Delhi: To tackle dengue, MCDs explore an unlikely ally - bacteria
The key to fighting outbreaks of dengue – an annual public health problem for Delhi – may lie in a bacterium found in large swathes of the world’s insect population.
With Delhi emerging from its second-worst dengue outbreak last year, the city’s municipal corporations are now planning to carry out a pilot project to deploy Walbochia bacteria to reduce the transmissibility of vector-borne diseases.
Dismayed by the public health response to the outbreak, the Delhi high court last month ordered the constitution of a task force headed by commissioners of the city’s three civic bodies to take steps to prevent the Capital from “being infested by mosquitoes”.
A senior public health official, who is part of deliberations in the task force, said the local bodies are now planning to deploy Wolbachia bacteria to reduce the spread of dengue during the next annual cycle. Wolbachia is a common bacterium that infects insect species, and in turn, in the case of mosquitoes, prevents them from being infected by (and hence spreading) dengue infections.
“The studies on reducing the transmissibility of dengue and chikungunya from aedes aegypti mosquitoes by using the Wolbachia bacteria have shown positive results in countries like Indonesia and Brazil. Similar projects are being carried out in Puducherry’s Vector Control Research Centre (VCRC) from where we plan to seek help. In this method, the mosquitoes are infected by naturally occurring Wolbachia bacteria which results in reduction of dengue virus transmissibility,” the official said, asking not to be named.
Delhi recorded 9,613 dengue cases and 23 fatalities due to the infection last year, the latest data from the three municipal corporations shows. The caseload and death toll in 2021 was the highest in the city since the 2015 outbreak that left nearly 16,000 infected and killed at least 60.
Multiple research projects have shown that mosquitoes infected by the Wolbachia bacterium don’t transmit dengue, since the replication of the virus is halted.
“If a sufficiently large population of mosquitoes is multiplied in the environment, dengue transmission in a given area can possibly be halted. Studies in Indonesia have indicated a 77% drop in cases,” the official quoted above added.
The Wolbachia bacterium has been found to occur naturally in 60% of the world’s insect species. While the dengue-causing aedes aegypti mosquito is not one of these species, scientists have, over the years, been able to transfer it into the breed by injecting it into mosquito eggs.
A 2020 study published in The Lancet Infectious Diseases journal titled “Wolbachia, a bacterium fighting on our side” said risk have concluded that the bacteria is safe and does not cause any documented harm to human beings. The World Mosquito Program is overseeing disease control efforts using Wolbachia.
The Lancet review states that the results have been encouraging. “In Vinh Luong in Vietnam where the releases were completed in 2018 over an area of 2.2 square kilometres, there has been a reduction in dengue incidence of 86%, compared to a neighbouring city with no release of mosquitoes. In Yogyakarta in Indonesia--the site of the first randomised controlled trial involving wolbachia-- a pilot study found that dengue incidence dropped by 76% in the areas where the infected mosquitoes were released,” the study highlights.
The approach has been developed by Monash University in Australia while field trials have been carried out in multiple cities.
Dr. C. Sadanandane, a consultant at the Indian Council of Medical Research (ICMR) - Vector Control Research Centre in Puducherry said local strains have been developed by the centre’s researchers from the original strain from Australia. The next, he said, will be field trials to check its efficacy.
“We will be able to know the efficacy of the method locally only after the field trials in India. We received the strain from Monash University, from which our own local strain has been developed. We are looking after the colony of Wolbachia laden mosquitoes and it may take some more time to carry out field trials,” he added. In 2017, ICMR signed an agreement with Monash University to work on this method in India.