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The Directorate General of Health Services (DGHS) data show that 49 people have died of dengue, while 11, 236 people have been infected with the mosquito-borne disease so far since July this year. Globally, around 400 million people in more than 100 countries get infected with the dengue virus annually and 25,000 of them die of the disease. Dengue is endemic mostly to the low-and middle-income countries of Asia, the Pacific and Latin America. Since the bite of a particular kind of mosquito, Aedes aegypti, causes dengue fever, suppression of the mosquito population of this variety using pesticide is the accepted way to fight the disease.
One may recall at this point that spraying of pesticides to kill the larvae of Anopheles mosquito has long been in practice to eradicate malaria in this part of the world. But the problem of this method is that it cannot fully destroy the mosquitoes from their breeding ground. As a result, the mosquitoes again return and the fight to eradicate them goes on.
But recently, a biological method has been developed in the fight against dengue. In this method, the carrier of the dengue virus, Aedes aegypti, is not killed but disabled in such a way that it cannot transmit the virus to the person it bites. The common bacteria, Wolbachia pipeientis, which lives inside the cells of most of the insect species (60 per cent of them) in a biological process known as endosymbiosis (the bacterium and its host organism behave like a single organism), has proved to be a very effective agent to control the spread of dengue fever.
The question may arise whether the bacterium, Wolbachia, is safe for humans, other animals and the environment. The answer is yes. In numerous trials conducted by the World Mosquito Programme (WMP) in different countries, Wolbachia has proved to be safe for people, animals and the environment. Though the Wolbachia bacteria may live in other mosquitoes, they do not usually live in Aedes aegypti. But if Aedes aegypti is infected with Wolbachia, it becomes a powerful deterrent against the mosquito's (Aedes aegypti's) capacity for reproduction as well as its ability to transmit the dengue virus to humans through its bite. It works as a deterrent not only against dengue, but also against all other viruses, namely, Zika, chikungunya and yellow fever that Aedes aegypti carries.
How does the bacteria work to control dengue? As noted in the foregoing, Wolbachia bacteria resides inside the cells of organism acting as its host. So is also the case with Aedes aegypti once it is infected with the bacteria. And the bacteria pass from one generation of the mosquito to another through its (mosquito's) eggs. At the same time, remaining inside the mosquito cells, the bacteria compete for turf with the viruses like dengue, chikungunya, Zika and yellow fever that the mosquito also plays host to. This severely affects those viruses' ability to reproduce within the mosquito cells.
Scott O'Neil, a microbiologist at the University of Monash, Melbourne, Australia and directorof WMP has been doing his experiments with Wolbachia-modified Aedes aegypti mosquitoes since 1990s. He used the Wolbachia method in Far-north Queensland of Australia to combat dengue.
The findings are very optimistic. For it is for the first time in over 100 years, the region has become free from dengue. In another trial in 2016, a team led by him selected the city of Yogyakarta in Indonesia. The team released Wolbachia-infected Aedes mosquitoes in several areas chosen in a random fashion over a period of six months. In assessments done a few years later, it was found that the incidence of dengue fever in the areas where Wolbachia-infected mosquitoes had been released was reduced by 77 per cent compared to other areas free from such experimental mosquitoes. The result of the experiment was made public in August last year. The experimental results show the immense potential of the Wolbachia method to rid the world not only of dengue, but also of other life-threatening mosquito-borne diseases.