TORONTO - With at least one million people dying each year from malaria -- most of them children in sub-Saharan Africa --researchers are scrambling to find a way to stop the mosquito-borne parasitic disease by any means.
Now U.S. researchers believe they may have found one possible solution: a mosquito whose genes have been altered to render it malaria-proof.
"We basically genetically engineered in a gene that's capable of killing the malaria parasite in the mosquito's gut after it consumes the blood with the parasite in it," said principal researcher Michael Riehle, an entomologist at the University of Arizona.
"The key thing is this is the first antimalarial gene in mosquitoes," Riehle said from Tucson. "There's been other ones, but this is the first one to block it at 100 per cent."
The researchers, whose work is published in this week's issue of the journal PLoS Pathogens, created the malaria-resistant insect by re-engineering the genome of one type of Anopheles, the mosquito species responsible for transmitting the parasite between humans.
The genetic alteration boosts the ability of the bug's immune system to knock out the parasites before they can reproduce and be transmitted through the bite of a female mosquito seeking a blood meal.
"We weren't really expecting this to work quite as well as it did," said Riehle, explaining that researchers' initial aim was to affect the insect's growth rate, lifespan or susceptibility to the malaria parasite, called Plasmodium.
"So we were very pleasantly surprised."
An estimated 300 million people worldwide are infected each year with various types of Plasmodium parasites, which multiply in the liver and then infect red blood cells. Symptoms, which include fever, headache and vomiting, usually appear 10 to 15 days after a person is bitten by a mosquito.
Left untreated, malaria can quickly become life threatening by disrupting the blood supply to vital organs. The deadliest type, Plasmodium falciparum, is endemic in sub-Saharan Africa. On that continent, a child dies every 45 seconds of the disease, which accounts for 20 per cent of all childhood deaths, says the World Health Organization.
About half of the world's population is at risk for malaria, which is also a major threat in Asia and Latin America, and to a lesser extent in the Middle East and parts of Europe. In 2008, the disease was present in 108 countries and territories, the WHO says. In Canada, about 1,000 cases are reported each year, primarily people who have travelled outside the country.
While there are about a dozen different drugs used to treat malaria, in many parts of the world the parasites have developed resistance to some of them.
That's why, said Riehle, the long-term goal is to introduce malaria-proof mosquitoes into affected environments, with the hope they would eventually replace their natural cousins and halt transmission at the source.
"Our idea is to replace them instead of using insecticides to completely knock down or wipe out the population," said Riehle, noting that offspring of any surviving mosquitoes can develop resistance to those chemicals and come back stronger than ever.
But letting the genetically engineered bugs out -- they're currently housed in a high-level containment lab -- won't occur any time soon.
"It's a long ways off, probably at least 10 years or so," he said. "And the biggest reason for that is we don't have a mechanism for driving the gene through the wild population yet ... We haven't developed an efficient mechanism for giving them a fitness advantage that would allow them to out-compete the wild mosquitoes."
Riehle estimates that it would take an additional 10 years for the engineered model to completely push out existing natural species.
Ian Crandall, a malaria researcher at the University of Toronto, said going after the mosquito is "a great potential way" to try to eradicate the disease.
But he cautioned there are hurdles to overcome before a genetically altered mosquito population could be released and be "fit" enough to replace existing malaria-carrying species.
"If you start playing around with the mosquito, you run the risk that the mosquitoes you are releasing are slightly weaker," said Crandall, who was not involved in the research. "So you have to keep putting them out in the (wild) population."
"If you could successfully introduce a mosquito like this, it keys into one of the only strategies that we ever have used successfully, which is to control mosquitoes. Something that does that is likely to be far more effective for far longer than just coming up with new drugs."
Philip Awadalla, a malaria researcher at the Sainte-Justine University Hospital Research Centre in Montreal, said there's a big push on to eradicate the killer disease, including a vast research program funded by the Bill and Melinda Gates Foundation.
"When we're dealing with malaria, like many other infectious diseases, it's an arms race" between immune systems, said Awadalla. "Malaria's constantly evolving ways to evade or avoid the host immune systems -- the host being the human and the mosquito."
While Plasmodium may develop resistance over time to various drugs used for treatment, a modified mosquito may be a way of preventing the disease in the first place, he said.
"At least this is something where it's more like a pre-emptive strike."
