India to include bacteria in its anti-dengue arsenal

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Published: July 19, 2019 3:20:56 AM

Given Aedes aegypti—the main vector for dengue, and with Aedes albopictus, for chikungunya—is one of the few species of mosquitoes that are not naturally infected by Wolbachia, research in recent years has focused on introducing the bacteria to the mosquito in a manner that helps achieve a reduction of the vector population.

India, bacteria, anti dengue bacteria, ICMR, Indian Council of Medical Research, chikungunya, Aedes albopictus, zikaWolbachia tests are on in Colombia and Indonesia as well while the American state of Florida also sanctioned this.

India has woken up late to Wolbachia as a part of its anti-dengue/chikungunya arsenal, but the fact that the country is moving in the direction—the Indian Council of Medical Research (ICMR) is getting ready to conduct field testing of Wolbachia-infected mosquitoes—is itself quite promising. Wolbachia is a bacteria that is an obligate intercellular organisms of arthropods (the phylum in the animal kingdom to which insects, including mosquitoes, belong) that can help destabilise mosquito populations.

Given Aedes aegypti—the main vector for dengue, and with Aedes albopictus, for chikungunya—is one of the few species of mosquitoes that are not naturally infected by Wolbachia, research in recent years has focused on introducing the bacteria to the mosquito in a manner that helps achieve a reduction of the vector population. It works on multiple fronts—inside the mosquito gut, the bacteria interferes in viral replication by shortening host life-span in Aedes sp., ensuring the viral load gets limited; it also causes cytoplasmic incompatibility in an unidirectional or bidirectional manner, i.e., if an Wolbachia-infected male Aedes mosquito mates with a female mosquito carrying a different strain of Wolbachia or is uninfected, then the resulting eggs will not be viable, that is, they will produce no offsprings. The Vector Control research Centre at Puducherry has developed a Wolbachia-infected variant for India in collaboration with Monash University in the US.

Wolbachia has been demonstrated, in laboratory conditions, to be effective in malaria control also since the bacteria competes with malarial parasite in the gut of the Anopheles mosquito for nutrients, prohibiting the parasite from developing to a stage where it can cause malaria in humans once transmitted. Considering Wolbachia research has thrown up promising findings for at least a decade and a half now, it took India considerably long to wake up to its potential. Brazil, which was hit by a Zika epidemic a few years back, ran Wolbachia-mediated mosquito control tests—approved by its regulator, CTNBio—as far back as 2014, with a reported 90% fall in local wild Aedes population. Wolbachia tests are on in Colombia and Indonesia as well while the American state of Florida also sanctioned this.

Given how India saw the highest number of dengue cases in 2017 and some 9.6 million malaria cases, with over 16,000 malarial deaths, going forward with Wolbachia-mediated vector control seems a great step forward, especially since a cure or vaccine for either disease is yet to be formally announced. This becomes all the more important in light of the fact that climate change effects will cause a surge in the populations of both tropical vectors and their associated pathogens. India should also perhaps look at other vector control solutions like Oxitec’s transgenic male mosquitoes—because of the modification, offsprings from a mating of transgenic male (males are non-biting) and a wild female are unable to survive beyond the larval stage.

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