These four female Culex mosquitoes have clearly fed on the honey-baited FTA card as evidenced by the visible blue honey in their abdomens. (Photo: Nadja Wipf).

Collecting mosquito saliva on FTA cards

The idea to take advantage of the fact that infectious mosquitoes spit out viruses in their saliva not only during blood- but also duringsugar-feedingis not new.Australian researchers, who dared to think out of the box, came up with the idea to collect mosquito saliva on honey-soaked filter papers housed in mosquito traps. They did not just use any filter paper but special ones coated with a patented mix of chemicals that inactivate pathogens and preserve DNA and RNA at ambient temperature, so calledFlinders Technology Associates（FTA^®) filter paper cards. The presence or absence of viruses can later be detected in the lab with molecular methods (e.g. withpolymerase chain reactionsspecifically targeting the viral genome). With this innovative technique, they could overcome the limitations of laborious and cold chain dependent screening of thousands of mosquitoes.

Why is it important to detect viruses in mosquitoes?

欧洲大陆的蚊子传播病毒的威胁正在增加chikungunya,dengue和西尼罗病毒outbreaks. In Switzerland, despite the presence of competent vectors, regular reports of human cases and local transmissions of mosquito-borne viral diseases in neighbouring countries, there is still no routine surveillance system in place to detect circulating viruses in mosquitoes.在瑞士南部的现场试验中, we evaluated which mosquito traps work best in combination with FTA cards. We also assessed the sensitivity of the honey-bait approach by testing both the collected mosquitoes and the FTA cards for the presence of viruses.

我们是如何捕获蚊子的？

In our field trial we compared three commercially available mosquito traps:

• The BG-Sentinel 2 trap actively catches host-seeking mosquitoes by sucking them into a collection bag with a battery driven fan. This trap emits CO₂和人造气味，模仿了吸引蚊子自然宿主的提示。
• BG-GAT陷阱被干草输注诱饵，最好将其描述为含有有机碎片的臭水，妊娠雌性蚊子似乎发现产卵特别有吸引力。这是我们在我们的研究中使用的最简单，最便宜的陷阱不需要任何电力。
• The Box gravid trap consists of what looks like a grey toolbox placed across a black pan filled with hay infusion. The toolbox contains a battery driven fan that sucks mosquitoes, which are approaching the water surface, into the collection chamber.

We set the three types of mosquito traps in urban and suburban areas of southern Switzerland. One trapping session lasted 48 hours and each trap was set 80 times between July and October 2016.

Which mosquito trap worked best?

In our study, the Box gravid trap caught by far the most mosquitoes – in fact over 11 times more – than the other trap types. Besides being the most efficient trap and catching the broadest variety ofCulex和Aedes物种，我个人发现它是与蜂蜜诱饵FTA卡结合使用的最方便的陷阱。其收集室的内壁非常适合固定卡片，因为它受到环境影响，并易于被捕获的蚊子易于接近。

我们怎么知道蚊子在FTA卡上喂了？

因为我们将蜂蜜用蓝色食物染料染色 - 我们知道如果在立体声显微镜下检查它们时，如果我们在其体内检测到它们的蓝色，是否在FTA卡上喂了蚊子。平均三分之三的四个被捕获在蜂蜜诱饵上的蚊子，我们认为这是令人满意的喂养率。

Did we detect mosquito-borne viruses?

是的!最令人兴奋的结果本研究that we detectedUsutu病毒在六个池中Culex蚊子es and also on the FTA card placed in the same Box gravid trap that caught these infected mosquitoes. Remarkably, we only saw blue honey in two of theseCulex蚊子es. This suggests, that we detected Usutu virus from saliva of as little as one or two infectious mosquitoes on the FTA card, emphasising the high sensitivity of this method.

基于令人鼓舞的结果，我们在瑞士南部不断使用蜂蜜诱饵的FTA卡来监视蚊子传播病毒。此外，其他瑞士地区也表示有兴趣使用FTA卡方法来监视目的。