SRI LANKA: Dengue deaths drop, but health officials urge more vigilance

Photo: Christine Jayasinghe/IRIN

A local authority employee sprays insecticide in a home garden in the Sri Lankan capital Colombo as part of a dengue control programme

COLOMBO, 8 January 2009 (IRIN) - Four years after Sri Lanka's worst outbreak of dengue fever, fewer people are dying of the mosquito-borne disease, but health officials caution that more public action is needed to prevent epidemics.

The number of fatalities has been dropping since 2004 when 88 people of the 15,334 known to have contracted dengue died of the illness. In 2008, some 6,431 people were infected and 24 deaths were recorded, according to provisional figures collected by the Healthcare and Nutrition Ministry.

However, health authorities are cautious about the drop in the number of cases reported, saying there could be a resurgence of the potentially fatal illness.

Since 1990, the incidence of the disease has increased in roughly two-year cycles, but the sudden surge, from 4,749 cases in 2003 to 15,334 in 2004, was unexpected and blamed on the emergence of a mutant, more virulent form of the virus.

Surveillance officials have found that of the four known dengue viral strains on the island, two and three have been observed to be highly active during an epidemic, causing dengue haemorrhagic fever and dengue shock syndrome.

The disease is now also more prevalent throughout the year and not restricted to biannual, post-monsoon seasonal peaks as previously observed. This suggests it is becoming endemic, said Lakmini Magodarathna, acting national coordinator for the National Dengue Control Unit.

Unlike malaria, the other mosquito-borne disease that once plagued the island's rural provinces, dengue occurs mainly in urban centres, with the capital Colombo and two neighbouring districts, Gampaha and Kalutara, topping the list. Almost half the country's 25 districts are designated high-risk areas.

"The incidence of the disease is high in places where the population density is high," said Magodarathna. But, she added, with people increasingly travelling between towns and villages and urbanisation taking place without the adequate provision of infrastructure such as sewage and rubbish disposal, dengue is beginning to appear in suburban and more remote communities as well.

Successive epidemics since the 1990s, however, mean doctors are better equipped to recognise and treat dengue, another factor in the declining death rate.

Photo: WHO

The Aedes Aegypti mosquito is the carrier of dengue fever

Public health campaign

To combat the spread of the dengue mosquito, Aedes Aegypti, health officials are advocating more public vigilance and discouraging the widespread use of insecticides administered without proper supervision. The dengue mosquito is also responsible for spreading chikungunya, characterised by high fever and inflamed joints.

Local authorities, which implement dengue control campaigns, periodically use fogging machines loaded with insecticides and petrochemicals to smoke out adult female mosquitoes, the principal carriers of the disease. However, the practice is effective only if sustained heavy doses of the insecticide are delivered.

"People should not be encouraged to use insecticides because the danger is that the mosquito will develop resistance to these chemicals," said Supriya Warusavithana of the World Health Organization (WHO). "The most effective way of preventing the disease is by cutting back mosquito breeding sites."

Besides encouraging resistant strains of both the mosquito and the virus, the pitfall of using chemicals such as malathion is that the high and frequent dosages required could lead to other diseases. The cost of funding long-term insecticide use could also prove prohibitive.

"The only way to combat dengue is to change the behaviour of people and mobilise community support to eliminate mosquito breeding sites," said Warusavithana.

The Dengue Control Unit's main strategy is persuading people to keep homes and neighbourhoods free of breeding sites, where water collects, such as tyres and other receptacles.

Home-owners, school-children and tyre traders are being targeted in a campaign to dispose of coconut shells, plastic cups, old tyres and other containers that hold even a few centimetres of water in which the mosquito can lay its eggs.

WHO has been supporting the Communication for Behavioural Impact (COMBI) strategy by providing funds and technical advice. The agency gave US$90,000 for 2008 and 2009 to supplement the government's budgetary allocation for the dengue control programme.

Although there is a legal provision to fine anyone with breeding sites on their premises, the amounts are small and insufficiently prohibitive. The government is currently drafting tougher laws to bring offenders to book.

cj/bj/mw