Malaria-proof mosquitoes could save millions of lives

http://www.tribune.com.ng/

via Khmer NZ

Written by Sade Oguntola

Monday, 19 July 2010

Malaria, a mosquito-borne infectious disease is the fifth largest cause of death from infection in the world. Researchers working on eradidisease this disaa have developed a genetically modified mosquito which can stop the mosquito-borne parasitic spreading this disease, reports Sade Oguntola.cating this Malaria infects 250 million people a year and kills more than a million of them, mainly children, but it needs mosquitoes. In a potential step towards eradicating the disease, scientists for the first time have created a genetically modified mosquito which cannot pass malaria to humans.

The genetically altering mosquitoes was developed by University of Arizona entomologists in a way that renders them completely immune to the malaria parasite, a single-celled organism called plasmodium.

Malaria is caused by plasmodium. Only the female anopheles mosquitoes feed on blood, which they need to produce eggs. When they bite an infected human or animal, they ingest the malaria parasite. It takes one malaria parasite to infect a human and make a new malaria victim.

A person bitten by mosquito experiences symptoms, which include fever, headache and vomiting, which usually appear between 10 and 15 days.

The deadliest type of malaria is that transmitted by Plasmodium falciparum, which is endemic in sub-Saharan Africa. Left untreated, malaria can quickly become life threatening by disrupting the blood supply to vital organs such as the brain.

Current control strategies involve spraying mosquitoes with insecticides, sleeping under insecticide-treated nets or using drugs to kill the parasite once it infects humans. Unfortunately, these methods are becoming less effective as both pests evolve ways to resist the toxic treatments, so new methods to prevent malaria are sorely needed.

Artimisinin has been highly effective for treating malaria, particularly in places where resistance to other drugs has developed. But now some patients along Cambodia’s border with Thailand are taking longer to respond to the treatment.

In recent years, scientists have fiddled with the insect’s genes with hopes of developing modified mosquitoes incapable of transmitting the parasite. Although promising, these efforts produced mosquitoes with only reduced parasite transmission.

Previous attempts to create genetically modified mosquitoes have failed because although they reduced the insects’ ability to pass on the germ that causes malaria through its saliva, it was not eradicated all together.

Howevee, total blockage is very crucial. Other groups have been able to reduce the insects’ ability to pass the malaria germ between 90 and 95 per cent combining various genetic alterations, but such less-than-perfect protection could allow the germ to evolve around the mosquito’s blocking mechanism, in much the same way that drug-resistant bacteria can arise if antibiotic treatments are not completed.

For their experiments, the scientists used Anopheles stephensi, a mosquito species that is an important malaria vector throughout the Indian subcontinent.

They manipulated the mosquito’s genes, injecting new genetic information, into it and into the eggs as well. That manipulation influenced the mosquito’s life span as well as its immune response.

The mosquito’s immune system naturally destroys many malaria parasites so it stands to reason that a beefed up immune system could destroy all of the parasites. The mosquito’s digestive system could also simply consume the parasites as it digests its blood meal.

By targeting this gene, they created insects that died young so that the malaria parasite did not have the 16 days in the mosquito gut it needs to mature. Even a modest reduction in lifespan could significantly impact parasite transmission.

To test the effect of that change, researchers reporting in the journal PLoS Pathogens injected 90 of the mosquitoes with the malaria parasite. Ten days later, at a point when normal mosquitoes would have bellies full of parasites, they didn’t find a single one.

Despite this genetic engineering success, there are two main hurdles before such mosquitoes could be used to reduce malaria infections. First, the modified gene would have to multiply throughout the entire mosquito population. Usually, this would occur only if the gene can be passed down to the modified mosquitoes’ offspring - thereby making sure that the gene eventually spreads throughout the population. However, these malaria resistance genes do not have that effect.

Certainly, the process of introducing this malaria proof mosquito would need at least 10 years, in order to show concrete signs of success and ultimately end up replacing the wild mosquitoes capable of transmitting malaria parasite.

Of course, there are serious ethical concerns about releasing a genetically modified insect into the environment. Once the science is fully understood, the risks and benefits to the environment, and to human health, will have to be properly assessed.

Even so, researchers are optimistic that genetic engineering of mosquitoes and vaccines will both be important pieces of the malaria-prevention puzzle.

They suggested that a two-pronged approach that targets both disease-transmitting mosquitoes, perhaps via genetic engineering, and susceptible human populations, probably by vaccines, will probably be required for eventual eradication of this fifth largest cause of death from infection in the world.

Meanwhile, until designer mosquitoes are unleashed into the wild, there are always insecticide-laced nets that can do the job. Insecticide-treated bed nets or drugs to cure the malaria are effective ways [to prevent malaria], except resistance is developing against the parasites.