The buzz on mosquitoes: The health risks we ignore
As TV presenter Charlie Webster is struck down with malaria in Brazil in the run-up to the Olympics, her plight highlights the risks too many people ignore
Published 23/08/2016 | 02:30
They have been buzzing around this planet for some 400 million years, and there is a high chance at some point you have been bitten by one of the 2,700 known species of mosquito.
For the most part, this is nothing more than annoying, but they can also be spreading dangerous and deadly diseases, including malaria, but also dengue fever and the much-feared Zika virus.
Last week, it was reported that the British TV sports presenter Charlie Webster was in a coma after contracting a rare form of malaria during a charity bicycle ride through Brazil.
The fight against mosquitoes and the diseases they spread is a focus of intense scientific research. Just last week, the US Federal Drug Administration approved a project in which genetically modified Zika-fighting mosquitoes will be released into the Florida Keys area, which scientists believe could eventually impede the spread of the virus. But still the majority of us remain ignorant to their power.
A survey conducted by the London School of Hygiene & Tropical Medicine (LSHTM) this year found that 74pc of people travelling to tropical locations didn't seek any advice about mosquitoes or even pack repellent.
Last year, it was reported that Ireland had the third-highest rate of imported malaria in the EU, topped only by the UK and Belgium.
Here, we ask James Logan, associate professor in medical entomology at LSHTM, and presenter for Channel 4's 'Embarrassing Bodies' series, about our most burning mosquito-related questions.
Why do some people attract them?
Bigger people do get bitten more - perhaps because there's simply more of them but beyond that, it's about how we smell, says Professor Logan. His team took people who said they always get bitten - who they refer to as 'attractive' - and those who say they never do - the 'unattractive' ones - and connected micro-electrodes to the antennae of mosquitoes to see what they were smelling before they took a bite from them.
"The attractive people's bodies contained more of a type of chemical called kairomones, while the unattractive emitted more chemicals called allomones that repelled mosquitoes. Creating products based on these chemicals are now being tested," says Logan.
"The aim is to develop a drug or pill that you take before you go on holiday that causes the body to produce these natural repellents."
As for what determines that chemical make-up, much is down to genes. Last year, Professor Logan published a study that compared groups of twins and how they reacted to mosquitoes. "The identical ones were very similar and the results suggested that attractiveness to mosquitoes was strongly controlled genetically."
What about delayed reactions?
When you first get bitten, a mosquito injects a cocktail of chemicals into your skin which are also an anaesthetic so you don't feel them bite.
"The first time you get bitten, your immune system doesn't react," says Prof Logan. "If you continue to be bitten, then you will develop a reaction some time with welts or those itchy red lumps."
Continue to get bitten beyond that, however, and you may not react at all.
"A lot of our scientists here do their work by putting their arms in cages full of mosquitoes and have done that so many times they don't react anymore."
It's why when you go on holidays you may get lots of angry bites while the locals are walking around with nothing. "They're being bitten, but just not reacting because they're desensitised."
How can I stay safe?
The main malaria mosquito is the anopheles gambiae and that which transmits the viruses Dengue, Zika, Chikungunya and Yellow Fever is known as the aedes aegypti. Other than the former having black and white stripey legs, they're hard to spot by the untrained eye.
"So, if you're in an area where these diseases are present, presume all mosquitoes are dangerous," says Logan. If you're pregnant or planning to become so, avoid anywhere with Zika virus because children in the womb are at highest risk. If you're going somewhere with a malaria risk, taking anti-malaria medication can help, but some tablets need to be taken three weeks before you travel and there can be side effects.
No malaria tablet is considered 100pc effective, says Logan, so "it is important to avoid contracting malaria by not getting bitten by the mosquito that carries it".
Right now, he says, there is a vaccine for Yellow Fever but nothing for the other illnesses - yet. According to a spokesperson for the drug company Glaxo Smith Kline, who are developing the RTS,S vaccine for malaria: "Following large-scale scientific trials… the World Health Organisation recommended that RTS,S be introduced through a pilot roll-out in children aged five to 17 months, which could begin in several African malaria-endemic countries… in early 2018."
Meanwhile, keeping the mosquitoes away is your best defence.
So what works?
Although DEET has been around as an insect repellent since the 1940s, when it was developed by the US government for their army during World War II's jungle warfare, little compares to it in effectiveness, says Prof Logan. "If you're travelling to a high-risk country - sub-Saharan African countries, certain areas of South America and even some parts of Thailand - look for repellents containing 20-50pc DEET," he recommends.
DEET began life as an agricultural pesticide and many simply don't like using it because of the strong chemical smell. A proven alternative is -p-menthane-diol, or PMD, which is oil of lemon eucalyptus.
"Look for about 30pc PMD but do be aware that it will need to be re-applied more frequently than DEET, every three to four hours." Other active ingredients in repellents proven to work include picaridin and IR3535.
Other protective measures?
Always sleep under a mosquito net, ideally impregnanted with insecticide, (malaria mosquitoes are most prevalent from dusk to dawn). New clothing ranges impregnated with mosquito repellants have been shown to work, and brands include the Nosilife range developed by outdoor-wear company Craghoppers.
What about Marmite and other mozzie-repellent folklore?
"We've tested [eating] garlic, [taking] vitamin B and [eating] Marmite and none of them worked," says Logan. "People also talk about alcohol but the only evidence we have is that beer could increase our mosquito attractiveness."
What does it feel like to have malaria?
Sharon Forbes, 61, lived in Kenya for 17 years with her husband Colin, who still lives there and works for an Australian mining company. She contracted malaria three times during her time there.
"Malaria can vary in severity. The first time I had it was mild and passed within two days. But the second, the terrible symptoms came on quickly - violent headache, excruciating neck pain, nausea - and progressed fast. Within an hour I was vomiting every 20 minutes and alternating cold shivers with fever and I had the most unbearable aches and pains.
"The third time, I contracted the most serious form - cerebral malaria. I had two false-negative tests and wasn't diagnosed until four days after my symptoms appeared by which time I was so ill, my parasite count so high, that I was convinced it was the end. Every part of my body ached, I was being sick constantly.
"The ironic thing was that both times I was treated, as soon as I was put on a quinine drip - the standard treatment for malaria - I got better within days.
"In Africa, it's considered much like getting flu is here. It's perhaps why my husband Colin didn't panic when I had it - he's had it four times himself. Yet the tragedy is that every two minutes, a child dies from malaria. One day, with more education - and perhaps a vaccine - as well as the work of the Malaria No More charity, I hope we can beat it."