January 5, 2018

Wolbachia works even better in the wild than in the lab

In a new paper published in PNAS, OUCRU researcher Lauren Carrington has provided evidence supporting the introduction of Wolbachia into areas where there are dengue virus-transmitting mosquitoes, as a biocontrol method to reduce the transmission of dengue and other arboviruses.

Wolbachia is a bacteria that manipulates its host reproductive system to enhance its spread through a population. In doing so however, it can also provide its host with other benefits, like protection from virus infections. When Aedes aegypti, the primary mosquito vector of dengue virus around the world, is infected with a strain of Wolbachia called wMel and then exposed to dengue virus, fewer mosquitoes will eventually become infected with the virus. The World Mosquito Program has been working with Wolbachia-infected Aedes aegypti for a number of years under laboratory conditions, and accumulated evidence that supports Wolbachia’s ability to reduce dengue virus transmission in the field.

This study is special though, because it directly tested whether Wolbachia would be effective at blocking dengue virus transmission from humans to mosquitoes, not just in the lab environment, but in natural conditions in the real world. To do this, Dr Carrington and colleagues collected mosquito eggs and larvae from the wild in two field sites: Nha Trang city, which was Wolbachia-free, and Tri Nguyen, a village on Hon Mieu Island (off the coast of Nha Trang). Hon Mieu is the site of Wolbachia releases for the World Mosquito Program in Vietnam. The eggs were brought back to the lab and reared under standard, optimal conditions. The oldest of the larvae that were collected, were brought back to the lab, just in time for emergence as adults. Field reared and lab-reared females were then directly fed from the blood of human dengue patients.

The team observed that, as expected, the Wolbachia-infected mosquitoes had overall reduced odds of developing a dengue virus infection in the abdomen and saliva than mosquitoes that were not infected with Wolbachia, under both field- and lab-rearing conditions. However, when wild type and Wolbachia-infected mosquitoes were reared under field conditions, the relative difference between the two groups was greater than when they were reared under laboratory conditions. This shows that lab-rearing conditions underestimate the positive effect that Wolbachia can have on preventing transmission of the dengue virus from mosquitos to humans.  Dr Carrington explained, “Our study shows that infecting mosquitos with Wolbachia is an effective way to block dengue virus transmission from humans to mosquitoes  – and the effect is even greater in the wild than in the lab”.

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