Dengue: The dangerous Asian tiger, yellow fever mosquitoes

Asian tiger and yellow fever mosquitoes are existing mainly because of us. We are the ones who are giving a chance for the mosquitoes to exist. For example, in barangays where the inhabitants do not have regular supply of water, they store water in metal drums and plastic containers without any cover. They do not know the principle that, if the mosquitoes could not find water, they are not able to lay eggs, which means no mosquitoes, no dengue illness and no death will occur.

Mosquitoes play a major role in the life quality and health of humans. They are tiny insects but the damage they brought to mankind is enormous. There are 3,200 species or types of mosquitoes in the world. Out of this figure, 1,000 species are considered carriers of diseases and more or less 60 are considered dangerous because they are responsible for the death of mankind.

One of these types of mosquito which is very dangerous is called, Aedes aegypti, often called "the yellow fever mosquito." Another is called Aedes albopictus, often called "the Asian tiger mosquito." These two types of mosquitoes are responsible for transmitting dengue virus to humans that lead to diseases called dengue fever, dengue haemorrhagic fever and dengue schock syndrome.

The Aedes aegypti mosquito is considered as the primary carrier of the dengue virus while Aedes albopictus is considered as the secondary carrier. The adult of these mosquitoes can be easily identified from other mosquitoes by the presence of white stripes or bands on the legs as well as on the abdomen, and both are day biters.

The female Aedes mosquitoes lay their eggs in clean and stagnant water (metal drums, cans, discarded tires, flower vases, gutters, leaf axils of banana, etc.). Each female mosquito is capable of laying approximately 200 eggs at one time in the water. Mosquitoes have four life stages:

1) Eggs - hatch for about 1 day; 2) larvae or locally called "pito-pito or ngoyo-ngoyo"-which last for about two to three days; 3) pupae-which last for one day; and 4) adult or the flying mosquito, which is responsible for transmitting dengue virus (lives for more than a month).

The whole process from egg to adult or flying mosquito is more or less one week considering that the temperature is more than 26°C, but if the temperature is cooler, then the development process would be slower.

Once an adult mosquito is developed, the female begins to look for human blood. A female mosquito has a special type of apparatus called proboscis (needle like structure) for sucking blood from humans, that's why, only female mosquitoes bite or suck blood because they need it for nourishment and development of their eggs. That means, only female Aedes mosquitoes are responsible for transmitting dengue virus to humans. On the other hand, male mosquitoes don't have proboscis and could not bite or suck blood from humans. They nourish themselves with nectar of plants.

There are about 2.5 billion people at risk and more than 50 million per year with approximately 500,000 per year are hospitalized that result to more or less 24,000 deaths per year from dengue and dengue haemorrhagic fever.

Although intensive efforts have been made to develop suitable vaccines against dengue, there is still no chance for success. The only way or possibility of controlling the disease is to control the mosquitoes that carry the virus.

The best way to control the mosquitoes is when they are still in larval stage or when they are still pito-pito or ngoyo-ngoyo, which are found in water (like barrels, discarded tires, etc.). The various ways to control them while they are in the water are:

1. For people who are storing water in barrels and plastic containers, they should cover it with nets or lids so that the female mosquito could not lay their eggs in the water. However, no matter how these barrels are covered sometimes, the mosquitoes could lay their eggs in the water especially when the household gets water from the containers. In this case, the households are recommended to clean these barrels and plastic containers at least once a week and apply B.t.i. tablets to the water to avoid the occurrence of pito-pito.

2. For vulcanizing shops storing old discarded tires, they are recommended to cover the tires with cellophane or plastic so that the tires will not be filled with water during the rainy season. In case the discarded tires have water, application of B.t.i. tablets is necessary.

3. For small plastic cups and other small receptacles that accumulate water during rainfall, they should be emptied. This could be done through environmental sanitation (cleaning the surroundings).

4. For pito-pitos in leaf axils of banana, applying B.t.i. tablets could control these.

All of various methods mentioned above could only be realized: 1. If people have knowledge about dengue - could be done through educational campaign with barangay health officers or health brigade giving lectures to the people especially the women in the barangays. 2. Community participation - if people have knowledge about dengue, they can participate in the activity. They should cooperate or participate in environmental sanitation because if only one family is cleaning its surroundings while the neighbors are not, then dengue fever will still occur. Aedes female mosquito can fly for about one kilometer just to search for human blood. Despite the control measures mentioned above, sustained "community participation" is still the strongest asset of a successful mosquito control. An integrated community-based approach, with volunteers from the village, is the most promising method of motivating a community to participate in mosquito control programmes.

Women can be of vital importance, since their participation enhances the possibility of reaching individual household and ensuring sustained community support. Of course, government coordination, close supervision, monitoring and evaluation, and teamwork with public health personnel, local volunteers, entomologists are necessary to reduce successfully the transmission of the dengue virus.

Finally, only through this approach that we can help save the lives of humans, especially children who are the hopes of our nation.