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Fumigation has little or no impact on dengue transmission, say experts
By Thin Lei Win
News that the world’s first dengue vaccine efficacy trial in Thailand shows “promising” signs is especially good news for countries in Southeast Asia, where the burden of the potentially fatal mosquito-borne disease is highest.
According to the World Health Organization (WHO), of the estimated 2.5 billion people at risk globally – two-fifths of the world’s population – about 1.8 billion people live in the 10 countries that make up the Association of Southeast Asian Nations (ASEAN).
Which is why ASEAN has endorsed June 15 as Dengue Day, June being the peak dengue season for the region. Events have been planned in all the region’s countries to increase public awareness.
The potential vaccine, being developed by France's Sanofi Pasteur, is due for release in 2014.
But is it only the lack of public awareness that needs to be tackled?
Some experts say dengue’s lethal effect and spread to new areas is partly due to governments and donors neglecting the disease.
Duane Gruber, professor and director of emerging infectious diseases, at Duke-NUS Graduate Medical School in Singapore, told AlertNet “money is driving the decisions on where the priorities are for public health.”
“You have a few people in Geneva, New York and London or wherever setting the health priorities for Thailand or Indonesia,” he said. “They say, ‘Here is the money for malaria, HIV and TB,' and they’re all important diseases, don’t get me wrong, but basically resource-poor countries go where the money is.”
Every year, about 220 million people are infected with the virus and two million, mostly children, develop a severe form of the disease called dengue hemorrhagic fever. WHO estimates 21,000 die due to dengue a year.
Currently there is no cure or treatment for dengue. Part of the problem is that there are four viruses that cause the disease and a person infected by one form of the virus remains immune to that variant for life but not to the other three.
Sanofi’s potential vaccine is the first to reach the final stages of clinical development before it is introduced for human treatment.
GOVERNMENTS “FAIL”
Gruber also said the link between climate change and the increasing prevalence of dengue is overrated.
“These are climate-sensitive diseases so they are sensitive to temperature changes but… Thailand, Indonesia, Vietnam, the Philippines, all of Southeast Asia and parts of America have had ideal conditions for transmissions of dengue for hundreds of years,” he said.
“Changes of a degree or two are not going to make a difference.”
Gruber said policy makers and public health officials responsible for dengue use climate change as an excuse for failing in their job.
“We don’t have a vaccine so the only way to control it is through mosquito control,” he said.
Most countries in the world have uniformly failed in mosquito control, partly due to a lack of political will, he added.
Asian countries have been largely trying to combat dengue through insecticide fumigation, which experts say has little or no impact on transmission as it only kills adult mosquitoes and not the larvae in the breeding sites, which reach adulthood within days.
Add to this the unprecedented urbanisation and globalisation – movement of people – and one has a recipe for transporting dengue to new parts of the world.
“Basically what you have is millions of people coming to these cities living in sub-standard conditions like inadequate housing, equally large mosquito populations in those cities and every one of them has a modern airport.”
On Friday, both Gruber and Sanofi said the breakthrough in a potential dengue vaccine is a result of commitment from scientists and drug-makers. It seems that to fully control the disease will require the same input from governments.
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