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DENGUE in INDONESIA

Introduction

Dengue in Indonesia is a cyclical disease, varying from month-to-month and year-to-

year. The graph above of monthly dengue cases and deaths shows this. There is almostalways an annual peak occurring in the rainy season (Jan-Apr). The peak passes after 2-4

months, followed by a decline of 8-10 months centered on the dry season. The year

following a high peak is almost always lower, as occurred in 1998/99, 2004/05, 2007/08.

In Indonesia, in dry season the Aedes mosquito cannot find breeding sites outdoors lack

of rain leaves dry tyres, containers, and other collections of rainwater. The mosquito can

only lay eggs indoors in Sink bath and other tanks of water, potted plants, etc. When the

rainy season starts, the outdoor containers fill with rainwater, the mosquito expands itsbreeding outdoors, the number of mosquitoes increases.

Immunity

The difference in peaks from year-to-year probably relates to human immunity or what is

called herd immunity, that is the average percentage of immunity in a population.

Dengue infection causes immunity against the disease, but there are 4 types of dengue(serotypes). After having one serotype, a person is resistant to infection against that

serotype. Most evidence suggests immunity is long-lived, perhaps for life. This means a

person could have dengue only four times in his life.

After a big outbreak in one season, many people will have had dengue. Next year thereare few remaining susceptible, unless a new serotype is introduced. It takes several yearsfor a fresh group of babies and children to be born, until the numbers will sustain another

outbreak.

Another factor is migration of people. We are experiencing large population movements

which brings many new people to the cities, people who may never have experienced

dengue. They also build up the number of susceptible people over time.

This also explains the irony of dengue in Singapore that successfully controlled dengue

by controlling the breeding sites of Aedes mosquitoes. After many years, there arose a

large population of susceptible people. When a change in breeding led to increase ofAedes, along with introduction of the virus, a large outbreak followed.

Incidence of dengue in dense population centers

25% of the cases in Indonesia are recorded in DKI Jakarta,

20% in Banten and Jawa Barat, the two provinces surrounding Jakarta.

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14% in Jawa Tengah, and 15% in Jawa Timur.

Altogether 75% of the cases come from the 6 provinces of Java.

Bali contributes 5%, and then the other 26 provinces contribute the remaining 20%.

Dengue control: Fogging (thermal or ultra-low-volume production of a cloud of insecticide in the

air) only works against flying adult mosquitoes, not against eggs and larvae. The

day after fogging cancels whatever good effect happened during the fogging.This is because the numbers of new mosquitoes replace many times over the ones

that are killed.

Each female mosquito lays 50-300 eggs every 2-3 days (after feeding on blood).The eggs take about 9 days to hatch out a new generation of mosquitoes. When

one female mosquito is killed, she has already put 3 batches of eggs to incubate in

water. A new generation hatches each 2-3 days, so one female will have 150-900

eggs to replace her within days.

Fogging outdoors will temporarily reduce the population of nuisance mosquitoes(primarily Culex species) without affecting Aedes.

On top of the numbers, there is transovariol transmission. The mother passeson the virus to the eggs directly, so the progeny are hatched infected.

Source reduction

indoor space-spraying

Some trials have shown an effect on dengue when insecticide fog (such as flitsprayers) is systematically used indoors, spraying in closets and other hard-to-reach

places, that Aedes mosquitoes use for hiding and resting. Even if effective, scaling

up from small-scale trials is always difficult.

Link:

http://www.who.int/topics/dengue/en/