Day 5: Catching Those Pesky Mosquitoes

Thursday 12 Aug

Thursday started early. We planned to head out to Madera to collect the traps at 6:30, and I was excited. I waited on the porch of our lodging, taking in the eastern African sky. We’re about on the equator here, so 6:30 is that point in the sunrise just after silhouette time (my favorite) when that skyline gradient is the most saturated. A great time for an energy bar and some good morning thinking.

The children in these villages think I’m hilarious – just the sight of me makes them laugh. While collecting our traps, which unfortunately were not very full due to rains during the night, we were often accompanied by groups of children just watching and laughing. I won’t disagree, I am funny looking, especially in my current hair state! I really enjoyed the attention, which anyone who knows me will find unsurprising.

The traps left us dissatisfied, so we tried another method of capture called Pyrethrum Spray Catch or PSC (I hope you’re keeping notes on these acronyms). This is fascinating: When female mosquitos take their blood meal at night, they often will find a place to rest, digest, and grow their eggs. Even if they don’t get the chance to feed, many mosquitos will try to rest in the early morning. In a hut, the best place is on the inside of the roof. PSC takes advantage of this behavior by turning the hut into a giant trap. The VCOs and VHTs place white sheets on the ground in the hut, covering the entire floor. Then one person takes a can of aerosol insecticide, walks inside the hut, and closes the door. Their partner takes another can and stands just outside. They coordinate through the door to each travel the circumference of the hut in opposite directions, and then the caps come off. The outside person then squat-run-sprays around the hut perimeter, ensuring they cover the eaves and any other possible escape for the mosquitos. Meanwhile, the inside person fills the entire hut with insecticide until they can no longer breathe, at which point they push their way through the door coughing and squeezing their eyes closed. It’s crazy!

After 7 minutes, all the mosquitos are “knocked down” by the insecticide and the sheets are brought out and laid on the dirt outside. The sheets are kept folded up, because these mosquitos are actually pyrethrum-resistant – the poison only makes them woozy. VCOs (and me!) gather around and the sheet is unfolded section by section, allowing us to pick the mosquitos up by their legs with tweezers (fine, forceps) and drop them into a petri dish. We have to work quickly though, because the wooziness wears off and some mosquitos will fly away if they get the chance. Fun tidbit: pyrethrum also drops other critters – crickets, spiders, spiders, spiders, etc. So we pick through the bugs until we’ve searched the entire sheet, then move on to the next one. It’s actually a pretty fun game!

One other thing about the village – there are animals everywhere. Goats, chickens, ducks, cows, cats, lizards, dogs, pigs, turkeys! They make a real chorus of animal sounds, which I enjoy. Especially the goats, I can’t get enough of those weirdies. It’s very exciting. The Tropical Medicine doctor at home forbade us from touching animals on this trip, which makes me sad, but I still get to listen and watch. There was a tiny blue-eyed calico kitten there that was eating my heart out.

The rains the night prior really wrecked our harvest – bummer! We took our limited yield back to the hotel, where we began the processing. Usually, VCOs take the catch back to their local base where they look at each specimen under microscopy, sort, and count them. In this case, the base was our lodging. If you’re wondering why I keep calling it a lodging, it’s because it’s not a hotel or a motel or a Holiday Inn and don’t know what else to call it, jeez. We briefly considered sorting our insects in the restaurant, then thought better of it and found out there is a giant dance-hall-esque conference room upstairs. Perfect for setting up a mosquito-processing assembly line.

Time to interject with an engineering problem. Earlier in the week, and then again the day before, we had received some critical feedback. Our algorithm was cool and all, yes, species differentiation is very important. But could it tell the user anything about the contents of the mosquito’s belly? Apparently, knowing whether a mosquito has recently fed or whether that blood meal has been partially or fully digested into eggs (abdomen status of semi-gravid or gravid, for my fellow budding entomologists) is a very important element in understanding the mosquito scene. To date, the algo had been entirely trained on images of the mosquito equivalent of raisins, which means it is completely blind to these key parameters. So, in a quick pivot from our original plans for our time in Uganda, Dr. Acharya and I decided to shift our focus to collecting images of fresh and plump mosquitos to re-train the CNN (convolutional neural network).

The rest of the day, and even a bit of the night, we spent trying to image mosquitos. After the VCOs finished their normal identification and tallying we did our work. We used USB microscopes (our imaging gold standard) and phones with clip-on macro lenses. Taking pictures of a bunch of mosquitos doesn’t sound very complicated, but it can be tricky if you’re trying to organize 7 images of each specimen from different cameras on different OSs and map them to Eppendorf tubes later used to PCR the specimens (yep, same PCR as the COVID test, just for genetically differentiating mosquito species). Using our CBID iterative design tricks, we spent most of this time developing a method to efficiently collect and organize these samples. Ultimately we only collected images for ~40 specimens, but we came away with a solid process for the many more images we hoped to collect in the following days.

For the first time on this trip, I got tired. At about 10pm, I really hit a mental wall. Is this the jet lag I was waiting for? I uploaded those images to the cloud for our beautiful Baltimore team to prepare for CNN training and then I hit the hay. Well, not really. I went back to my room and spent some time decompressing while finishing up a musical gift that had been long in the making. It’s amazing that I can lay under a mosquito net in semi-rural Africa and slurp up any music I want to. I’m a lucky man.