by Lisa Winter
Over 200 million people are infected by malaria each year, and the majority of the 627,000 deaths per year are children younger than five. The disease is carried by mosquitos who act as vectors for the parasite. It’s only transmitted to humans by female mosquitoes, as they’re the only ones who bite. A team of researchers led by Andrea Crisanti of the Imperial College London managed to genetically modify mosquitos to produce 95% male offspring, eliminating mosquito populations along with the risk of malaria. The results of the study were published in Nature Communications.
In most species of mosquito, the females need a blood meal in order to acquire the nutrients to create viable eggs. When she does, she can lay about 200 eggs at a time in water, and up to 3,000 eggs over the course of her lifetime. About half of those offspring will be daughters, many of whom will live long enough to produce that amount of offspring also. For humans living near mosquitos carrying the parasite that causes malaria, those numbers of female mosquitos present a very real threat.
But what if the numbers could be skewed so that the sex ratio favors males, who are harmless to humans? This is exactly what Crisanti’s team set out to do with Anopheles gambiae, a species of mosquito endemic to sub-Saharan Africa, where 95% of malaria deaths occur. The researchers modified the males with the enzyme I-Ppol, which excises the X chromosome during spermatogenesis. This renders sperm that would produce daughters to be non-functional, while the sperm that will create male offspring are unaffected. As a result, about 95% of the resulting offspring are male.
Next, modified males were introduced to five caged wild-type populations. As the males mated with the females, they passed along the same mutation until it dominated the population. For four of the five populations, it took only six generations for the mosquitos to die out due to a lack of females.
“What is most promising about our results is that they are self-sustaining,” co-author Nikolai Windbichler said in a press release. “Once modified mosquitoes are introduced, males will start to produce mainly sons, and their sons will do the same, so essentially the mosquitoes carry out the work for us.”
This study was the first to successfully manipulate mosquito sex ratios, and it was done in a big way. The researchers hope that this information will be used to develop genetic mutations to be used in the wild, bringing large populations of mosquitos to their knees.
“The research is still in its early days, but I am really hopeful that this new approach could ultimately lead to a cheap and effective way to eliminate malaria from entire regions,” added lead author Roberto Galizi. “Our goal is to enable people to live freely without the threat of this deadly disease.”
Of course, while eradicating the mosquitos would be fantastic for eliminating the threat of malaria, what other affects would it have? Wouldn’t there be harsh consequences for the ecosystem? After all, mosquitos have been on the planet for about 100 million years and represent 3,500 species. As it turns out, mosquitos wouldn’t really be missed if they were to disappear (http://www.nature.com/news/2010/100721/pdf/466432a.pdf). While mosquitos can act as pollinators as well as a food source for other animals, their absence would be merely a temporary setback before another species filled the niche. Of course, there is a gamble in assuming the replacement organism would be harmless.
“Malaria is debilitating and often fatal and we need to find new ways of tackling it. We think our innovative approach is a huge step forward. For the very first time, we have been able to inhibit the production of female offspring in the laboratory and this provides a new means to eliminate the disease,” Crisanti explained.
Each year, sub-Saharan Africa loses about $12 billion in economic productivity due to malarial infections. Considering developed areas in these countries have per capita incomes of about US$1500, this would have very real implications for the quality of life for people in those areas. Eliminating that disease would also allow doctors and hospitals to address other health concerns, and the environment would likely benefit from not having to use insecticides.