A certain bacterium believed to prevent the spread of mosquito-borne viruses such as dengue has been found to diminish the transmission of Zika virus, Brazilian scientists revealed Wednesday.
As part of strategies to control dengue, the Wolbachia bacterium has been released in countries including Brazil, Australia, Vietnam and Indonesia. It is also found in 60 percent of common insects.
Although Wolbachia is not found among Aedes aegypti mosquitoes, the most prevalent vector for Zika virus, the bacteria can be introduced to them.
The new study, which was conducted by scientists from the Oswaldo Cruz Foundation, takes advantage of Wolbachia and injects it into female mosquitoes' eggs, which then pass the bacteria along to the offspring.
The research team divided the female A. aegypti mosquitoes into two: one group without Wolbachia, and the other group infected with it. They exposed both groups to human blood that contained Zika taken from the current outbreak.
At week one and two after exposing infected female mosquitoes to Zika, researchers used qRT-PCR to accurately measure the amount of virus in the mosquitoes' abdomens and thoraces.
The result: the Wolbachia bacteria significantly reduced the ability of infected female mosquitoes to transmit Zika and showed strong resistance to the virus.
More specifically, a week after exposure, Wolbachia-infected mosquitoes exposed to the BRPE strain of Zika saw a 100 percent reduction of the virus in their heads and 35 percent in their abdomens.
A week later, Zika levels in the Wolbachia-infected mosquitoes plummeted by 90 percent in the thoraces and 65 percent in the abdomens.
For the second Zika strain, SPH, similar results were found. One week after exposure, this strain's loads dropped by 95 percent in the head and 67 percent in the abdomens of Wolbachia-infected mosquitoes. After the second week, they were reduced by 74 percent in the head and 68 percent in the abdomen.
"The blocking effect is very [large]," says Luciano Andrade Moreira, one of the co-authors of the study.
This finding raises hopes that the bacteria could be a biological mechanism against the viral vector in the outbreak. Moreira believes infecting mosquitoes with Wolbachia could be used to reduce incidence of Zika in the wild.
"Wolbachia showed to be as effective on Zika as the most important dengue experiments we did," adds Moreira.
However, Moreira warns that the method is not 100 percent effective and is not meant to eliminate Zika. It is only part of an integrated control strategy, he says.
Entomologist Stephen Dobson, who was not part of the study, says the findings are quite encouraging. He says the advantage of the Brazilian study is that if the infection of Wolbachia is successful, there is no need to further release mosquitoes in the wild. However, the disadvantage is that it might be difficult to establish Wolbachia-infected mosquitoes in the wild as well.
Still, Dobson is optimistic. He and his team at the University of Kentucky will try to release male mosquitoes infected with Wolbachia which will mate with females.
Until an effective tool against Zika is demonstrated, Dobson says they will keep exploring options.
The findings of the Brazilian study is featured [PDF] in the journal Cell Host & Microbe.
Photo: U.S. Department of Agriculture | Flickr
