Malaria and chickens
I had malaria once, and it was extremely unpleasant. I had been working in Yemen, but I actually contracted it when I was flying home on a Dutch airline that must remain nameless. The flight made a stop in Jeddah in Saudi Arabia, and the plane was parked out on the runway while waiting to pick up passengers – right on the edge of a mangrove swamp on the Red Sea coast.
The pilot turned the engines off to save fuel, and then opened the door to give us fresh air. It was night-time, and so a million mosquitoes swarmed into the plane. In five minutes everybody had been bitten multiple times. The passengers then revolted and the pilot shut the door and turned the air con back on, but it was too late.
I fell ill and collapsed a couple of weeks later, when I was at my wife’s family’s house in a small village in southern France, but I was lucky. My wife, who grew up in Africa, thought it was malaria, and the village doctor (who had served with the French army in Africa) confirmed it, so there and then he gave me a massive dose of antimalarial drugs.
By the time they got me to the hospital in Bayonne, they couldn’t even find any of the Plasmodium parasites in my bloodstream. They kept me in hospital for a couple of days anyway, but it wasn’t that bad, because in French hospitals they give you wine with your meals.
Small crisis, not many hurt. But the point of the story is that none of this would have happened to me (and presumably to some of the other passengers too) if only there had been chickens on the plane.
Statistics can sometimes lead to significant medical breakthroughs. In this case a team of Ethopian and Swedish scientists did a statistical study in three villages in western Ethiopia about the feeding habits of nocturnal, malaria-carrying Anopheles arabiensis mosquitoes. The results were instructive.
Outdoors, the mosquitoes preferred to feed on cattle (63 percent of bites), with human beings coming next (20 percent), and goats and sheep bringing up the rear (5 percent and 2.6 percent). Indoors, people provided 69 percent of the mosquitoes’ meals, compared to cattle at 18 percent and sheep and goats coming last again. (In this part of Ethiopia, people sometimes bring their animals indoors at night.)
There were also plenty of chickens around, both indoors and out. But in one outdoor sample, only one female mosquito out of 1,200 had chicken blood in her. In the indoor sample, none did. MOSQUITOES DON’T BITE CHICKENS.
Why not? Maybe evolution has taught mosquitoes to avoid chickens because chickens eat mosquitoes. But how do mosquitoes actually spot a chicken? Certainly not by sight: tiny compound eyes are good for spotting movement, but they do not give you much detail or any distance vision at all. So maybe by smell? That would be handy.
We can’t disguise ourselves as chickens, but we could try smelling like them. Or at least have something that smells chickeny nearby. In one experiment, the scientists even hung cages with live chickens in them over people’s beds at night, and lo! They had very few mosquito bites – fewer even than people sleeping under insecticide-treated bed nets.
Admittedly, this approach is a bit impractical for general use. Something more compact and less noisy would be preferable. So the scientists tried putting chicken feathers near people’s beds, and it still worked. Then they tried distilled essence of chicken odour (isobutyl butyrate, naphthalene, hexadecane and trans-limonene, if you must know), and that worked too.
Almost half the world’s population (3.2 billion people) lives in areas where malaria-bearing mosquitoes are present. About one in 15 of those people actually comes down with malaria each year, and almost half a million of them die of it. Many tens of millions more spend a long, agonizing time being very sick indeed.
Anything that cuts into those numbers would be most welcome, and prevention is much better than cure. CHEAP prevention is even better, and compared to insecticide-treated bed nets and various experimental vaccines, just sprinkling some “essence de poulet” (chicken fragrance) around before going to bed has got to be cheaper.
Essence de poulet probably won’t be on the market for a while yet, but hats off to Professor Habte Tekie of the University of Addis Ababa and Professor Rickard Ignell of the Swedish University of Agricultural Sciences, who led the Ethiopian-Swedish team that did the study. (Their full report is available online in the 21 July issue of Malaria Journal)
Meanwhile, if you want to bring a chicken along on our next camping trip, it’s fine with me. But don’t get the supermarket kind. They don’t work as well.