For the first time ever, an entire city has been protected from Dengue Fever. The Australian city of Townsville has been dengue-free since 2014, and it’s all thanks to bacteria!
I know what you’re thinking:
“Aren’t bacteria the bad guys?”
I used to think bacteria were only good for one thing, causing disease, but it turns out many bacteria are helpful, and Wolbachia takes this to a whole new level.
Wolbachia is a bacterium that is present in up to 60% of all insect species and certain strains can protect their hosts from disease, acting like an accessory to the immune system. However, Wolbachia does not naturally infect Aedes aegypti – the mosquito that spreads Dengue, Zika, and West Nile Viruses (and Malaria too!).
Dengue, West Nile, Zika and Malaria are devastating diseases that are spread from mosquitos to humans. If Wolbachia can protect mosquitos from these diseases, it’s less likely that humans will be infected.
The Wonder Woman of Bacteria
Scientists from the University of Queensland successfully transferred the wMel strain of Wolbachia into the Aedes aegypti mosquito (not an easy thing to do!). Their findings were remarkable; not only did Wolbachia protect the mosquitos from Dengue Virus, but it spread to almost 100% of the mosquito population within 30 days. This rapid transmission is due to something known as cytoplasmic incompatibility.
Put simply, if the female mosquito has Wolbachia, all the offspring will have it too. Male mosquitos are a dead end for this bacterium; if the female doesn’t have Wolbachia, the eggs won’t even hatch.
Thanks to this neat trick, you don’t need to run around injecting Wolbachia into every mosquito in town. Instead, release a proportion of Wolbachia-carrying mosquitos, then sit back as the bacteria spreads. In January 2011, that’s exactly what happened.
The Amazing Effects of Wolbachia
Releasing mosquitos to spread Wolbachia sounds like science fiction, but it was made possible by the overwhelming support of local communities.
The idea was to test the Wolbachia strategy “at home” (Australia) before moving onto countries where Dengue is endemic (e.g. Singapore). Then scientists could say “We tried this at home, it worked, and now we’re bringing it to you!”
The field tests began on home ground; in the city of Cairns, Australia. Thanks to extensive public engagement campaigns the Australian locals were enthusiastic about the project. Residents and even school students participated in releasing the mosquitos across the city.
Once Wolbachia-carrying mosquitos were successfully established in various suburbs in Cairns, the next step was to see if it could work on a city-wide scale.
In 2014, the mosquitos were released in Townsville, Australia. Fast-forward to today; the people of Townsville have been Dengue-free for 4 years!
The World Mosquito Program are now focusing on areas where Dengue, Zika and other mosquito-borne diseases are endemic.
Where there’s Science, There’s a Conspiracy Theory
Inspiration can come from the most unlikely places. In fact, I first got interested in Wolbachia after stumbling upon a blog that had some far-out conspiracy theories about Wolbachia.
The main claim was that Wolbachia was enhancing viral infection in humans, although my personal favourite was that Bill Gates is using Wolbachia to control the earth’s population.
Four papers are cited on this blog as evidence of “neutral or pro-pathogenic” effects of Wolbachia. However, simply reading these papers reveals a different story:
- Two of these papers show that Wolbachia infection has no impact of lymphatic filariasis, or Japanese encephalitis virus infection. Fair enough.
- The next paper shows that different strains of Wolbachia have different anti-viral capacities, with strains similar to mWel having the strongest anti-viral effect.
- The final paper merely shows that the wFlu strain of Wolbachia enhances infection by the avian malaria parasite in birds. However, malaria in humans is caused by a different parasite, which has been shown to be inhibited by Wolbachia infection.
To be clear, particular strains of Wolbachia (not the mWel strain used by the World Mosquito Program) can enhance infection in particulat species of mosquito.
This is precisely why research is so important – so we can get the right combination of Wolbachia and mosquito to fight disease.
So the lesson I learned today was:
“Don’t simply believe what someone tells you just because they’ve cited some papers. Read the information, and see if the results agree with the interpretation”
If you’d like to hear more about other ingenious methods of fighting infectious disease, or if you want some conspiracy theories busted, let us know!
If you’re interested in learning more about how Wolbachia is being used to fight infectious disease, check out The World Mosquito Program.
This article was first published at Public Health United.
** Congratulations to the newly-wed Mr & Mrs McAvoy **