With conventional vector controlling measures against dengue- and Zika-causing Aedes aegypti mosquitoes failing, several countries have started caged and even open field trials using genetically modified mosquitoes. India has signed a Memorandum of Understanding with Monash University for using Wolbachia-infected A. aegypti mosquitoes for vector control. Dengue, Zika or chikunguya viruses cannot replicate when mosquitoes have been infected with Wolbachia bacterium; such mosquitoes cannot transmit the viruses to humans.
Researchers in Singapore have reconfirmed that Zika and chikunguya viruses have low very low ability to infect A. aegypti mosquito species that are infected with Wolbachia bacterium. Mosquitoes that were either infected or uninfected with the bacteria were then infected with Zika virus (Ugandian strain) and chikunguya virus strains. While the midgut and salivary glands of wild mosquitoes had high infection of both viruses six, nine and 13 days after infection, the mosquitoes that were infected with Wolbachia bacterium had very little of either viruses. The results were published in the journal PLOS Neglected Tropical Diseases.
Except for a couple of Wolbachia-infected mosquitoes, none of the other bacteria-infected mosquitoes had Zika and chikunguya viruses in the salivary glands at the end of 14 days after infection.
All wild mosquitoes had Zika virus in the midgut and salivary glands at all time points but nearly all mosquitoes that were infected with Wolbachia bacterium had “no detectable” virus in the salivary glands. In the midgut, the number of Zika virus in the Wolbachia-infected mosquitoes was “significantly lower” compared with wild mosquitoes.
In the case of a few Wolbachia-infected mosquitoes that had Zikia virus in the salivary glands, there were fewer number of viruses compared with wild mosquitoes.
In the case of three chikunguya strains, a fewer number of Wolbachia-infected mosquitoes were infected compared to wild mosquitoes both in the midgut and salivary glands. About 60% of Wolbachia-infected mosquitoes had chikunguya in the midgut. But only three had it in the salivary glands at day six post infection; no sampled Wolbachia-infected mosquito had any virus at day nine.
In addition to the inability of dengue, Zika or chikunguya viruses to replicate in Wolbachia-infected mosquitoes, mosquitoes infected with Wolbachia bacterium have shorter lives. When bacteria-infected male mosquitoes mate with wild female mosquitoes, the embryos fail to develop if they are males. But embryos from infected females fertilised by infected or uninfected wild males survive and this helps in sustaining the cycle.
The Oxitec technology uses male genetically modified mosquitoes to carry a dominant lethal gene. When such GM mosquitoes mate with wild female mosquitoes, the offspring die at a larval stage, well before becoming an adult mosquito. This is in part is caused by the lethal gene that produces a protein that interferes with the normal functioning of cells and prevents other genes from being switched on.