A microorganism that infects dengue mosquitoes has reduced cases of the disease by 77%, in an experiment with very encouraging results.Good news comes from the fight against mosquito-borne diseases: a large-scale dengue prevention experiment conducted in Indonesia has yielded exciting results, with a 77% reduction in cases of infection in affected areas.
All thanks to a bacterium that reduces the ability of insects to transmit dengue, and that has been spread among mosquitoes with the complicity of the citizens, involved in every phase of the trial. The test took place in the city of Yogyakarta, on the Indonesian island of Java, one of the places with the highest incidence of dengue in the world; but given its success, it could soon be extended to larger areas. The results of the study were published in the New England Journal of Medicine .
DENGUE. Dengue fever is considered by the WHO to be one of the top 10 threats to global health. It is caused by a virus spread by the bites of Aedes aegypti mosquitoes (the same ones that transmit chikungunya, Zika and yellow fever: malaria is carried by another species), which infects 390 million people every year and kills 25,000, mainly in large cities in tropical regions.
The dengue virus exists in four different “versions” or serotypes, and when you heal from one of these you are still vulnerable to the others. Not only that, in the event of a new infection, the risk of serious and fatal complications of the disease increases. This is why fighting the disease with vaccines has so far proved a very difficult challenge.
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INVISIBLE ALLY. The most effective, safe and long-lasting weapon against infection seems to be the Wolbachia bacterium , which does not harm mosquitoes but settles in the same niche usually occupied by the dengue virus, because it competes for its own resources: the harmless microorganism it greatly reduces the chances of mosquitoes becoming infected with the virus and infecting themselves, and it also makes it more difficult for the virus to replicate in infected mosquitoes.
The Wolbachia has another important feature, to be transmitted between generations, and indeed to make sure the mosquitoes that are home to have a higher reproductive success than others. Releasing a small amount of infected mosquitoes from theWolbachia in one area, in a matter of months most of the mosquitoes in the area will be immune or nearly immune to dengue – to use an analogy, it’s as if a few vaccinated could quickly lead to herd immunity.
On Wolbachia he worked for decades because before using it against dengue was necessary “convicerlo” to stably infect mosquitoes, which are not their natural hosts. Some pilot studies conducted in Australia suggested that Wolbachia could be a useful weapon against the disease, but this latest large-scale controlled trial shows that the bacterium may even be the solution to eliminate dengue from entire geographic regions.
UNEXPECTED RESULTS. Scientists from the World Mosquito Program have divided Yogyakarta into 24 zones, and periodically released Wolbachia- infected mosquitoes (five million eggs in all) in only half of them. The eggs were placed in stagnant water at every possible point, including the residents’ gardens, informed of the project with a thorough information campaign and periods of public opening of the research laboratories of entomologists. Within 9 months, 95% of the mosquitoes in the 12 tested areas harbored the bacterium. From January 2018 to March 2020, until the outbreak of the pandemic, the team tracked dengue diagnoses in every hospital or clinic in the city. Ever since the insects were releasedcases of dengue fell by 77% and hospital admissions for dengue by 86%.
WOLBACHIA TO CONQUER THE WORLD! The technique offers several advantages: once engaged, it goes on by itself, without the need for subsequent interventions; unlike insecticides, Wolbachia is not toxic to humans or mosquitoes, and insects do not develop resistance. The trial has gone so well that the next step will be releasing populations of “inhabited” mosquitoes throughout the city, with the higher goal of wiping out dengue from across the region.
The World Mosquito Program currently operates in 11 countries: today and in the coming months7 million peoplewill be covered thanks to Wolbachia , but the aim is to protect half a billion by 2030. And since the bacterium seems to work also against other infections carried by theAedes aegypti , like Zika and yellow fever, this could be the start of a real revolution in public health.
