Scientists have created mosquitoes that produce 95 percent male offspring, with the aim of helping control malaria, according to latest scientific research. Interestingly, flooding cages of normal mosquitoes with the new strain caused a shortage of females and a population crash.
The system works by shredding the X chromosome during sperm production, leaving very few X-carrying sperm to produce female embryos. In the wild, it could slash numbers of malaria-spreading mosquitoes, Nature Communications journal reveals.
Although probably several years away from field trials, other researchers say this marks an important step forward in the effort to produce a genetic control strategy.
Malaria is transmitted by mosquitoes. Despite reductions brought about by measures such as Long Lasting Insecticide Nets (LLIN) or spraying homes with insecticides, it continues to kill hundreds of thousands of people annually, mostly in sub-Saharan Africa including Nigeria.
The idea of using a “sex-distorting” genetic defect to control pest populations was proposed over 60 years ago, but this is the first time it has been practically demonstrated.
The researchers, led by Andrea Crisanti and Nikolai Windbichler of Imperial College London, transferred a gene from a slime mould into the African malaria mosquito Anopheles gambiae. This gene produces an enzyme called an “endonuclease” which chops up DNA when it recognises a particular sequence.
Crisanti said his team exploited a ‘fortuitous coincidence’: the target sequence of that endonuclease is found specifically and abundantly on the mosquito’s X chromosome. In Anopheles gambiae, all 350 copies are together, side-by-side on the X chromosome,” he told BBC News.
The research showed that when sperm are produced in mosquitoes or humans, 50 percent contain an X chromosome and 50 percent a Y chromosome. When they fuse with an egg these produce female and male embryos, respectively.
In the new mosquitoes, the X-attacking endonuclease is turned on specifically during sperm formation. As a result, the males produce almost no X-containing sperm – or female offspring. More than 95 percent of their progeny are male.
WHO and malaria
The World Health Organisation (WHO) listed Nigeria and the Democratic Republic of the Congo (DRC) as two countries that are most affected by malaria in sub-Saharan Africa.
The agency disclosed in its 2012 World malaria report that the malaria burden is concentrated in these two countries and 12 other endemic countries, which account for an estimated 80 per cent of global malaria deaths. India is the most affected country in South-East Asia.
Although it noted that 1.1 million lives were saved in the past ten years from malaria, with 58 per cent of those in high burden countries, it fears that progress made in malaria control risked being reversed if the current slash in funds dedicated to the diseases is sustained.
The report summarised information received from 99 countries with on-going transmission and other sources, and updates the analyses presented in the 2011 report.
According to the WHO, during the past decade, a concerted effort by endemic countries, donors and global malaria partners led to strengthened malaria control around the world. WHO disclosed that the scale-up of malaria prevention and control interventions had the greatest impact in countries with high malaria transmission.
It noted that after a rapid expansion between 2004 and 2009, global funding for malaria prevention and control levelled off between 2010 and 2012, and progress in the delivery of some life-saving commodities has slowed.
According to the World malaria report 2012, these developments are signs of a slowdown that could threaten to reverse the remarkable recent gains in the fight against one of the world’s leading infectious killers.
It pointed out that the number of long-lasting insecticidal nets (LLINs) delivered to endemic countries in sub-Saharan Africa dropped from a peak of 145 million in 2010 to an estimated 66 million in 2012. This means that many households will be unable to replace existing bed nets when required, exposing more people to the potentially deadly disease.
ALEXANDER CHIEJINA
