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Malaria is transmitted from man to man by the female anopheles mosquito, one of
the most capable vectors of human disease. Various species have been found to be the
vectors in different parts of the world. A. gambiae complex is the chief vector in
Africa and A. freeborni in N. America. Nearly 45 species of the mosquito have been
found in India and A. culicifacies, A. fluviatilis, A. minimus, A. philippinensis, A.
stephensi, A. sundaicus, and A. leucosphyrushave been implicated in the transmission
of malaria. The areas of distribution are different for these mosquitoes: A.
fluviatilis, A. minimus are found in the foot-hill regions, A. stephensi, A.
sundaicus are found in the coastal regions, A. culicifacies and A.
philippinensis are found in the plains. Species like A. stephensi are highly
adaptable and are found to be very potent vectors of human malaria. |
| The vector of
malaria that kills millions! |
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Mosquitoes choose the blood donor by
odours and visual clues and can learn from experience! Human behaviour also plays a role
and males are more frequently bitten.
The genome of A.
gambiae has now been cracked and the effort is expected to help in future research
into mosquito control strategies. [See]
Other diseases transmitted by Anopheles
mosquitoes: Apart from malaria, anopheles mosquitoes are also known to transmit W.
bancrofti (filarial worm); the Timorese filaria, Brugia timori; several
arboviruses including eastern and western equine encephalitis, Venezualan equine
encephalitis, onyong-nyong, tataguine etc.
How does a mosquito bite?
(does it 'bite'?!)
The female mosquito has a specialised
apparatus to penetrate the skin of its victim. At the end of the slender proboscis, there
are two pairs of cutting stylets that slide against one another to slice through the skin.
Once through the skin, the mosquito's proboscis begins probing for a tiny blood vessel. If
it does not strike one on the first try, the mosquito will pull back slightly and try
again at another angle through the same hole in the skin. Inside the proboscis are two
hollow tubes, one that injects saliva into the microscopic wound and one that withdraws
blood. The mosquito's saliva includes a combination of antihemostatic and anti-
inflammatory enzymes that disrupt the clotting process and inhibit the pain reaction (so
that the victim is unaware of the bite!) [See On malarial mosquitoes and mosquito bites at
http://scienceweek.com/2004/sb040416-6.htm;
Budiansky S. Creatures of Our Own Making. Science. 2002; 298:80-86.]
Why does a mosquito
need human blood?
The female mosquito lays 30-150 eggs every
2-3 days. Human blood is needed to nourish these eggs and Anopheles shows the most regular
cycles of blood feeding and egg laying. As a corollary, by using personal protective
measures against mosquito bites, like using mosquito nets, one can deny the blood meal and
hence help in mosquito control.
When does anopheles bite man?
Anopheles mosquitoes enter the house
between 5 p.m. and 9.30 p.m. and again in early hours of morning. They start biting by
late evening and the peak of biting activity is at midnight and early hours of morning. By
keeping the windows and doors closed between 5 p.m. and 10 p.m. and again in early
morning, one can prevent the entry of these mosquitoes into the house. Also protect
yourself against the bites in the evenings and early mornings by wearing garments that
cover the body as much as possible and at bedtime, by using mosquito nets without fail.
How far do the mosquitoes fly?
Mosquitoes can fly up to several
kilometers! And they can reach far off places by taking shelter in motor vehicles, ships
and aircraft.
How long do they live?
The average life span of a mosquito is 2-3
weeks. It can be longer in ideal living conditions.
Where do they hide?
The adult mosquitoes hide themselves behind
cupboards, clothes, curtains and other dark and cool corners during the day and come out
to bite at night. It is important to minimize these hiding places. Therefore keep the
cupboards and such other things closed; do not hang clothes at corners of the room,
instead keep them inside the wardrobes or cupboards.
Where do they lay eggs?
Anopheles mosquitoes breed in
natural water
collections. Therefore, breeding increases dramatically in the rainy season
when water collects in bottles, tins,
tender coconut shells, buckets, tyres etc., that are thrown out in the open and these
provide ample breeding ground. Also wells, ponds, water tanks, paddy fields etc., act as
breeding grounds. Construction sites provide ample breeding places for the mosquito -
water on the concrete slabs (used for curing), water collected in tanks, water collected
in and around the construction site owing to blockage of water drains - all these help
breeding. It is very important to destroy these water collections or to keep
them properly covered to prevent breeding.
How long it takes for the eggs to grow?
Usually it takes about a week for the eggs
to develop into adults.
For more
on Anopheles and its control, visit Ruth Sponsler's well laid site at http://www.anopheles.com
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