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Mosquitoes in Southeast Asia

Posted in Animals, Latest of Asienreisender with tags , , , , , , , , , , , , , , , , , , , , , on July 27, 2013 by Thim Kwai

Health Concerns

Tourists and Travellers who come to Southeast Asia are usually very concerned about safety and health. It’s generally more safe here than in most other parts of the world and generally easy to remain healthy; the dangers are mostly overestimated or self-caused.

Nevertheless I want to point out one potential threat here.

More dangerous than all the scary animals like tigers, cobras, king cobras, crocodiles and so on are the mosquitoes (Spanish / Portuguese for ‘little fly’), or at least a few certain kinds of mosquitoes who transfer dangerous diseases. The verymost kinds of mosquitoes do not transfer diseases, although, in more seldom cases, they can cause various other infections when transmitting bacterias, viruses or other parasites into the human body.

Various kinds of mosquito – transmitted tropical diseases are malaria, dengue fever, chikungunya fever, yellow fever, West-Nile fever, Rift-Valley fever, encephalitis and more. Some mosquitoes transfer parasitarian worms who can live in the human vascular system. Even HIV/AIDS can still not be completely excluded from the list of diseases transmitted by the nasty insects, but it’s at least considered highly unprobable.

Apart from these health threats mosquitoes are simply annoying and can spoil enjoying time or cause sleepless nights.

Mosquito Habits

The oldest known mosquito remain discovered until now is some 79 million years old. It’s imbedded into a piece of amber.

Although generally very small animals, some of them reach a size of more than 15mm.

The number of different kinds of mosquitoes in total vary between 2,500 and 3,500 species, they appear worldwide except in the polar regions and in deserts. They breed at waterplaces of all kind. In the swamps of Siberia, Canada and the north of Europe they appear in the summer month in masses and are much bigger and their bites leave a much bigger impact on the skin than the ones in Southeast Asia. Therefore they are much less dangerous in the north than in the tropical regions of the globe. Particularly the anopheles (malaria) mosquito is a very small representative of his kind. When sitting on walls or the skin it’s body shows a peculiar angle of some 45 degree to where it sits on, what makes it distinctive from other mosquito types.

Mosquitoes do not feed from blood, but from nectar and fruit juices. Only the females suck additionally blood. They need the containing proteins for their eggs. A ‘blood meal’ of a female mosquito is sufficient for around 100 eggs, who are layed two to three days after it. In their lifespan, which lasts several weeks, a female mosquito can produce 1,000 or more eggs in her life. Though, there are also kinds of mosquitoes who don’t bite humans but exclusively animals, and a few others who don’t bite at all.

They lay their eggs one by one on the surface of calm, preferable clear water. The development from egg via larva and pupa to a flying mosquito takes about two weeks.

Their rostrums contain two canals. One is injecting a protein containing saliva for a first, external digesting or preparation of the blood, through the other canal the mosquito sucks it’s meal up. The injected protein leads to a small allergic reaction and the well-known itching swelling. If the bite hits directly a nerve, the bit can trigger a small pain. It’s, by the way, said that the bite of a female anopheles (malaria) mosquito is particularly itchy.

Everybody made already the experience, that some people attract mosquitoes more than others do. That has to do with the human smell, which attracts the animals. The smell of lactic acid and other substances on the skin and in sweat serves for their orientation. When they are already close to humans, they also orientate visually and on body temperature.

That explains an observation frequently done while hiking in the jungle. Jungle trekking is a sweat-driving activity. Soon many mosquitoes are attracted and buzz around one’s head.

Male mosquitoes are in average 20% smaller than females, and they have bushy tentacles. As already mentioned males are not able to bite.

Most active mosquitoes get at warm, calm days without direct sunlight. When it gets too windy, they can not navigate anymore. That’s why they have problems with ventilators. When it’s too cool (10 degree or less) they get numb and paralized. They particularly dislike air conditioners.

Mosquitoes can fly over distances of several kilometers. Their speed can be considerable; it’s sometimes remarkable how quick they can disappear when being hunted. They manage to fly closely along walls, tree stams etc. to get cover and their trajectory is often very twisting and unpredictable. If the wind is favourable mosquitoes can fly as high as a hundred meters.

Mosquitoes are generally most active in the evening around sunset, sometimes in the morning, but can additionally appear at all times at day and night. Malaria mosquitoes are night active, while the ones transferring dengue are day active.

Mosquito Control and Practical Prevention

Fighting mosquitoes has a long tradition. For example the drainage of swamps detracts the basic for mosquito reproduction. An oil-film on breeding-waters stifles the mosquito larvaes. But it’s damaging the ecosystem as well, as many other approaches do. The problem of chemical treatments is always that not only the targeted mosquitoes but a lot of other species are also affected, if not whole biotopes. In many Southeast Asian countries DDT is still in use, while it is abolished in western countries since years (Stockholm Convention) and well known for it’s desastrous side-effects.

Another problem of chemical treatments are the growing resistances. DDT, supposed to be a superior mean against malaria in the 1950s, lost more and more effeciency over the following years being used.

Gentechnical approaches try to modify mosquito genes so that they can not reproduce anymore. Another approach is to make the mosquitoes themselves disease resistant, so that they can not serve as a host and transfer diseases as malaria and dengue fever anymore.

Dragonflies are very effective, hunting and eating mosquitoes at all stages of their development (eggs, larvaes, pupaes and adults). A number of other animals, insects, amphibians and fish eat mosquitoes or their spawn.

In Thailand I have seen the application of pesticides (presumably DDT containing) in great scale by troops of communal workers who used massive sprayers all along the river banks of the Mekong River and the inner town of Chiang Khong. Considered that all the housings, kitchens and restaurants are mostly open, it’s a very brutal way of dealing with mosquitoes. Not to mention that the pesticides get into the drainage system and the river later. Besides I didn’t see a relief in the mosquito plague in the following days.

There are many methods to prevent and fight mosquitoes in all-day-life, but still many people don’t care for that. First it’s helpful to avoid standing waters like little pools, flowerpots, tyres and so on catching rain water whenever possible, or to set little fish (like guppies) in them who eat their larvaes. It’s good to keep kitchen and kitchen surroundings clean, particularly from rotting fruits or fruit remains.

Above all one needs is to carry always a repellent in the pocket. Repellents are available in many shops in most places for small money. If you see mosquitoes around or you get a bite already, it’s best to use it immediately. The beasts target mostly for the ankles. At nighttime it’s best to apply a repellent on all parts of uncovered skin.

The most repellents are based on DEET. DEET is a chemical which is in use against mosquitoes since 1946 (developed by the US army, used much in the American Vietnam War) and since 1965 sold in the civil sector. The repellents I find in Southeast Asia are often pretty weak, containing 7%, 11% or 13% DEET. In western countries repellents contain 30%, sometimes up to 50%.

It’s yet not completely clear why actually DEET repels mosquitoes, but it has to do with the smell. Either the part of the human smell which attracts the mosquitoes is blocked in their reception, or the smell of the DEET itself causes the insects to stay away.

Side effects of DEET are possibly allergic reaction, insomnia, erratic mood swings and receptional irritations. It’s recommended not to be used by pregnant women and babies (below two years old).

One does not necessarily need a mosquito net. At warm nights a mosquito net queues the air and causes stifling air. On the other hand a mosquito net prevents from more than mosquitos – namely other animals who may creep around and might find the way into ones bed.

Know…

This is only a part of the illustrated article ‘Mosquitoes in Southeast Asia’. Read the whole article on Mosquitoes in Southeast Asia by Asienreisender.

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