Scientists have created a new strain of mosquito they say could help in the fight against viruses such as dengue fever and perhaps even Zika.
- Wolbachia is a type of bacterium that infects mosquitoes
- Infected mosquitoes have been found to reduce the spread of dengue
- Infection with two strains of Wolbachia is even more effective at blocking dengue and could stop development of dengue resistance to Wolbachia
- Biocontrol of mosquitoes using Wolbachia could help control Zika virus
Journal PLOS Pathogens reports on the development in the lab of an Aedes aegypti strain of mosquito that has been infected with two types of Wolbachia — a bacterium that can reduce the risk of dengue spreading to humans.
The “super-infected” mosquito is more effective at blocking dengue than the singly-infected insect, co-author Professor Cameron Simmons from the Peter Doherty Institute at the University of Melbourne said.
The insect strain could also be useful in preventing the dengue virus developing resistance to Wolbachia, he added.
“It would be a higher hurdle for the virus to get over the top of,” he said.
Laboratory evidence also suggests such Wolbachia biocontrol could be useful for other viruses carried by Aedes aegypti, including Zika, chikungunya and yellow fever virus, Professor Simmons said.
In recent years, scientists have found they can limit the replication of these viruses in mosquitoes by injecting mosquitoes with a strain of Wolbachia called wMel.
Studies on dengue have shown that when a mosquito bites an infected person, the ability of the virus to spread throughout the Wolbachia-infected insect’s tissues is limited.
If no dengue virus makes it to the salivary glands of the mosquito, the insect cannot pass the virus on to humans.
We would very much like to have an insurance policy.Professor Cameron Simmons, University of Melbourne
“It’s a dead end essentially for the virus,” Professor Simmons said.
“The Wolbachia stops the mosquito being able to onward transmit the virus to a human host.”
Wolbachia is transmitted through the females to the next generation, which means the bacterial infection can spread rapidly through mosquito populations.
Concerns about resistance to Wolbachia
One of the concerns, however, is that over time, viruses will develop resistance to Wolbachia.
To reduce the chances of this, Professor Simmons and colleagues have developed a strain of Aedes aegypti that is infected with both wMel and a second strain of Wolbachia called wAlbB, which has also been shown in the lab to reduce the replication of dengue in mosquitoes.
The results of their study showed that mosquitoes that fed on blood from adult dengue patients had even less virus in their tissues than earlier strains of Wolbachia-infected mosquitoes.
Wolbachia and dengue facts
- Wolbachia is estimated to infect between 40 to 75 per cent of all insects
- The wMel strain of Wolbachia comes from a fruit fly
- The wAlbB strain comes from a species of mosquito Aedes albopictus
- Wolbachia is introduced to Aedes aegypti mosquitoes by microinjection into insect embryos
- Around 30 per cent of the world’s population is at risk from dengue fever
- There are no vaccines or drugs effective against all dengue types
- Control of mosquitoes during epidemics is considered the only option to prevent transmission
“This mosquito with the double infection has an even stronger blocking ability than the mosquito with the wMel strain,” Professor Simmons said.
He said the super-infected mosquitoes have the same ability as the singly-infected ones to rapidly spread through wild mosquito populations.
Phase III field trials of mosquitoes infected with the wMel strain of Wolbachia are set to begin in Indonesia, Vietnam and Latin America early next year.
While they began with the view of testing the effectiveness of biocontrol of dengue transmission, Professor Simmons said the trials will now also test the effectiveness against other mosquito-borne viruses, including Zika virus.
Professor Simmons said he expected viruses like Zika to be similarly vulnerable to the mosquitoes super-infected by Wolbachia.
Should resistance start to develop to the singly-infected insects down the track, researchers would then carry out trials of the super-infected insects.
“We would very much like to have an insurance policy — something in the back pocket to mitigate against the risk of dengue or zika or chikungunya, evolving resistance to the Wolbachia we have in the field at the moment,” he said.