Fight dengue, a mosquito at a time
MANILA, Philippines - The word “dengue” strikes fear in the hearts of many, and with good reason: for some patients, the viral infection can be deadly.
Severe dengue affects most Asian and Latin American countries. It has put many children in these regions in hospitals or caused their deaths. There is no cure for dengue, no vaccine for this widespread disease.
Globally, dengue racked up 390 million infections last year, estimate Samir Bhatt, DPhil, and colleagues in a recent study published in the journal "Nature." This infection total is more than 3 times the dengue burden estimate of the World Health Organization.
To spread the dengue virus, you need two things: first, people who are sick with dengue; second, female Aedes aegypti mosquitoes to bite people infected with dengue and pass the virus on to other humans.
To control the spread of dengue, therefore, one must stop the virus from being transmitted between humans and insects. How? You can persuade people to wear insect repellant or to empty all containers in their homes that collect water where mosquitoes can breed. You can also use insecticides, but it would be costly.
Enter Prof. Scott O’Neill and his colleagues at the Eliminate Dengue research program. They are testing an innovative approach to control the spread of disease, after having discovered that Wolbachia bacteria inoculated to a mosquito prevents the dengue virus.
“We found that if Wolbachia were present in the mosquito, the dengue virus couldn’t grow,” O’Neill addressed in a recent forum in Manila. “If the dengue virus couldn’t grow in the mosquito, it can’t be transmitted by the mosquito.”
The research program was conducted in Monash University in Australia. Field trials began two years ago in the Cairns region.
In a nutshell, they reared mosquitoes that contain Wolbachia in the lab and released them into the site once a week. There, the mosquitoes mated with wild mosquitoes. The team then trapped these mosquitoes and took them back to the lab to determine if they had Wolbachia.
The trials were a success. “We’ve shown that when we take those mosquitoes from the field, they had Wolbachia and could no longer transmit dengue,” said O’Neill.
The trials also showed that the dengue-blocking strain of Wolbachia can easily be deployed and at very little cost. After 10 weeks of releases, the frequency of the strain was high; it continued to be higher than 95% even after releases stopped. Two years after, it stayed higher than 95% even without any additional mosquito releases.
The trials paved the way for similar tests in Brazil, China, Colombia, Indonesia, Singapore and Vietnam. O’Neill cited the following key findings:
- The technology is acceptable to the community and to regulators
- It can be easily deployed at low cost. Once established, it can be sustained.
- Lab assays showed that mosquitoes containing Wolbachia that were taken from the field have reduced capability to transmit dengue
- Mathematical modeling suggests the method “may significantly reduce and even…eliminate dengue in certain epidemiological contexts,” O’Neill said. “The likely impact of the intervention could be very large; we might see a reduction in dengue transmission in the order of 50% or greater.”
He also cited the advantages of the Wolbachia method:
1. It is natural and safe for people and the environment
Wolbachia only lives inside insect cells. It occurs naturally in up to 70% of all insect species, including mosquito species that bite people but do not transmit dengue. Wolbachia is not infectious; it cannot be transmitted to any mammals, including humans.
Regulatory bodies in Australia, the US and Vietnam have approved the Wolbachia method. “Our approach is a form of biological control that we hope will reduce our reliance on insecticide use,” said O’Neill. “The method should be particularly effective at dengue control in large urban areas of the developing world where conventional dengue control with insecticide is expensive.”
2. It requires very little resource after it has been put in place
“You do this work only once; you don’t have to keep on releasing mosquitoes,” he said. As a result, you avoid “donor fatigue” or the inability to sustain resources in a program over a long period of time.
3. It doesn’t require that people change their behaviors for the method to succeed
Getting people to take new steps — such as destroying breeding sites — can be difficult.
4. It complements other interventions
O’Neill and his colleagues are confident that their approach would be fully compatible with a vaccine for dengue fever once it is developed.
So, does the Wolbachia method curb the incidence of dengue? That remains to be seen. “Since dengue does not occur every year in the Cairns region and when it does it doesn’t always occur in the same place, the trials were not designed to directly measure reductions in dengue disease,” said O’Neill.
The method by itself may not eliminate dengue, yet O’Neill and his team hope it may be a tool that will contribute to that end. “Our big goal is to introduce Wolbachia into global Aedes aegypti populations. If we’re able to do that, I think we have the potential to have a significant impact on 390 million people, and on the annual incidence of dengue.” - Rappler.com
Dinna Louise C. Dayao is a freelance writer and editor. Her motto is, 'Saving the world from jargon and unclear language, one sentence at a time.' You can reach her at firstname.lastname@example.org.