ICMR-National Institute of Virology, Pune, India.
Medical Entomology Group; ICMR-National Institute of Virology, Pune, India.
Indian J Med Res. 2018 Jan;147(1):88-96. doi: 10.4103/ijmr.IJMR_1142_17.
BACKGROUND & OBJECTIVES: There are reports about the susceptibility of Aedes mosquitoes to ZIKV from various countries, however, no such information is available from Indian sub-continent, although, high level of group cross-reactivity of ZIKV with other flaviviruses has been reported. During outbreak situations, many cases of Dengue (DEN) and Chikungunya (CHIK) are reported. In such scenario, vector mosquitoes are likely to get co-infection/secondary-infection with one or other virus. The present study was carried out to determine the susceptibility of Indian strain of Aedes aegypti to Zika virus (ZIKV) strain (MR-766) and the effect of co-infection/super-infection with either dengue virus (serotype-2) (DENV) or chikungunya virus (CHIKV) on ZIKV replication.
Ae. aegypti mosquitoes used in this study were reared for many generations since 1980 at laboratory colony maintained at the ICMR-National Institute of Virology, Pune, India. Transmissibility of ZIKV from infected mosquitoes to suckling mice was also studied. Mosquitoes were experimentally infected with ZIKV and super-infected with either DENV or CHIKV via membrane-feeding route and incubated for 14 days at 28±2°C and humidity of 85±5 per cent. Replication of these viruses in mosquitoes was confirmed using real-time reverse transcription-polymerase chain reaction and immunofluorescence assay. Twenty infected mosquitoes were allowed to feed upon four suckling CD1 mice for about 30 min. Transmission of the ZIKV by infected mosquitoes to suckling mice was confirmed by the appearance of clinical signs and the presence of viral RNA in different organs.
Concomitant infection of mosquitoes with all the three viruses showed simultaneous propagation of all three viruses, confirmed by real time RT-PCR and IFA. Infection of mosquitoes with CHIKV followed by ZIKV showed positivity in individual head squashes (7%) for both viruses using IFA; only 8.3 per cent showed dual positivity with primary infection of ZIKV followed by DENV; 8.3 per cent dual infection positivity was observed when infected with DENV followed by ZIKV; 5 per cent showed dual infection was observed when infected with ZIKV followed by CHIKV. Ae. aegypti was found to be susceptible to ZIKV strain as ZIKV could be detected from the second post-infection day (PID) in infected mosquitoes. Transmission of ZIKV to mice by the bite of infected Ae. aegypti establishes this species as a potential vector.
INTERPRETATION & CONCLUSIONS: From super-infection experiments, it was concluded that ZIKV might have a relative advantage in replication dynamics over DENV. Vertical transmission was not observed for ZIKV in experimentally infected mosquitoes (n=920 larvae). Further studies are required to understand the possibility of silently circulating ZIKV in India, which remain non-detected because of lack of surveillance.
已有来自不同国家的关于伊蚊对寨卡病毒易感性的报告，但来自印度次大陆的此类信息尚不可用，尽管已报道寨卡病毒与其他黄病毒之间存在高水平的群体交叉反应性。在疫情爆发期间，经常有登革热（DEN）和基孔肯雅热（CHIK）的病例报告。在这种情况下，病媒蚊子很可能会同时感染/继发感染一种或另一种病毒。本研究旨在确定印度白纹伊蚊对寨卡病毒（ZIKV）株（MR-766）的易感性，以及与登革热病毒（血清型 2）（DENV）或基孔肯雅热病毒（CHIKV）共同感染/继发感染对 ZIKV 复制的影响。
本研究中使用的埃及伊蚊自 1980 年以来在印度浦那 ICMR-国家病毒学研究所的实验室群体中进行了多代饲养。还研究了从感染蚊子向乳鼠传播寨卡病毒的情况。通过膜喂养途径，用 ZIKV 对蚊子进行实验感染，并再次感染 DENV 或 CHIKV，在 28±2°C 和 85±5%的湿度下孵育 14 天。使用实时逆转录聚合酶链反应和免疫荧光测定法确认这些病毒在蚊子中的复制。让 20 只感染的蚊子吸食 4 只乳鼠约 30 分钟。通过感染蚊子向乳鼠传播的临床症状和不同器官中病毒 RNA 的存在来确认寨卡病毒的传播。
三种病毒的同时感染显示出三种病毒的同时传播，通过实时 RT-PCR 和 IFA 得到证实。用 IFA 对 CHIKV 感染的蚊子进行后续 ZIKV 感染，在个别头部涂片（7%）中均呈阳性；仅 8.3%的初次感染 ZIKV 后感染 DENV 呈双阳性；8.3%的双感染阳性见于初次感染 DENV 后感染 ZIKV；5%的双感染阳性见于初次感染 CHIKV 后感染 ZIKV。白纹伊蚊被发现易感染寨卡病毒，因为可以从感染后的第二天（2 日龄）在感染的蚊子中检测到寨卡病毒。受感染的埃及伊蚊叮咬将寨卡病毒传播给小鼠，这表明该物种可能是一种潜在的传播媒介。
从超级感染实验得出结论，寨卡病毒在复制动力学方面可能相对于 DENV 具有相对优势。在实验感染的蚊子（n=920 只幼虫）中未观察到寨卡病毒的垂直传播。需要进一步研究以了解寨卡病毒在印度境内可能存在但未被发现的情况，这是因为缺乏监测而导致的。
