Brazilian researchers have shown for the first time that using Wolbachia bacteria, an experimental technique designed to shrink Aedes aegypti populations, can dramatically curb their ability to transmit Zika virus.
The team from Brazil's Fiocruz Institute reported its findings yesterday in an early online edition of Cell Host & Microbe. The results came within days of the anniversary of Brazil's first report of a human Zika infection to the World Health Organization (WHO), an event the agency highlighted today with an overview of the developments and a timeline.
Method could be used with other approaches
Wolbachia bacteria are naturally found in the gut of 60% of all insects, and infecting Aedes eggs with them was thought to shorten their lifespans, but earlier pilot projects aimed at controlling dengue revealed an extra benefit: It dramatically reduced dengue virus replication in the mosquitoes.
Wolbachia also had the same effect on chikungunya, so the new Zika finding is an encouraging sign that the control technique might be helpful for all three mosquito-borne diseases.
In March, the WHO's vector control advisory group met to discuss if any of the newer methods would be useful in battling the Zika virus outbreak and what issues might crop up if they were used. Wolbachia was one of two new methods the group recommended for carefully designed pilot deployment along with rigorous monitoring. The other was transgenic mosquitoes.
Luciano Moreira, PhD, senior author of the study, said in a Cell Press news release yesterday that the idea behind the control method has been for Wolbachia-infected mosquitoes to mate with noninfected ones and eventually replace the mosquito population with one that carries Wolbachia.
"Zika and dengue belong in the same family of viruses, so with the outbreak in Brazil, the logical idea was to test the mosquitoes carrying Wolbachia by challenging them with Zika virus and see what would happen," he said.
Researchers fed Brazilian field mosquitoes and those infected with Wolbachia human blood containing two recent Zika virus strains. After 2 weeks, they noticed that mosquitoes carrying Wolbachia had fewer viral particles in their blood and saliva. Also, the virus in mosquito saliva wasn't active—meaning they couldn't transmit the virus after biting.
"Wolbachia showed to be as effective on Zika as the most important dengue experiments we did," Moreira said.
He cautioned, however, that the strategy isn't 100% effective and won't eliminate the virus. "We know that there will not be only one solution for Zika—we have to do this alongside different approaches, like vaccines or insecticides, besides the public measures to control Aedes breeding sites."
The mechanism behind the drop in virus in mosquitoes carrying Wolbachia isn't clear, but researchers said one theory is competition for resources within cells between the bacteria and the virus that enters and wants to replicate.
WHO, CDC updates
- In its weekly situation update today the WHO said its Zika risk assessment hasn't changed, and so far it hasn't seen an overall decline in the outbreak, though levels are declining in some countries. The WHO also said incident managers from its six regional offices and headquarters are meeting in Washington, D.C., May 4 and 5 to discuss lessons learned and to coordinate the next response steps.
- The US Centers for Disease Control and Prevention (CDC) today added Peru to its level 2 travel advisory for pregnant women and those considering getting pregnant. Its advisory included a map showing which parts of Peru are above and below 6,500 feet, a level above which mosquitoes that carry Zika virus don't live.
- As of yesterday, US territories experiencing local Zika spread have reported 658 cases, most of them in Puerto Rico, the CDC said today in its weekly update. The total reflects an increase of 62 cases from the previous week, with 3 more illnesses reported in pregnant women, lifting that total to 59. On the US mainland, 472 cases have been reported in travelers, up 46 cases from the week before. Eight more Zika infections in pregnant women were reported, bringing that number to 44.
May 4 Cell Host Microbe abstract
May 5 WHO Zika 1-year overview
WHO Zika timeline