILV displays a narrow vector range in mosquito species responsible for the maintenance of other alphaviruses in nature.
大多数甲病毒是节肢动物传播的，利用蚊子作为传播媒介将病毒传播给易感脊椎动物宿主。这种感染蚊子和脊椎动物的能力对于自然界中大多数甲病毒的维持至关重要。最近鉴定出的一种甲病毒，埃拉特病毒（EILV），从一群库斯塔尼按蚊（Anopheles coustani s.I.）中分离得到，它无法在脊椎动物细胞系中复制。EILV的宿主范围限制发生在附着/进入以及基因组RNA复制水平。在此，我们研究了EILV在包含自然界中负责维持其他甲病毒的三个属的蚊子物种中的传播媒介范围。
通过胸腔内注射和口服途径，利用EILV和表达红色荧光蛋白的EILV（-eRFP）克隆，对四种蚊子进行易感性研究，这四种蚊子分别是白纹伊蚊（Aedes albopictus）、埃及伊蚊（A. aegypti）、冈比亚按蚊（Anopheles gambiae）和致倦库蚊（Culex quinquefasciatus）。以10⁷ PFU/mL的剂量注射EILV-eRFP，以观察感染后7天在各种蚊子器官中的复制情况。还以10⁴ - 10¹ PFU/蚊子的剂量给蚊子注射EILV，并在感染后第7天通过蚀斑试验测量病毒复制情况。最后，给蚊子提供含有剂量为10⁹、10⁷、10⁵ PFU/mL的EILV-eRFP的血餐，并在感染后14天确定感染率和传播率。
所有四种蚊子通过胸腔内注射途径均易感；然而，其复制水平比大多数甲病毒的典型复制水平低10 - 100倍，并且感染仅限于中肠相关肌肉组织和唾液腺。白纹伊蚊对口服感染具有抗性，而冈比亚按蚊和致倦库蚊仅在10⁹ PFU/mL的剂量下易感。相比之下，埃及伊蚊在10⁹和10⁷ PFU/mL的剂量下均易感，体内感染率分别为78%和63%，传播率分别为26%和8%。
在其维持循环中排除脊椎动物可能促进了EILV对单一蚊子宿主的适应。因此，EILV在自然界中负责维持其他甲病毒的蚊子物种中的传播媒介范围较窄。
