Wolbachia pipientis is an intracellular bacteria that was first observed in the ovaries and testes of the mosquito, Culex pipiens, over 70 years ago. Recent studies have demonstrated that this bacterium is widespread among invertebrates and may naturally occur in up to 70% of all insects, including many mosquitoes. Despite this broad host range Wolbachia is not infectious and it does not infect any vertebrates, including humans.
Wolbachia’s intracellular lifestyle imposes significant limitations on its ability to spread as it can only be transmitted vertically (from parent to offspring) via cells in the female’s egg. As a result Wolbachia’s success is directly linked to the reproductive success of its insect host. Interestingly, Wolbachia maximises its own success by ensuring that infected females produce more offspring than uninfected females.
Wolbachia-infected females can mate successfully with both infected and uninfected males, however, when uninfected females mate with males infected with Wolbachia, some or all of her fertilised eggs die. This means that females infected with Wolbachia produce comparably more offspring, all of which are carrying Wolbachia. This unique reproductive advantage will effectively maintain and push Wolbachia into populations of dengue mosquitoes.
Above: Insect cell containing Wolbachia (as shown by arrows)
Our research
Our research program is investigating whether we can use Wolbachia strains that occur naturally in fruit flies to influence the ability of the mosquito Aedes aegypti to transmit dengue viruses between people.
In this project the transfer of Wolbachia to mosquitoes has been achieved using specialised microinjection techniques. Successful transfer of Wolbachia between insect species is very difficult to achieve and this was a major scientific advance.
We have recently shown that when Wolbachia is present in the mosquito it directly interferes with the ability of dengue (and other human pathogens) from growing in the mosquito and as a result from being able to be transmitted between people.
Experiments to see if Wolbachia can be transferred to humans have also been carried out and shown that this does not occur. Members of our project team have received hundreds of thousands of bites from Wolbachia infected mosquitoes over a four year period. The transmission of Wolbachia between insect species is also thought to occur very rarely in nature due to the bacteria’s intracellular lifestyle.
Wolbachia links:
www.wolbachia.sols.uq.edu.au