Guwahati,

Feature3

Small Bite, Big Threat!

 

Mosquitoes constitute the most important single family of insects from the standpoint of human health. They act as vectors of many diseases. A small bite of the mosquito can pose a big threat to human life. They are found all over the world. The four important groups of mosquitoes in India which are related to disease transmission are genera- Anopheles, Culex, Aedes and Mansonia. 

Mosquitoes and their Habits:
The body of the mosquitoes consists of three parts: head, thorax and abdomen. They have four stages in their life cycle: egg, larva, pupa and adult which complete within 7 to10 days. Eggs are laid on the surface of water, under favorable condition of temperature and food supply. In general, the Anophelines prefer clean water, the Culicines prefer dirty and polluted water; the Aedes prefer artificial collection of clean water and the Mansonias prefer water containing certain types of aquatic vegetation for breeding. 
The normal life span of an adult mosquito varies from 8 to 34 days. The males, as a rule, are short lived. Mosquitoes generally don't fly far from the place where they breed unless swept by currents of wind. Aircrafts and ships have increased the possibility of the dispersal of mosquitoes from country to country, and have created fresh problems of public health
The male mosquitoes never bite. They subsist on plant juices. The female mosquitoes are hemophagouse. They require a blood meal, once in 2-3 days for the development of eggs. Some species of females prefers human blood (anthrophillic), some prefer animal blood (zoophilic), and some feed on both human and animal . 
How Mosquitoes Transmit Diseases?
The female mosquitoes transmit diseases by biting a healthy person after taking blood meal from a diseased person or animal. When they bite a diseased person or animal, they ingest the infection causing microbes along with blood. The ingested microbes continue further development in the mosquitoes. When these infected mosquitoes bite a healthy person, the microbes get injected with the saliva of the mosquitoes to the blood of the healthy person and the person becomes sick.
Diseases Transmitted by Mosquitoes:
The Anopheles mosquito transmits Malaria (caused by parasites- Plasmodium Vivax, Plasmodium Falciparum, Plasmodium Malariae and Plasmodium Ovale), Filaria (caused by Nematodes- W. Bancrofti, B. Malayi and B Timori); the Culex mosquito transmits Japanese encephalitis (caused by  Arbo virus-JE virus), Bancroftian Filariasis, West nile fever, viral arthritis; the Aedes mosquito transmits Dengue and  Dengue hemorrhagic fever (caused by Flavy virus subtypes- DEN1, DEN2, DEN 3 and DEN 4), Yellow fever (caused by Arbo virus), Chikungunya and Chikungunya hemorrhagic fever (caused by Chikungunya virus), Rift valley fever, Filaria and the Mansonia  mosquito transmits Malayan filariasis.
Control of Mosquito-transmitted Diseases:
To control mosquito-transmitted diseases, we must prevent the mosquito bites and so the mosquito control measures need to be in place.
A. Mosquito bites control-  By undertaking personal protective measures like establishing physical barriers such as house screen, bed nets (insecticide treated nets), wearing appropriate clothing (boots, aprons, full sleeve shirts, long pants, head and neck covers) and insect repellents, one can protect from mosquito bites. 
 B. Mosquito control:  Mosquito control at larval stage, include elimination of mosquito's breeding places ("source reduction"), such as cleaning, throwing away, filling, leveling and drainage of breeding places (where water may be logged); killing larva and pupa by diesel oil, fuel oil, kerosene and chemical insecticides (Fenthion, Chlopyrifos and Abate); using larva-eating fishes like Gambusia Affinis and Lebister Reticulates. Adult mosquitoes can be controlled by spraying houses and fogging outside of houses with residual insecticides (Malathion, Propoxur (OMS-33), and to a lesser extent Gamma-HCH), and ultra low volume (ULV) space spraying of Malathione and Fenitrothione.
In recent years, control of mosquitoes by genetic methods, such as sterile male technique, cytoplasmic incompatibility, chromosomal translocations, sex distortion, and gene replacement have been explored. Their use is still in the research phase.
While there are many methods of mosquito control, experts now recommend an "integrated approach" that is, an approach which avoids the excessive use of any method but tries to combine one or more methods with a view to obtain maximum results with minimum inputs, and also to prevent environmental pollution with toxic chemicals and development of insecticide resistance.
(Dr. Dharmakanta Kumbhakar is a practicing doctor at GMCH and can be reached at 98645-17168 or by e-mail at [email protected])