Eradication

Genetically modified mosquitoes

Researchers across the globe have been trying to genetically modify mosquitoes to reduce the spread of Dengue. For example, researchers at Oxford University genetically modified flightless female mosquitoes. To court males, female mosquitoes perform a flying ‘dance’, so without being able to fly, the researchers hoped that female mosquitoes wouldn’t be able to successfully breed. As well as this, lacking the ability of flight would leave female mosquitoes more vulnerable to predators. [1]

The same researchers also genetically modified male mosquitoes, leaving them sterile. These sterile mosquitoes were released in a trial in Grand Cayman to see how well it could reduce dengue. [2]

Wolbachia: the ‘mosquito vaccine’

The wolbachia method

Wolbachia is a bacteria that is carried by 60% of insect species, but does not naturally infect Mosquitoes (scientific name = Aedes aegypti) [2]. First discovered by Dr Scott O’Neill, wolbachia appears to kill the dengue virus within the mosquitoes [3]. The wolbachia method has be in development since the 90’s, and there have been various recent trials to test its ability to reduce dengue:

Scientific trials

In 2018, a study was performed in Townsville, Australia, where 4 million wolbachia-carrying mosquitoes were released. Soon after their release, the dengue rates plummeted. However, because there had been no control group in the study, the results were not reliable enough for the wolbachia technique to gain real traction. [3]

In Yogyakarta, Indonesia, a more robust trial was coordinated by ‘World Mosquito Program’, a non-profit organisation. The city, with nearly 400,000 residents, was split into 24 areas, with 12 of those receiving wolbachia-carrying mosquitoes and the other 12 left as control areas. The wolbachia mosquitoes were released in 2016 over a 6 month period. Due to the coronavirus pandemic, the study had to be cut short, and wolbachia mosquitoes were released across the city once the trial had ended. [3]

The full results have not yet been published, but the preliminary results are very promising; rates of dengue were 77% lower in areas with wolbachia mosquitoes, for several years after their initial release. Nicholas Jewell, from the London School of Hygiene and Tropical Medicine, said that the 77% estimate is likely ‘conservative’ because many people will have moved between control and non-control areas. [3]

The future of the wolbachia method

“Lançamento da Ação do Método Wolbachia. Niterói – RJ, 02/12/2019. Foto: Erasmo Salomão/MS” by Ministério da Saúde is licensed under CC BY-NC-SA 2.0

With the promising results of the Jogyakarta trial, the World Mosquito Program hopes to release wolbachia mosquitoes into areas covering 75 million at-risk inhabitants. However, they will have to first gain the support of the WHO, and source funding. 

The wolbachia mosquito releases are estimated to cost 12 to 21 US dollars per person covered. Independent economists suggest that releases of wolbachia mosquitoes will have paid for themselves within a few years. [3]

References

[1] Fu, G., et al. Female-specific flightless phenotype for mosquito control. Proceedings of the National Academy of Sciences 107, 4550–4554 (2010). doi:10.1073/pnas.1000251107 (consulted on 21 February 2021)

[2] https://www.nature.com/scitable/topicpage/controlling-dengue-outbreaks-22403714/#:~:text=Summary,Aedes%20aegypti%20lay%20their%20eggs (consulted on 21 February 2021).

[3] Guzman, M. et al (2010): “Dengue: a continuing global threat”, Nature Reviews Microbiology 8, S7-S16. Available online on https://www.nature.com/articles/nrmicro2460 (consulted on 21 February 2021).