There’s a bit of good news from Brazil today in the fight against Zika. A new report further confirms the ability of Wolbachia bacteria to reduce Zika virus transmission from the Aedes aegypti mosquito, the main vector at this time. Wolbachia is a bacteria that has been used for some time, especially in Australia, to control dengue.
Today’s report is the first time Wolbachia was shown to reduce Zika as well. The study* is from Brazil’s Oswaldo Cruz Foundation (Fiocruz), part of the international research collaboration Eliminate Dengue, which is centered at Monash University in Australia.
“Zika and dengue belong in the same family of viruses so with the Zika outbreak in Brazil, the logical idea was to test the mosquitoes carrying Wolbachia by challenging them with the Zika virus,” explains Dr. Luciano Moreira, senior author of the report and head of the Brazilian Eliminate Dengue team.
Drs. Scott O’Neill, right, and Luciano Moreira attending to mosquitoes in their lab - Credit... [+]
The researchers compared wild Brazilian field mosquitoes and Wolbachia-infected mosquitoes by feeding them on blood infected with strains of the Zika virus currently circulating in Brazil.
The Wolbachia-infected mosquitoes showed much lower levels of virus in their saliva. Importantly, the saliva from these Wolbachia-carrying mosquitoes did not contain infectious virus. This inhibition further suggests that this strategy may be very helpful in controlling the Zika epidemic, likely blocking Zika transmission in the field as well.
Wolbachia Blocks Currently Circulating Zika Virus Isolates - Credit Cell Host & Microbe (2016)
How does Wolbachia work?
Wolbachia works by preventing RNA arboviruses, like dengue, Chikungunya, and Zika, from replicating in the mosquito. In effect, the Wolbachia “immunizes” the mosquito against the viruses they eat with their blood meal. It’s transmitted from one generation of mosquito to the next inside the female’s egg. If a Wolbachia-infected male mates with an uninfected female, those eggs won’t hatch. If mating occurs with an infected female, normal offspring will be produced and the Wolbachia "infection" will be passed on to future generations, gradually increasing the numbers of Wolbachia-infected mosquitoes in the population. Once Wolbachia is introduced into the mosquito population, it will thus remain and be self-sustaining, so in the long term it will also be less labor-intensive than some of the other new technologies being explored.
Use of Wolbachia for a type of biological warfare is not entirely new. Using this technique, the Eliminate Dengue program has been conducting field trials to target transmission of dengue since 2011 in Brazil, Colombia, Vietnam and Indonesia, as well as the successful trials in Australia.
While I am supportive of Oxitec’s GMO mosquito technique to control mosquitoes as well, the Wolbachia have certain advantages—particularly regarding public opinion and acceptance. Many have a reflexive aversion to anything “GMO,” although the Oxitec technology appears quite safe and far safer to people and the environment than widespread pesticides.
Another advantage of Wolbachia is that it could follow any changes in the mosquito distribution; we are already seeing this with climate change and globalization having introduced the Aedes aegypti mosquito to the Americas (currently the main strain transmitting Zika).
Finally, the Eliminate Dengue program is an international, nonprofit research collaboration “supported by national governments and philanthropic donors including the Foundation for the National Institutes of Health as part of the Bill & Melinda Gates Foundation’s ‘Grand Challenges in Global Health,’ the Wellcome Trust, the Tahija Foundation and the Gillespie Family Foundation.” Professor Scott O’Neill from Monash University, the lead scientist for Eliminate Dengue, explains “Wolbachia is sustaining itself at high levels in the majority of these sites up to five years after application. In areas where mosquito populations have high levels of Wolbachia, we haven’t seen any significant local transmission of dengue.” He adds, “The method we’re using is safe for humans and the environment, and has received widespread international support from governments, regulators and community members.”
A city-wide trial of Wolbachia in Townsville, Queensland, Australia is also reporting excellent news this week, with 80% of the mosquitoes showing Wolbachia 18 months after they were first introduced into the population there.
An earlier trial in Cairns show sustained populations of Wolbachia after four years.
Students undertake mosquito release experiments as part of an applied science project (credit: Thom... [+]
One benefit of the Wolbachia project there is how it involves residents to participate in citizen science projects. Students study the mosquito life cycle and help maintain “Mozzie Boxes,” raising Wolbachia infected eggs until they mature into adult mosquitoes that then go out and breed with others, furthering the spread of the Wolbachia-infected mozzies. It’s great to see the community engagement and support of projects like the “Wolbachia Warriors program.”
This type of innovative technology will be increasingly important to the U.S. as well as Latin America because of the rapid spread of Aedes aegypti, a.k.a. the yellow fever mosquito, that is transmitting disease. As Zika spreads throughout the Western hemisphere, and we learn more about its devastating neurologic damage with microcephaly and paralysis from Guillain-Barré, we must have a greater urgency in stopping the infection.
It’s not just Zika we should prepare for. The aegypti mosquitoes can transmit dengue, Chikungunya, and deadly yellow fever, and all of these are likely to occur in the U.S. The Wolbachia technology has also been shown to reduce transmission of each of these viruses.
There is worrisome news this week as well—that Zika can infect the Aedes albopictus mosquito as well as the recent invader A. aegypti. This is important for several reasons. Aegypti is an urban dweller and can lay eggs in tiny amounts of water (even a bottle cap) in houses as well as outdoors. They are sneaky biters and attack people inside their homes. In contrast, A. albopictus can adapt to colder temperatures and survive the winters, so its range in the U.S. is much more extensive. It’s more a garden or outdoors mozzie.
Now there is some additional worry that the hardier Culex mosquito, widespread throughout the U.S. and as far north as Canada, might be able to adapt and transmit Zika. Culex already transmits West Nile, equine, and St. Louis encephalitis viruses.
Dr. Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine, put it aptly: “If that turns out to be the case, then we’re all totally screwed.”
We’re already halfway there, given that Congress won’t even bother to provide emergency Zika funding, and recessed without addressing those needs. The lack of support for public health that I addressed in my recent post is a critical mistake likely to come back and haunt us as well.
One other vitally important message from Australia is the need for extensive public education and engagement, critical to the program’s success there. O’Neill explains the elegance of the Wolbachia approach, which doesn’t involve putting toxins into the environment, as being a more natural and more targeted approach. “We’re not even trying to kill the mosquito. We’re just trying to remove its ability to transmit human pathogens.” That’s something we should have universal agreement on.
*A special thanks goes to the authors and Fiocruz team for publishing their important findings as an open access, Creative Commons licensed article, and to Eliminate Dengue for generously sharing info and images.
