Inheritable bacteria controls Aedes mosquitoes’ ability to transmit Zika.

The mosquito Aedes aegypti, typically linked with dengue fever and chikungunya transmission, is also associated with the spread of Zika virus.  In the absence of a vaccine, current effective control options are limited to reducing the abundance of mosquito vector populations. However, there is a clear need for novel efficacious approaches, given that existing strategies such as insecticides and larval biological control have proven unsustainable and ineffective at halting Zika disease spread.  Now, a study from researchers at Oswaldo Cruz Foundation (FIOCRUZ) shows that Aedes mosquitoes carrying the bacterium Wolbachia are drastically less able to transmit Zika virus.  The team state that their data indicates the use of Wolbachia-harboring mosquitoes could represent an effective mechanism to reduce Zika virus transmission and should be included as part of Zika control strategies.  The opensource study is published in the journal Cell Host & Microbe.

Previous studies show the Wolbachia bacteria were first identified in 2005 as a way to combat mosquito-borne infections. After four years, researchers were successful in their attempts to isolate the bacterium from fruit flies and inserting it into Aedes mosquitoes’ eggs without using any genetic alteration. They expected Wolbachia to shorten mosquitoes’ lifespans, however, the bacterium provided an added bonus, in that it heavily reduced the Dengue virus replication in the mosquito.  The same effect was previously seen on Chikungunya virus, also transmitted by Aedes mosquitoes.  Originally inserted into Aedes eggs as part of the Eliminate Dengue Program, the bacterium is passed on from mother mosquitoes to offspring, so it is a sustainable control agent.  The current study investigates mosquitoes carrying Wolbachia challenged with Zika virus.

The current study observed Brazilian field mosquitoes and Wolbachia-infected mosquitoes Zika fed with human blood infected by two recent strains of the Zika virus currently circulating in Brazil. Results show that after two weeks, the mosquitoes carrying Wolbachia had fewer viral particles in their bodies and saliva. Data findings show that the virus present in the mosquito saliva was not active, meaning, after biting, the mosquito would not be able to transmit Zika virus.

The group state that the reason for this drop in viral reproduction is presently unknown, however, one theory is because Wolbachia lives inside of the mosquito’s cells, once the virus enters the cell to replicate, there is an internal competition for resources. They go on to note that this drop held true no matter how many Wolbachia the mosquito carried.

The team surmise their findings show that Wolbachia is effective as a vector control against Zika. The go on to caution that the strategy is not 100% effective nor will it eliminate the virus, as it is known there will not be one solution for Zika and predict different approaches, like vaccines or insecticides, besides the public measures to control Aedes breeding sites.  For the future, the researchers are discussing the Wolbachia approach with the Brazilian Ministry of Health, hoping to raise the resources and public support to test its effect on Zika in the field.

Source: Oswaldo Cruz Foundation (FIOCRUZ)