Wednesday, June 27, 2007

Mosquitoes spread more than malaria

Ny Times has an article about Singapore's loosing war on their mosquitoes. Normally such stories would be about the spread of malaria, but in this case, it's about a different disease.

Mosquitoes Have the Edge in Singapore’s Dengue War

Mr. Govindarajoo is one of roughly 500 inspectors from Singapore’s National Environment Agency specially trained to conduct house-to-house search-and-destroy missions against Aedes mosquitoes, which transmit the potentially deadly dengue virus. Despite their best efforts, though, the mosquitoes appear to be winning, abetted by the boom in international travel, global warming and their own adaptability.

Singapore and its Southeast Asian neighbors are in the midst of a new epidemic of dengue (pronounced DEN-gay) that is already on course to claim more victims regionally than the last epidemic, in 2005.

Thailand has already had more than 11,000 reported cases so far this year, with 14 deaths, while 48 people have died among Malaysia’s more than 20,000 dengue cases. Sprawling Indonesia, with more than 68,000 reported cases, has had 748 deaths. And while Singapore’s two dengue-related deaths give it the lowest fatality rate in the region, its nearly 3,000 cases make its infection rate second only to Malaysia’s.

Dengue is a relative of yellow fever, hepatitis C and the West Nile virus. It infects an estimated 50 million people a year, and there remains no vaccine or treatment. In acute cases, it causes high fever and debilitating lethargy, accompanied by joint pain so intense that the disease was called “breakbone fever” when it was first diagnosed more than 300 years ago. About 1 percent of these more serious cases develop hemorrhagic fever or shock, with gastrointestinal bleeding and, in rare cases, brain hemorrhages and death.

At the moment, the mosquitoes are winning the fight, partly due to the fact that this breed of mosquitoes are more adapted to urban life than the breed of mosquitoes carrying the malaria parasite.

Aedes aegypti, the most prolific transmitter of dengue, has become ideally suited to the rapidly growing tropical urban environment. Unlike malaria-transmitting mosquitoes that stick to rural areas and swampy waters, it prefers fresh, clean water. It breeds largely indoors, needing only tiny pools of water to lay its eggs. Christina Liew, a medical entomologist at the agency, said Aedes mosquitoes are not as fussy about where they will lay eggs as was once believed. In the absence of clean water, Ms. Liew said, females will lay eggs in polluted water.

I will freely admit that I don't know anything about dengue, but the article's description of it, and the problem of creating a vaccination against it, sees rather nasty.

Dengue is an enigmatic virus, difficult to diagnose and impossible to quarantine. Ninety percent of those infected with dengue develop only mild flulike symptoms, if they feel anything at all, making them unwitting reservoirs for the virus.

Even when symptoms appear, they do so days after the patient has become infectious. And after the onset of dengue’s characteristic fever that varies widely in temperature, antibodies do not appear in significant levels for days, meaning doctors cannot use conventional blood tests to detect the virus until the worst is already over.

Creating a vaccine against dengue might be a simple matter if it were not for another quirk of the virus. Dengue has four known strains, and while infection with one strain appears to provide lifelong immunity against that strain and one of the others, it seems to make a person more likely to hemorrhage if infected with one of the other two strains. Any vaccine, therefore, would have to work simultaneously against all four strains.

Because dengue was long confined to the tropics, it remains a little-understood disease. Experts still do not know precisely how the virus affects the liver or why it causes the level of blood-clotting platelets in the bloodstream to decline.

Hopefully better research into the disease will help put an end to it.

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Blogger ERV said...

Weve gotten record amounts of rain here in Oklahoma recently. Mosquitoes are eating me and Arnie alive. Considering my recent medical fun, Im patiently waiting to get West Nile, but Ill look for these buggers too :)

btw, TAG!

June 28, 2007 3:02 AM  

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