Fri, Aug 24, 2018 - Page 8 News List

Better ways to avoid dengue fever

By Emilio Venezian

A report on dengue fever in New Taipei City is wearisome not so much because it acknowledges the presence of the disease, but because the advice and precautions seem to stem from sources that are not particularly familiar with the ecology of the mosquitoes that spread the disease (“Dengue alert for New Taipei City,” Aug. 16, page 3).

In urban areas the disease is spread primarily by Aedes aegypti, or yellow fever mosquito, although other species of Aedes are known to have been involved.

I happen to be familiar with the subject because I led a study, sponsored by the Pan American Health Organization, about the eradication of Aedes aegypti in the Americas.

Aedes aegypti likes to live in proximity to people, and prefers clean water for laying its eggs and letting the larvae grow after the eggs hatch.

Elimination of stagnant water is sound advice, but it is not enough: It does not cover some potentially useful alternatives and it shirks the government’s responsibility for public health.

People often interpret the adjective “stagnant” to mean “foul” or “dirty,” rather than “not moving.” Moreover, people do not automatically think about where clear stagnant water could be present: in quiet pools in small streams, in discarded soda cans, cardboard or plastic cups, and open-mouthed containers after rain, in clogged gutters around the house, in discarded car tires thrown anywhere or used to stabilize roofing against strong winds, just to give the most salient examples that are found in the US.

The mosquitoes also hatch in various types of cisterns and other containers used to catch water from rainfall or from rivulets coming down from mountains, as in Brazil and the Caribbean islands, or in abandoned machines, such as refrigerators, washing machines or cars abandoned along the highways.

In my neighborhood in New Taipei City there must be a decorative stream or pool for every 10 houses, although protective walls make it difficult to be sure. We have a lot of mosquitoes of unspecified species.

It is unrealistic to think that you or I are responsible for what our neighbors do. Much of that is something that only the government can do effectively. It is not clear that it is doing it at all.

Brazil, in its control efforts, required that every rainwater barrel and rooftop cistern be inhabited by fish that prefer to eat Aedes aegypti larvae, with owners subject to destruction of the container and a heavy fine if a periodic inspection by health officials found no fish.

New Orleans once controlled an epidemic of yellow fever — another viral disease spread by Aedes aegypti — by having squads throwing handfuls of salt at roofs that appeared to have clogged gutters.

In Texas, towers were built to provide housing for bats, so they would eat the mosquitoes. Those measures, although quaint and perhaps slow, did work.

A more modern method is to spread sand covered with the larvicide Abate in pools, and even streams. At the concentrations needed to control the mosquito population, the insecticide is not harmful to plants, animals or people.

Using insecticides inside the house is also a good idea, but you must remember that the mosquito is shy and likes to hide behind furniture, pictures and paintings, so you must spray quite thoroughly.

The article asks people to seek medical attention, but better motivation would help.

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