More than half of the world’s population live in Aedes aegypti - infested areas. The global expansion of Aedes aegypti, the main mosquito species responsible for spreading dengue, chikungunya and Zika viruses, has caused an alarming increase in infections, mostly in tropical regions. Because the vaccine and treatment options are scarce and the new ones take years to develop, controlling mosquito populations in the wild has emerged as a new way of combatting mosquito-transmitted diseases.
Traditional vector control strategies include the use of pesticides and larvicides. This approach, however, has worked poorly in crowded urban areas, which are the main environment for the Aedes mosquitoes. Pesticides can be potentially harmful to humans and their long term impact is difficult to predict – mosquitoes are important elements of food chains and their elimination can disturb the environmental balance. The ideal mosquito control measure would therefore prevent virus spread but not harm the mosquito itself.
Here enters Wolbachia – a symbiotic, non-pathogenic bacterium that infects many insect species. Wolbachia does not naturally infect Aedes mosquitoes but some strains, such as Wolbachia pipientis, can be used for infection in laboratory conditions. It was shown in the past that Wolbachia-infected mosquitoes are less able to spread dengue virus. The Wolbachia-harbouring mosquito can still be infected with the virus, but will not transmit it to humans. Based on this discovery, Wolbachia-infected mosquitoes are now being released in five countries (Australia, Brazil, Colombia, Indonesia, and Vietnam) with the aim to spread Wolbachia in the wild and to reduce the occurrence of dengue outbreaks (www.eliminatedengue.com).
New evidence now suggests that Wolbachia can also limit infections with chikungunya and Zika viruses. Wolbachia pipientis, the strain that is currently being released in Colombia, can reduce the transmission potential of both chikungunya- and Zika-infected mosquitoes. In recent laboratory studies, chikungunya transmission was completely blocked and Zika-infected mosquitoes failed to transmit any virus. In addition, an independent study performed in Brazil with two currently circulating Zika isolates showed that Wolbachia-harboring mosquitoes were highly resistant to Zika infection.
With these exciting findings, the Wolbachia technology is becoming a promising eco-friendly tool to control mosquito-transmitted viruses and to supplement existing mosquito control measures.