A team of researchers at Oxitec, based in Oxford, UK, has genetically modified male Aedes aegypti mosquitoes to produce offspring that die in the late larval stage of development. They plan to release these organisms in Malaysia to compete with wild-type mosquitoes. This effort may eventually lead to a reduction in the mosquito population, NatureNews reported.
The mosquito species, A. aegypti, is the primary vector for the virus that causes dengue fever. Over 50 million cases of dengue fever arise each year, according to the World Health Organization (WHO). By reducing the vector population, human-mosquito contact rate is lowered, thereby helping to control the spread of the disease.
The conventional Sterile Insect Technique (SIT) uses genetic modifications to induce sterility in adult mosquitoes. SIT causes lethality at a very early larval stage. This does not work well for mosquito populations due to density-dependence, according to Oxford researchers led by H. K. Phuc. Adult mosquitoes increase per capita daily egg production in response to low population density. The effects of the induced sterility are thus, counter-acted by a decrease in density-related mortality.
The new approach, termed Release of Insects carrying a Dominant Lethal (RIDL), explores a new branch of SIT for insect population control. RIDL induces late-acting lethality in mosquito larvae. The RIDL approach takes effect after the density-dependent phase is reached. Oxitec’s scientists accomplished this by inserting LA 513, a non-autonomous transposon, into the genetic code of A. aegypti embryos, according to NaureNews.
Mathematical modeling revealed that RIDL was more effective than SIT across a range of growth rate and density-dependent values. Phuc’s team of researchers found that LA 513 containing mosquitoes were not different to wild-type ones in survival or competition for mates, and lethality was 95 to 97 percent for RIDL progeny.
According to the WHO website, cases of mosquito-born dengue fever have reached unusually high rates in the past four years. Dengue primarily affects regions in south-east Asia. The disease is caused by a virus, and is marked by a sudden onset of a fever of 103-105°F, reduced blood platelets, pain behind the eyes, severe joint and muscle pains, and skin rashes. Due to the severe symptoms, dengue has been nicknamed “break-bone” fever and has the ability to cause long-term damage to blood vessels.
Since dengue is viral, there is no specific cure for the disease other than symptomatic treatments for pain management, which aren’t always readily available in rural areas of Malaysia. Dengue fever is only transmitted from vector to host, in this case mosquito to human. Hence, the control of mosquito populations is essential for control of the disease.
On May 16, Luke Alphey, founder of Oxitec and an author of the Phuc study, met with the Malaysian Academy of Sciences to begin plans for field trials for the introduction of the RIDL A. aegypti in areas with high occurrences of dengue fever, as reported by NatureNews. The authorities are reportedly satisfied with the evidence presented by Oxitec, though local environmentalists have indicated concern regarding the genetic modifications. If a general consensus is reached that any risk associated with introducing these genetically modified insects is overcome by reduction in dengue, government implementation of this plan along with the cooperation of Oxitec may occur within the month.
Further Reading and References: