Ovitraps are now being marketed by the DOST. UP Manila students set-up a drive to collect empty cans that can be used to build ovitraps for our rural community partner. But does it really work?

First, let's tackle what ovitraps are. Ovitraps are primarily surveillance tools researches use to determine the number of breeding mosquitos in the area. It is made of a small container partially filled with water and a strip which serves as the site for egg-laying. During my undergrad, we used it to catch our mosquitos for our entomology project. So, if you just want to catch mosquitos. Yes, it works.

Ovitrap yo!

Now, some people thought that maybe instead of just for surveillance we can use it to kill those pesky mosquitos in our area. So they made a lethal version of the ovitrap by adding instecticides such as bifenthrin. They call this the lethal ovitrap. Basically, it attracts gravid mosquitos to use the can. When a mosquito touches the strip, it comes in contact with the insecticide. Thus, whether it decides to lay eggs there or somewhere else, it will die. Gravid mosquitos die, less mosquitos in the area, less mosquitos, less likely to be bitten and less dengue cases. Like most innovations, it sounds good on paper. But again, do we reach our end objective of less dengue cases?

If you aim to just decrease the mosquito population, it does work. As Australia, Thailand, Brazil, Mexico and Venenzuela would tell you. An Australian laboratory study showed that lethal ovitraps were less attractive to mosquitos for egg laying but still works because only contact is needed to kill mosquitos. Field studies (links above) showed that lethal ovitraps deployed for around four weeks were able to continually capture and kill mosquitos and decrease vector indices in the area. Ovitraps are effective in decreasing adult mosquito populations.

Sounds good, right? So, should we start deploying these traps? Or as what DOST is doing, marketing these things as a primary tool for ending this apparent dengue epidemic? (Assuming that this is a real epidemic.)


My answer is no. We still do not know how this decrease in mosquito numbers affect the number of infected mosquitos, the number of bites people receive, the number of people getting bitten and the number of getting infected in the area. Again, the most important thing for dengue prevention is to not get bitten by infected mosquitos. It would not surprise me if reducing numbers of mosquitos would have little effect on the number of cases. I really hate it how public health programs are rolled out with inadequate evidence base. What's the effect on dengue incidence dammit?!

But it's will be very easy to convince me. Just show in a community trial that the number of dengue cases decreased in that area. And it wouldn't take too long, as this is acute disease were are taking about a 1 to 2 month trial would suffice. Apparently, they already conducted field trials to test the effectiveness of these ovitraps in decreasing mosquito populations in urban settings such as Marikina and Quezon City. True to Philippine tradition, we only have a press release available. I hope they also collected dengue surveillance data. Better, if they conducted sero-conversion surveys but I doubt if they have the funding for that.
And what's more frustrating is that I know that I'm not the only person in this country that knows what DOST is doing is wrong. But why aren't those more strategically located individuals pointing out that we need that study?