Fight the bite

The mosquito is an insect in the family Culicidae. The name comes from Spanish and means ``little fly''. There are over 3000 species that are found throughout the world, except in cold regions or at high altitudes. Most mosquitoes can travel up to 10km during a single night, and fly continuously for one to four hours at a rate of one to two kilometers per hour. Their life cycle consists of four distinct metamorphic stages: egg, larva, pupa, and adult.

One reason mosquitoes don't grow in fast moving water or fountains is because the new adults must rest on the surface of the water until they dry and their exterior body parts become hardened before they can take flight.

Why so dangerous?

The female mosquito inserts the tip of her proboscis - magnified here thousands of times under an electron microscope into the victim to suck its blood. The proboscis contains six parts: two pairs of sharp, flexible "knives" that surround a pair of hypodermic needle-like tubes - one for sucking up blood, the other for dripping a chemical into the wound that keeps the blood flowing.

Mosquitoes are vectors. This means that they carry parasites and viruses. They don't actually kill people themselves; they simply transport deadly diseases to the victim. The parasites and viruses that the mosquitoes spread kill millions and make millions more very sick every year.

Only the females ``bite'' humans, mammals, birds and occasionally reptiles by injecting tubes called the proboscis, which is similar to a hypodermic needle, into their victim to suck its blood (hematophagy). Therefore they don't ``bite'' at all. Only the female has the proboscis. Females do not require blood for survival, but they do need supplemental protein to develop and lay their eggs. Both male and female mosquitoes feed on nectar from plants, which is fine as a meal for adult mosquitoes, but since nectar doesn't contain protein, a blood source is essential for the female to produce her young.

Mosquito related diseases

The most prevalent disease spread by mosquitoes is malaria. Malaria is a single-celled parasitic organism called a plasmodium. The plasmodium multiplies in red blood cells and causes a flu-like illness that, if untreated, can cause death. It is estimated that, aside from wars, malaria is responsible for the deaths of half the number of humans that have ever lived! That is astonishing. Though treatable, maleria still kills over two million people a year.

The genus Anopheles is responsible for the spread of malaria. Although Bangkok is free from Anopheles mosquitoes the jungles near the Cambodian and Burmese borders are home to these mosquitoes, so care should be taken when traveling in those areas.

Another disease spread by mosquitoes is the yellow fever virus. Unlike malaria which is carried in the gut of the mosquito, yellow fever is carried in the saliva of mainly the Aedes genus of mosquitoes. There are many potential symptoms of yellow fever, such as flu-type side effects, kidney failure and internal bleeding, but as the virus reproduces best in the liver, hepatitis is often the result. Hepatitis causes the patient to develop jaundice, a yellowing of the skin. Yellow fever has not made it to Asia and is restricted to Africa and South America, despite the Aedes mosquito living in Asia.

Japanese encephalitis, an inflammation of the brain that can lead to death, is also spread through the saliva of mosquitoes. This disease is present in Thailand. Most infections are resolved early without leading to fatalities.

Dengue fever is also found in Thailand and spread by Aedes mosquitoes. Dengue fever causes rashes, nausea, vomiting and blood in vomit and feces. Today it is rarely fatal, but in 2005 at least 12 Thais died as a result of an epidemic here.

These are only four of many diseases that female mosquitoes spread in their relentless search for blood, so how can you stop them?

Protection from mosquitoes

Larvae of 'Culex' Mosquitoes. As seen on the picture, larvae make dense groups in standing water.

There is no way to completely prevent mosquitoes from ``biting'' you. Repellents that contain DEET, a complex synthetic chemical, are very effective. Natural pesticides such as citronella and eucalyptus also keep mosquitoes away for a short while.

Interestingly, the above solutions don't really repel mosquitoes, they either mask your natural scent so the mosquito doesn't realize you are there or, in the case of DEET, simply disorientates the mosquito when it smells the chemical.

The best prevention is to wear light-colored clothing and to cover your ankles and arms, and to wear a hat at dawn or dusk. If you are camping, mosquito nets that are permethrin-impregnated are excellent, but be aware that mosquitoes often hide in clothes and containers, and under your bed, so they may still get you!

Are you attractive?

Mosquitoes are not attracted to a particular skin or hair color, but some people are more attractive to them than others. What exactly makes some people more attractive than others to mosquitoes remains a mystery. Mosquitoes are more attracted to the carbon dioxide we exhale, our body heat, perspiration, and body odors.

The mosquito is so hated that the pesticide DDT was once used to annihilate them en masse, but it was later determined that the pesticide had more biological side-effects than the dreaded mosquito.

As a prevention against the diseases mentioned above, you can get vaccinations for the viral strains. Vaccinations against Japanese encephalitis should be given as part of a child's immunity course in Thailand. As for malaria, no such vaccine exists. There are many drugs that combat malaria but the plasmodium is evolving quicker than the drugs are developing.

Itchy, scratchy feeling

When a mosquito bites, you rarely feel it because its saliva contains a mild anaesthetic that desensitizes you to the bite, along with an anticoagulant. The anticoagulant stops your blood from clotting so she can feed freely. She only takes in about five microliters of blood per serving, which goes directly to her abdomen.

When a female injects her proboscis she injects saliva, which contains proteins that cause a reaction similar to an allergy. The area swells and you itch.

People often ask what is the purpose of mosquitoes. They don't really need a purpose; they just exist with the aim of passing on their genes as best they can, just like every other living organism. They are quite prominent in the food chains of many animals though, who would no doubt miss them they were not around.

For more information, visit How Mosquitoes Work at http://tinyurl.com/2wh87c .