Congratulations are due to Scott O’Neill and his team at the World Mosquito Program (formerly Eliminate Dengue) at Monash University for their success in eliminating dengue in Townsville, Queensland, Australia. Their approach is elegant and uses mosquitoes infected with a bacterium called Wolbachia. When these male mosquitoes mate with a female that is uninfected, the eggs don’t hatch. The method works both by reducing the mosquito population and by blocking viral replication in the mosquito.
Wolbachia naturally infects more than 60% of insects, but not the mosquito Aedes aegypti, the major transmitter of dengue, Chikungunya, and Zika.
Trials have been ongoing in Australia since 2011 as well as Indonesia, Vietnam, Columbia and, most recently, Brazil. In this latest trial, Wolbachia-infected mosquitoes were released over a 66 square kilometer area of Townsville, an area with a population of 187,000. There have been only four cases of dengue in the past four years (only one in an area where Wolbachia was established), compared to 54 in a comparable earlier period. This study was published in Gates Open Research.
Cost to establish Wolbachia in Australia was $13 per person. In Brazil or Indonesia, with their more dense population, cost is less than $3 per person. The group aims for a cost of <$1 per person.
One of the beauties of this approach is that it should be self-sustaining, as the mosquito mating will spread Wolbachia through the mosquito population, passed on between generations.
Especially given the recent outrage over Hennepin County sedating people without consent as part of a clinical trial, it is encouraging to see the efforts used in Australia and in the U.S. to get buy-in from the community for these mosquito trials.
In Australia, investigators used a “Public Acceptance Model (PAM)” with four key elements:
1) Raising awareness of their project and educating the community
2) Episodic Quantitative surveys measuring community awareness and acceptance
3) An issues management system, which quickly responded to questions from the community and provided an opt-out for direct participation
4) An independent reference and review group consisting of representatives from a variety of affected groups
Schools were also used both to educate students about mosquito life cycle, the project, and public health, and to grow and release the special mosquitoes. More than 6000 households also chose to participate in raising and releasing Wolbachia-infected mozzies.
World Mosquito Project Director, Professor Scott O’Neill stated,
“Not only were communities accepting of the technology, but they also became active participants, with residents and local school students growing and releasing their own Wolbachia mosquitoes.”
“We believe our approach will be suitable for other cities, with appropriate local adaptation, and provides a framework for scaling-up our deployment, globally.”
The World Mosquito Program group also probably has more buy-in from the community because they are a non-profit and not releasing genetically modified organisms, as well as their community engagement. The GMO issue has caused significant concern among some people, although Oxitec’s (Intrexon subsidiary) mosquito studies look very good and no significant safety concerns have emerged. Unfortunately, EPA approval is pending for Oxitec’s mosquitoes.
U.S. use of Wolbachia
MosquitoMate is conducting similar trials in Florida and has completed trials in California, New York, and Kentucky, where the company is based. In preliminary work, they have seen about an 80% reduction in biting (female) mosquitoes. Founder Stephen Dobson, PhD, believes their rate will be higher as his “ZAP”Aedes albopictus mosquitoes are dispersed over larger areas. (Their limited areas of release mean that more native mozzies are flying into these treated areas). The ZAP mosquitoes are EPA approved; a similar Aedes aegypti has an experimental use permit. They have not been looking to measure disease transmission in Florida. A variety of mosquito-borne infections occur in Florida, though at low rates.
I asked Dr. Philip Stoddard, a Florida International University biology professor and mayor of South Miami about the public’s reaction to release of Wolbachia-infected mosquitoes. He, like Dobson and the Monash team, stressed that education was the key to acceptance, and said the program was well received. Once people understood that only male mosquitoes were being released and that the males don’t bite people, they had no problem. In fact, he noted, “People were happy…unless they didn’t get them.”
*Addendum: There is a key difference in the approach of the two groups. MosquitoMate aims to suppress the mosquito population entirely, introducing only Wolbachia-infected male mosquitoes, which will have non-viable offspring. (See the YouTube above and compare to video of MosquitoMate’s approach, here). While nice for reducing human bites and disease, I have some concerns about the environmental impact. Some years ago, I visited Ding Darling National Wildlife Refuge in Sanibel, Florida, before and after the area had been sprayed to reduce mosquitoes. Not only was the mozzie population lower, but there was a dramatic decline in birds. A naturalist explained that the fish population had declined, as there wasn’t enough insect food to sustain them…and this led to the related decline in birds, who again had a much more limited food source.
In Australia, Wolbachia is introduced into both male and female mosquitoes, so they will continue to produce offspring. O’Neill explains their goal is not reduction of mosquitoes, but rather “to introduce Wolbachia into the mosquito population (by releasing male and female mosquitoes) and rely on the ability to interfere with virus replication to reduce disease transmission.”
If the success in Australia can be replicated here, use of Wolbachia will be a huge boon in the U.S., where recent years have seen an increase in dengue, Zika, and other mosquito-borne illnesses. Those are only likely to get worse with climate change and the longer, wetter summers, with increasing poverty, and with cuts to public health funding. Wolbachia could be a great addition to our armamentarium, and seems far preferable to the spraying of the pesticide Naled that was undertaken to combat Zika. Which Wolbachia approach will we use? How well will we consider the environmental impact?