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The Mosquito

 

To the naked eye, the mosquito may look like a quarter-inch long, fraction-of-an-ounce pest.  In reality the mosquito is a flying needle and punches well above its weight. Not only does this tiny creature carry serious disease and sometimes death, it has also become one of the leading impediments to economic growth in the developing world.

Mosquitoes will land unnoticed on your skin while you’re shopping in Los Angeles, taking photographs on Safari, or lying on a beach in Brazil.  You’ll feel an itch behind your knee and when you reach down, you’ll find a hot, raised welt.  You might well wonder whether the mosquito that just drained your blood left behind anything deadly. 

Human settlements encourage the evolution and adaption of mosquitos.  The Aedes Aegypti mosquito did not exist in America until it accompanied boatloads of slaves from Africa sometime after 1650.  The mosquitoes are likely to have travelled and thrived in the casks of drinking water and first tasted the blood of British and Dutch settlers via their new launch pad on a sun-baked Caribbean island.  The result in this case was Yellow Fever which spread to every port city in the New World, and there decimated vulnerable populations.

During military campaigns in the New World, invading armies were met with stiff resistance from Yellow Fever and Malaria.  English records show that more than half of the 12,000 troops sent to take Cartagena in Columbia in 1742 were felled by illness.  The same fate awaited the French who killed over 150,000 Haitians but themselves were defeated by viral outbreaks. Out of a force of 29,000, only 6,000 saw Europe again.


Until the Nineteenth Century, few tropical diseases had any associated physical disfigurement associated with the infection.  Along came the Culex Pipens in the sailing ships again to India and the Far East carrying with them larvae from the filarial worm, and its epidemic time again.

The British realised that if they could not control mosquito-borne diseases, they could not rule India.  Without quinine the British would not have been able to maintain an Empire. It took years of research and much circumstantial evidence to link many communicable diseases with mosquitoes, but it eventually became certain that the microfilaria a mosquito ingested with a blood meal was the first developmental stage before being transferred to an unsuspecting human host. 

The results were devastating.  No-one who confronts a patient suffering from the resultant elephantiasis ever forgets it.  The disease occurs when the flow of lymphatic fluid is blocked, and parts of the body – generally the legs or genitals – swell enormously. Under the pressure of swelling the skin stretches until it becomes papery thin.  Fluid collects often forming sheaths that flow from a person’s hips down his legs. The accompanying photograph gives you some idea. 

In 1999 New Yorkers learned the first law of mosquitoes: expect the unexpected.  Until then most residents city residents found mosquitoes to be an occasional airborne pest to be swatted and endured.  But somehow a common house mosquito, the culex pipens, that usually hangs out in storm drains and rarely bites people, acquired an exotic virus that could cause a fatal brain infection – West Nile encephalitis. The virus, named after its discovery in 1937 in the blood of a feverish woman in the West Nile district of Uganda, had never been seen across the Atlantic before.

How did it get there?  Did it hitch a ride on a ship or in a plane?  Did it enter by way of an infected traveller? Did it use local mosquito species first as an incubator then as a transport system for infecting countless people?  We may never know the reason.  What we do know is that medical research has just discovered a new surprise and that it may happen again and again with a variety of new viruses.

Hard as it might feel to sympathise with mosquitoes, they encounter the most hazardous of beginnings.  Incubated over only two days, they emerge as long wriggling larvae with whiskered heads that hang down in the water to feed, their tails equipped with a breathing tube that takes in air. 

In the few days it takes for them to transform into flying bloodsuckers, they must survive any changes in temperature, as well as attacks from hungry fish, water striders, whirligig beetles, and of course from birds the moment they take flight.  More larvae die from disease and predation than survive, but the sheer volume of numbers has ensured their continued survival.

Whether it be mosquitoes accompanying slave ships to the Caribbean, travelling in re-tread tyre containers from Japan to Houston, or in the hold of a transatlantic flight, mosquitoes have spread around the globe from their original habitats, ably assisted by the trends of human populations.   It’s not just a Third World problem – in recent years 87 cases of malaria have been reported from 12 separate countries within a few miles of the main airport, including Heathrow. And we haven’t even projected where the mosquito may go with global warming

Dr Andrew Spielman, a Harvard professor and world authority on mosquitoes says “There’s no need to reach overseas for exotic viruses transmitted by mosquitoes.  There’s an enormous number of viruses here now that could bridge from animals to humans via the mosquito.” 

Mosquitoes:  some basic facts:

-         The mosquito has been around for 170 million years, since the Jurassic period.  It’s ironic that the mosquito used in the film Jurassic Park appears to be a Toxorynchites, one of the larger species that never drank blood.

-         There are 2,500 known species of mosquito. They are not shy: some bite in the morning; some in the midday sun, some in the evening and some at night.  No hour of the day is mosquito free.

-         Mosquitoes can live to the grand old age of 6 months.

-    The Anophales mosquito transmits malaria; the Aedes Aegypti transmits Dengue Fever  and Yellow Fever; Culex Pipens transmits West Nile Virus and Filariasis.

-         It is always the female of the species that carries and transmits these diseases.

-         Mosquitoes cannot carry the AIDS virus, but is it a matter of time before they develop this ability?

"Mosquitoes stopped their mighty armies, crippled their administration and killed millions. Soldiers would die, movement of troops became impossible. Labourers would die," says Nand Lal Kalra, head of the Mosquito Museum in New Delhi.

"It was an endemic cycle of poverty, famine and epidemic. Growth stopped. Development came to a halt as labourers died in thousands and region after region became virtual black holes - uninhabited and barren. Whether it was laying a railway line or building a factory, malaria destroyed everything. In 1920, the British abandoned a massive river canal project for six years when malaria killed hundreds of labourers.” 

Next time you are buzzed by a mosquito, remember that waving your arms will only work against you.  Your scent tickles the mosquitos antennae, your movement catches her eyes and the heat generated by your movement guides her to that bit of flesh not covered by clothing.  Once it has alighted, the mosquito may probe your skin as many  as twenty times, in order to find the best angle to your blood. 

We still have much to learn about the mosquito: why it needs our blood for reproduction; how it distinguishes between a horse, a bird and a human; how it develops the sucking force required to extract the blood of its victim through a tube so infinitesimally small and how it has so easily adapted to man-made pesticides, change of habitat and climate change.   Everything about its design is economical and precise. Maybe its beauty lies in these mysteries. 

Graeme Dinnen

The best advice for avoiding mosquitoescomes from ‘What Doctor’s Don’t Tell You’ :

'Just use a mosquito net, not drugs!'

With many thanks to Dr Andrew Spielman and Michael D’Antonio, authors of an amazing book entitled “Mosquito” from which much information has been sourced.  It may be science but it’s also a page turner!  When I last looked there were copies available for only 1 pence!


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