Aedes aegypti, the mosquito that carries the deadly dengue virus, began as a forest insect in the sub-Saharan part of Africa, but one lineage evolved to enjoy the urban environment. Transported through slave ships, these mosquitoes have traveled globally for centuries, carrying viruses like dengue. Today, dengue is recognized by the World Health Organization as a top ten global threat. Dengue infects around 390 million people and kills about 25,000 individuals annually. Dengue may be a lethal virus, but there’s a solution: Wolbachia.
The bacterium Wolbachia was discovered in 1924 in a different mosquito species, but it wasn’t until the 1980’s that scientists realized its astounding ability to spread and to control the dengue virus. Mosquitoes carrying Wolbachia can’t be infected with dengue, thus helping to prevent the spread of the deadly virus. With equal importance, Wolbachia spreads quickly among mosquitoes. It allows an insect mother containing the bacteria to produce more abundantly and pass the bacteria to her offspring. Therefore, Wolbachia is a fast and effective method of combating dengue. The bacteria is also an eco-friendly and non-toxic method of controlling dengue; it doesn’t even kill mosquitoes!
Oliver Brady, a dengue expert at the London School of Hygiene and Tropical Medicine, stated that “Wolbachia is a highly effective intervention against dengue.” To test the effectiveness of Wolbachia, the nonprofit World Mosquito Program (WMP) conducted a test in 2017 in the city of Yogyakarta, Indonesia. Researchers split the city into 24 sectors and released the carrier mosquitoes in half of them. In a year, results showed that 95 percent of Aedes aegypti mosquitoes contained Wolbachia. Starting in January 2018, fever comparisons were done between the Wolbachia and Wolbachia-free zones.
Despite the study concluding early in March 2020, due to COVID-19, enough participants were involved to make accurate conclusions about the prevalence of fever caused by dengue. Only 2.3 percent of people in the Wolbachia zones had fever-induced dengue. On the other hand, 9.4 percent of people in the Wolbachia-free zones had dengue fever --showing that Wolbachia significantly reduced the prevalence of dengue in regions where it was introduced. Researchers also discovered three important points: Wolbachia was fast moving amongst local mosquitoes, it worked against all four strains, and it lowered dengue cases by 77 percent.
While Wolbachia may have its benefits, it isn’t perfect. One problem is the amount of time it takes to develop. Aedes aegypti isn't naturally a host of Wolbachia, so the bacteria takes months to fully establish itself. Another issue is that the bacteria takes a large amount of effort to become effective. It must be present in at least 80 percent of a mosquito population to successfully take over, which can take up to 10,000 volunteers to distribute into local neighborhoods.
Experts are still uncertain if Wolbachia will be a permanent solution to control dengue, but in the meantime, the WMP plans to introduce it into more densely populated neighboring provinces of Yogyakarta, protecting 4 million people. Their efforts would annually prevent more than 10,000 cases of dengue. By 2025, the WMP aims to protect 75 million people, and by 2030, 500 million people. If successful, Wolbachia could be the key to eradicating dengue.
[Source: The Atlantic]