- by Alison Booth

Wolbachia programs in Asia: different approaches to fighting dengue

In the first article in our two-part series on Wolbachia, we looked at how Wolbachia-infected mosquitoes hold the key to reducing dengue outbreaks. In fact, an increasing number of communities across Asia are embarking on Wolbachia programs. In this second article, we compare the differences and similarities between Asia’s Wolbachia programs.

The number of Wolbachia programs across the world is growing rapidly – across Asia in particular. Countries are taking different approaches to Wolbachia: some release both male and female mosquitoes infected with Wolbachia, while others release only males.

The World Mosquito Program (formerly Eliminate Dengue) has released both male and female Wolbachia-infected Aedes mosquitoes in Vietnam, Malaysia, and Australia. This ‘replacement’ approach aims to grow the percentage of Wolbachia-infected mosquitoes until the population is high enough to sustain itself without further releases. The program explains:

“The World Mosquito Program’s Wolbachia method is unique because it is self-sustaining and does not need to be continually reapplied, making it an affordable, self-sustaining, long-term solution. Our method reduces the ability of mosquitoes to transmit dengue, Zika, and chikungunya on to people, without suppressing mosquito populations and potentially affecting ecosystems.”

These Wolbachia programs release the infected mosquitoes in two different ways: either releasing adults from public areas near homes or placing mosquito release containers on residents’ properties. These containers hold mosquito eggs. The eggs hatch and develop into adult Wolbachia mosquitoes over a two-week period, then fly into the environment to breed with wild mosquitoes.

An alternative approach

The Verily (the life sciences arm of Google’s parent company Alphabet) ‘Debug’ Wolbachia program, on the other hand, is only releasing male Wolbachia-infected Aedes in its California intervention, again over a period of weeks. When the males (bred from MosquitoMate’s Wolbachia-infected mosquitoes) mate with wild females, the eggs produced won’t hatch, ‘suppressing’ rather than ‘replacing’ the mosquito population in the region.

“After receiving official and community approval we will begin releases of sterile males to show that we can significantly reduce or possibly eliminate the local population of Aedes aegypti mosquitoes.”

However, the World Mosquito Program argues that a suppression approach “requires the release of a large number of male mosquitoes to reduce the overall mosquito population. As with insecticides, this technique would need to be reapplied over time as the population of mosquitoes gradually returns.”

Nevertheless, Verily is not the only company exploring using ‘sterilised male mosquitoes’ to suppress Aedes populations. The Bill and Melinda Gates Foundation is also exploring a similar idea, working with UK-based Oxitec developing genetically modified male ‘friendly mosquitoes‘ whose offspring should in theory never reach maturity. Incidentally, The Bill & Melinda Gates Foundation is also working with the World Mosquito Program.

Wolbachia programs in Asia

As we speak, interest in Wolbachia-based dengue interventions is growing across Asia. In Cambodia, India and Sri Lanka, local authorities are holding discussions with the World Mosquito Program, exploring options for using Wolbachia-based Aedes as a new tool in their fight against the dengue alongside other viruses, including Zika. Discussions are also underway in the Pacific Islands of Fiji, Kiribati, Vanuatu and New Caledonia.

Meanwhile, the World Mosquito Program continues to release both genders of mosquito while optimising its strategies around the choice of the Wolbachia bacteria strain in Australia, Indonesia, and Vietnam. According to the World Mosquito Program website:

  • In Australia, Wolbachia is still self-sustaining in northern Queensland after six years, with no evidence of local spread of dengue in those areas.
  • Trial releases began in Indonesia in January 2014. Further trials are helping the program develop its method for large-scale, low-cost releases of Wolbachia mosquitoes across entire cities.
  • Vietnam first released Wolbachia mosquitoes in a trial in 2013. After early successes, trials were expanded to more locations and continue today.

Outside of the World Mosquito Program, China, Malaysia and Singapore are also embarking on Wolbachia programs as part of their fight against dengue:

  • A project from the Sun Yat-Sen-Michigan State University Joint Center for Vector Control for Tropical Disease is releasing male Wolbachia mosquitoes in China.
  • In Malaysia, the Health Ministry announced in March that its Institute for Medical Research released 16,000 male and female Wolbachia-infected mosquitoes.
  • Singapore is carrying out a small-scale study to explore using Wolbachia-carrying Aedes males on the recommendation of its National Environment Agency’s Dengue Expert Advisory Panel. The suppression strategy is in line with Singapore’s goal to eradicate the mosquito.

Community engagement

While approaches may differ across Wolbachia programs in Asia, there are also some distinct similarities between them: the local community always plays a key role in their success, in particular. After all, the programs are releasing the Wolbachia-infected mosquitoes into people’s backyards.

Image from one of the Wolbachia programs in Asia of a woman in Indonesia being shown the variety of mosquitoes caught during a monitoring program.

A member of the World Mosquito Program team in Indonesia shows a resident the different mosquito species caught in a mosquito monitoring trap. Image via World Mosquito Program

A study into the risks associated with Wolbachia releases highlighted how releasing mosquitoes affects communities around the release sites and that interventions must involve communities throughout the process. If the community is not engaged adequately from the outset, it could lead to community opposition and prevent releases. Wolbachia programs in Asia should, therefore, develop a communication strategy tailored to the local community, listening to and addressing community concerns.

Read more about how Wolbachia-infected mosquitoes are reducing dengue outbreaks.

The World Mosquito Program’s teams work with community leaders and residents in each of its projects. In Indonesia, for example, the team “spent many months talking with community leaders and residents at the district, village and hamlet levels to gauge support before releasing Wolbachia mosquitoes.” Meanwhile, the Singapore NEA has a Wolbachia FAQ webpage with answers to specific questions and webchat where people can ask any others.

The community isn’t just the key to ensuring programs go ahead; it also plays a vital role in actually releasing the Wolbachia-infected mosquitoes. In Australia, for example, Eliminate Dengue developed an educational program called Wolbachia Warriors that allows school children to take part in the releases. In Indonesia, the community held a release ceremony to launch the field trials.

As the number of Wolbachia programs increases across the globe, we want to hear your stories about your local program.

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