Stopping Dengue
How Scientists Managed to Prevent Its Transmission by Modifying a Mosquito
Dengue fever is a neglected tropical disease transmitted by a mosquito. It’s responsible for millions of cases every year. Although we have a novel vaccine for it, control options for dengue are limited. But in 2011, scientists were able to blockage dengue transmission in Northern Australia. They achieved it by releasing even more mosquitoes, but how?
Dengue and Wolbachia
To follow this story, we need to recognize two viruses: Dengue and Wolbachia. Dengue virus, as the name implies, is responsible for dengue fever. Symptoms may include high fever, joint pains, and skin rash. Some cases experience more severe symptoms such as bleeding and organ impairment. It is spread by the Aedes aegypti mosquito, originated in Africa, but currently is found in tropical regions throughout the world.
Wolbachia is a bacterium that is primarily found in insects. According to the CDC, six in 10 of all types of insects around the world have Wolbachia. Fortunately, it cannot make us sick. What it can do is to reduce viral replication in some insects. This indicates that when an insect is infected by Wolbachia, it becomes resistant to a group of viruses. Hence, if we can infect some Ae. aegypti mosquitos with Wolbachia, they may stop carrying the dengue virus anymore. To achieve this, we can collect every Aedes mosquito and load them with our bacteria. Clearly, it is beyond the realm of possibility. So, what these scientists did that prevented the transmission of the dengue virus in the Cairns region of Northern Australia?
Introducing Wolbachia to Ae. aegypti Mosquitos
To infect an organism with a virus without killing it, you need to have its strain, a genetic variant, or a subtype of a microorganism. Therefore, we need a strain of Wolbachia that doesn’t kill the mosquito but make it immune. It was discovered in 1997 by Min and Benzer and named as wMel. So, all we need to manage is to transfer wMel strain into Ae. aeypti. This has been achieved by O’Neill et al. but we still have a problem: We can’t infect every mosquito out there. In fact, we can!
Releasing the Wolbachia Carrying Ae. aegypti Into the Wild
There are two approaches to releasing modified insects to nature:
- Suppression approach: Reduction or eradication of natural vector populations
- Replacement approach: Replacement of natural vector populations through preventing transmission
What O’Neill et al. did in the Cairns region of Northern Australia was the replacement approach. They released the modified mosquitos every week for ten weeks and transformed the whole population of Ae. aegypti.
Conclusion
It was a remarkable success!
Since the day O’Neill released the first Wolbachia carrying mosquito in 2011, there has been no dengue transmission in the Cairns to date.
References
- Min, K. T. & Benzer, S. Wolbachia, normally a symbiont of Drosophila, can be virulent, causing degeneration and early death. Proc. Natl. Acad. Sci. U. S. A. 94, 10792–10796 (1997).
- McMeniman, C. J. et al. Stable introduction of a life-shortening Wolbachia infection into the mosquito Aedes aegypti. Science. 323, 141–144 (2009).
- Walker, T. et al. The wMel Wolbachia strain blocks dengue and invades caged Aedes aegypti populations. Nature 476, 450–455 (2011).
- Nazareth, T. et al. What happens when we modify mosquitoes for disease prevention? A systematic review. Emerg. Microbes Infect. 9, 348–365 (2020).
