Sudeep A B, Mandar Paingankar, Ghodke Y K, George R P, Gokhale M D
National Institute of Virology (ICMR), Pune, India.
J Vector Borne Dis. 2015 Sep;52(3):185-92.
BACKGROUND & OBJECTIVES: Culex quinquefasciatus is one of the principal vectors of West Nile virus (WNV). The mosquito also acts as a bridge vector as it feeds on both birds and humans. In the background of the recent reports of WNV activity in Kerala and Assam with fatalities, a study was initiated to determine the growth kinetics and transmission mechanisms of three strains of WNV in two populations of Cx. quinquefasciatus.
Mosquitoes were infected by oral feeding and growth on different post-infection days was determined with the three strains. Horizontal transmission was determined by confirming sickness and mortality in infant mice after infected mosquito bite. F1 generation eggs, larvae, pupae and adults of experimentally infected mosquitoes were screened for WNV to determine vertical (transovarial) transmission. Trans-stadial transmission was determined by detecting WNV in adult mosquitoes emerged from infected larvae.
Both the mosquito populations replicated and maintained WNV for a prolonged period with high titers (≥ 5log10 PFU/ml). WNV could be detected in saliva from Days 2 to 32 post-infection. Horizontal transmission by both the populations could be established but no vertical transmission was observed. However, parenterally infected larvae transmitted WNV to adults.
INTERPRETATION & CONCLUSION: WNV has been isolated from >10 mosquito species from India, however, vector competence of none of the species has been studied. The present study demonstrates efficient transmission of WNV by Cx. quinquefasciatus mosquitoes. With its country wide prevalence and high vector competence, the mosquitoes could create grave consequences especially when virulent strains with potential to cause acute flaccid paralysis and death are circulating.
致倦库蚊是西尼罗河病毒（WNV）的主要传播媒介之一。这种蚊子以鸟类和人类为食，还充当桥梁媒介。鉴于近期喀拉拉邦和阿萨姆邦有西尼罗河病毒活动并出现死亡病例的报道，开展了一项研究，以确定三株西尼罗河病毒在致倦库蚊两个种群中的生长动力学和传播机制。
通过经口喂食使蚊子感染病毒，并测定这三株病毒在感染后不同天数的生长情况。通过确认受感染蚊子叮咬后幼鼠的发病和死亡情况来确定水平传播。对实验感染蚊子的F1代卵、幼虫、蛹和成虫进行西尼罗河病毒筛查，以确定垂直（经卵）传播。通过检测从受感染幼虫羽化出的成年蚊子中的西尼罗河病毒来确定跨龄期传播。
两个蚊子种群都能长时间复制并维持高滴度（≥5log10 PFU/ml）的西尼罗河病毒。在感染后第2天至第32天的唾液中可检测到西尼罗河病毒。两个种群都能实现水平传播，但未观察到垂直传播。然而，经肠道外感染的幼虫可将西尼罗河病毒传播给成虫。
在印度已从超过10种蚊子中分离出西尼罗河病毒，但尚未对任何一种蚊子的媒介能力进行研究。本研究证明致倦库蚊能有效传播西尼罗河病毒。鉴于这种蚊子在全国范围内普遍存在且媒介能力强，尤其是当有导致急性弛缓性麻痹和死亡的毒株传播时，可能会造成严重后果。
