Why do certain people attract mosquitoes?

Tuesday, November 17, 2009

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Dr Cameron Webb, Sydney University's resident mosquito expert, has prepared a box full of mozzies — and he's looking for some human fists to put in his little box of horrors.

Andrew is joined by Cameron and his friend Peter who are also up for the challenge.

Each participant will put their arm in the cage for a minute or so and count how many mozzies are landing on the arm and then compare the results.

When the results are tallied:

  • Cameron: attracts nine mozzies.
  • Peter: attracts eight.
  • Andrew: only two.

So why is Andrew any different from the other two men?

"It's maybe a different mix of odours coming off your skin, there's a whole lot of reasons but it certainly seems you're not as attractive as Peter and I," says Cameron.

So the mozzie magnet theory is true after all — but there's another development.

Within a minute or so of being bitten, Pete has had a reaction to the mosquito bites by coming up in a red welt. How come Dr Webb and Andrew's skin didn't react in the same way?

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Test two

CrosstrainerStill at Sydney University, this time the men prepare for their next mozzie test by hitting the cross-trainer. Why? Because mosquitoes are attracted to the chemicals our body secretes. Therefore Cameron, Peter and Andrew are having a good workout to see if the smell of human sweat will change their individual attractiveness to the mozzies.

Andrew's hand goes back into the box. For the first test, a sum total of two mozzies came over for a look. But the addition of sweat into the mix has made the mozzies even less interested in Andrew.

Next up, Peter puts his arm in the box. But poor Peter is this time trying to shake them off straight away as they latch straight on. No less than eight mozzies jump aboard for a feed — and Peter's forearm is blowing up like a bright red balloon in there.

Peter is suffering an allergic reaction to the mosquito saliva that's injected when the mozzies are feeding — and that's a key finding because not only is he a mozzie magnet, he's a really allergic magnet.

"Obviously to look at Pete's arm it looks like it was bitten by a lot more mosquitoes than mine. But in actual fact we were bitten by almost exactly the same amount of mosquitoes," says Cameron.

So the same amount of mosquitoes could be biting two different people at the same barbecue but one person might think that they're being bitten more because they're reacting in a different way. Everybody differs in the way they react to the mosquito saliva that's injected when they take a blood meal.

Test three

Alcohol consumptionThis time Andrew wants to drink a couple of beers then dive back into the mozzie box to see if he's be more attractive to them now. Some experts believe drinking alcohol makes your skin give off a chemical that attracts mosquitoes.

It appears that this theory could be true: Andrew has quite a few more feeding from him and ends up with eight mozzie bites instead of two. It would seem that drinking alcohol has made him four times more attractive to these annoying bugs.

However, Cameron is sceptical: "The amount of mosquitoes that are ready to feed changes during the day and Pete and I were sitting around while you were drinking there for a while and in the meantime I think the mosquitoes probably got a little hungrier."

Yes, some people are mosquito magnets and a lot of people are allergic to mosquito saliva. So when their skin flares up, they can wrongly assume that they're getting bitten more than the next person.

The bad news for people in this category? There's no effective alternative to mosquito repellent. All you really can do is wear long sleeves and throw in a bit of mozzie repellent.

Mosquito facts

  • Mosquitoes don't bite us at all, they actually suck the blood out of you.

  • Mozzies can transmit Ross River and Dengue Fever — but they can't transmit HIV. The reason? The virus that causes AIDS can't survive in the mosquito.

  • If you're a tasty bite for a mozzie you could be in trouble. There are four hundred species of mosquito in Australia, 40 in each State's capital city and at least five in the typical suburban backyard.

  • The female species is more deadly than the male mozzie. They need the blood for protein to make eggs.

  • A mosquito bite can be fatal because of the diseases they carry. Malaria is of course the best known killer, more than a million people die from this parasite every year. Spread by the anopheles mosquito, it occurs in tropical and sub-tropical areas of the world. But it's not yet a danger in Australia. Instead, Australia gets its fair share of Ross River and Dengue Fever cases, which can also sometimes be fatal.

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