Can we end Dengue Fever by altering mosquitoes?

Published January 01, 2009 @ 09:28PM PT

Dengue fever is a tropical virus, spread by infection-carrying mosquitoes. It’s a nasty debilitating sickness that goes after kids. It has so far been limited, as it needs a warm climate, but global warming has been expanding the dengue habitat. We've seen a steady expansion of dengue's territory since the 1980s, and a 30-fold increase in cases of dengue over the last 50 years. It has no vaccine, and no treatment beyond intravenous hydration. It kills 5% of the people it infects, and 40% of those who go untreated. Dengue is especially fatal to children under 15 years old.

So far, all attempts to develop drugs to fight Dengue have failed. Efforts have focused on developing drugs which target certain parts of the Dengue virus, killing it. They may well see success, but it will take a long time before we’ve got drugs that work.

Since Dengue is mosquito-borne, the other way to fight it is to go after the mosquitoes. Researchers in Australia are doing exactly that. They have cultured bacteria in order to inject them into mosquitoes. The bacteria then shorten the mosquitoes’ lives. A normal mosquito lives for a month; these bacteria-infected mosquitoes only live for two weeks.

And why does the mosquito’s life span matter? Because the Dengue virus takes its time maturing, and it is only infectious at the end of its cycle. Two weeks isn’t long enough for the Dengue virus to do its thing. So the mosquitoes can fly around biting everyone they want (unfortunately) and play their role in the eco-system (food for bats and frogs, mostly) but still refrain from spreading Dengue fever around. That’s pretty nifty.

If the thought of getting rid of Dengue wasn’t cool enough, here is an even better thought: malaria has a complicated life-cycle that lasts 10-18 days in the mosquito. Shorter-lived mosquitoes might well reduce the spread of malaria as well as Dengue.

If you want to do something personally to fight Dengue, you can sign up at the World Community Grid, and donate your computer’s excess computing time to developing drugs to kill the Dengue virus.

(photo credit: Gerald Yuvallos)

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Comments (7)

Is anyone working on a vaccine? If not, why not? Are there too many serotypes/subtypes? Is it not cost effective?

Something else I'd worry about is that if the mosquito's life was cut in half, then there's the serious possibility of the virus altering to adapt.

Are mosquitos, or specific types of mosquitos, primary vectors for this virus? Are they the natural reservoir for the virus? If so, any change in the virus' natural habitat will probably force an evolutionary response. Perhaps it might even find another vector if the mosquitos aren't suitable or available anymore.

Posted by Joanne Rigutto on 01/02/2009 @ 07:29AM PT
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Love the new Global Health Blog! Looks great Alanna and Change team.

kate

Posted by Kate Jongbloed on 01/02/2009 @ 12:33PM PT
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In the United States we mainly use three methods of controlling mosquitos, each effective to a degree. One is a bacteria deposited on a meal of corn husks and then spread upon the water at the laval stage. This creates a fatal case of indigestion so to speak with just the larvae. It involves no poison, and therefore is considered the safest environmentally as it's a bacteria that affects only the mosquito. The second method is a fine layer of oil. The mist only needs to be thick enough to prevent the larvae from being able to attach itself to the surface of the water with it's siphon. It shouldn't kill any fish and be completely broken within a day. The least effective is a poison mist sprayed into the air that mosquitos need to fly through. This will tend to poison any bug flying through it so it is the most environmentally dangerous method. In Latin America they are experimenting with Mosquito Fish which feed on the larvae. These fish need a tropical climate and are very effective at eliminating large infestations in stagnate water. The treatment you mentioned in Australia would seem to me to be less effective than directly killing the mosquitos, either through larvae fish or bacteria. Also, the mosquitos that would survive this long enough to breed will pass that gene on to their offspring and they tend to do this quickly. Dengue fever by the way is extremely wide spread. It's now common throughout Mexico and Latin America.

Posted by Doug Vibbert on 01/02/2009 @ 08:45PM PT
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Joanna and Doug - I also wonder how long the anti-viral effect would last. Tweaking the mosquito seems like a thrillingly high-tech solution, but is it actually a good one?

Posted by Alanna Shaikh on 01/02/2009 @ 08:55PM PT
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Hmm, looks like that's long enough for the mosquitos to reproduce, so they couldn't develope a gene for resistance. Clever indeed. When I was cave diving in Mexico a local guide mentioned all of the guide contracted had contracted the disease the month before in the Yucatan, including himself. In 1995 Mexico had 70 cases, in 2001 it had 1781, in 2007 it had 27000. Now it's starting to mutate to the hemorrhagic fever with 5000 cases in Mexico. Hemorrhagic fever is the horror movie kind, the bleeding from the eyes type that was thought to have actually wiped out over 90 percent of the population of Central America in the 1500s. I'd say the numbers of general dengue fever are vastly under reported. People in rural Mexico know there is no cure, so they don't go to the hospital and spend the money and thus they aren't counted in the official statistics.

Posted by Doug Vibbert on 01/02/2009 @ 09:06PM PT
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That's something I wondered too. OK, looking at the worst case. Millions of viruses occur with and infection and thousands of mutations. Any virus that would be transmitted with a mosquito living a shorter life span would logically be a faster growing virus. If it was transmitted to person, there would probably be fewer of the viruses as their reproduction time would be limited by the mosquitos shorter life span, and therefore less likely to create the disease. But if the disease did occur, it would be a more virulent form as it was introduced successfully by a smaller number of viruses. So the worst case, in my uneducated guess, would be a faster reproducing, more virulent
virus. Either way this virus gets my nod as the nasty boy on the block, in it's regular form it's called bone break fever because of the pain, through the internal and external bleeding into it with the hemorrhagic form and it's something that will keep me out of the jungles. We also have a far bigger human population down there then ever before due to lots of coastal tourism. Michigan anyone?

Posted by Doug Vibbert on 01/02/2009 @ 09:21PM PT
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Just did a bit more research. There are four types of Dengue fever. The problem is that if you vaccinate against just one of the forms and get bitten by a mosquito carrying a different form, there is a higher likelihood that you will then contract the hemorrhagic fever. Humans are the only vectors, it is species specific. It also appears that the four forms of Dengue have been around since they were first isolated in the 1950s.

Posted by Doug Vibbert on 01/02/2009 @ 09:41PM PT
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Author

Alanna Shaikh has spent the last ten years immersed in global health; she has worked for NGOs, companies, universities, and the US government on projects that ranged from preventing antibacterial resistance to improving maternal and child health.