Brazil releases Wolbachia infected mosquitoes to fight dengue

Scientists infect dengue mosquitoes with the bacteria to reduce their ability to spread the deadly virus to humans

Mosquitoes infected with a dengue-blocking bacteria called Wolbachia in Tubiacanga neighbourhood of Rio de Janeiro. Photo: AP
Mosquitoes infected with a dengue-blocking bacteria called Wolbachia in Tubiacanga neighbourhood of Rio de Janeiro. Photo: AP

New Delhi: Scientists in Brazil released a batch of mosquitoes containing bacteria that are capable of reducing the ability of mosquitoes to infect people with dengue, as part of field trials conducted among dengue-affected communities.

The Wolbachia method of eradicating dengue is being used by Eliminate Dengue, a not-for-profit international collaboration of researchers, in which Wolbachia infection is transferred to dengue causing mosquitoes. The infected mosquitoes, in turn, pass the infection on to the next generation through their eggs. Thus, these mosquitoes lose the ability to spread dengue infection to humans. This bacterium which is found in 70% of insects is not naturally present in dengue-causing mosquitoes, until scientists found a way to infect them with it. Wolbachia is harmless to humans.

In 2011 field trials in Australia, the infection was successfully transferred into Aedes aegypti mosquitoes, where it has the potential to suppress dengue and other arboviruses, and the infection was subsequently spread into two natural populations in Cairns, Queensland.

Among the supporters of the project are the Foundation for National Institute of Health, the Bill and Melinda Gates Foundation and the Brazilian government.

The researchers in Brazil plan to release Wolbachia mosquitoes in Tubiacanga field site in Rio de Janeiro once a week for three to four months, with the aim of establishing Wolbachia in the local mosquito population. The scientists in this consortium have shown that their approach reduces dengue transmission when the bacteria is introduced in mosquitoes in lab, and now are conducting field trials in Australia, Brazil, Indonesia, Vietnam, Columbia and China.

World Health Organization (WHO) estimates there may be 50-100 million dengue infections worldwide every year, while 40% of the world population are vulnerable to it. Such attempts to biologically attack the dengue-carrying mosquito are being made by other companies as well.

In April, a British biotech company, Oxitec, announced that the regulatory body in Brazil had approved the commercial release of a genetically modified mosquito which can significantly reduce the wild population of dengue mosquitoes in an area.

The Oxitec mosquito is a strain of the wild species that contains two additional genes, and is sent to mate with the wild females. Their offspring inherit the additional genes and die before becoming disease-causing adults.

Meanwhile, drugmakers including Sanofi, Takeda Pharmaceutical Co. Ltd and Merck & Co. Inc. are racing to develop the first vaccine to prevent dengue. These methods are expected to be compatible with these vaccines as they become available. After the 2011 Australia field trials, Scot O’Neill, a lead researcher of the Eliminate Dengue campaign, had noted that Wolbachia based-strategies are a new sustainable approach to dengue control, and would be particularly suited to large cities of the developing world where conventional control with insecticides is largely ineffective and prohibitively expensive.

Not all researchers are optimistic. “Mosquito eradication has been an elusive goal for the world for decades now. It is too early to say whether these strategies would have a significant impact, as what works in experimental settings may not work as well in the field,” said S. Swaminathan, professor, department of biological sciences at the Birla Institute of Technology and Science in Hyderabad. “We are not fully aware of the impact of such trials on the environment,” said Swaminathan, who has been involved in extensive research on the dengue virus in India.