A new, improved mosquito repellent on the anvil

The fight against deadly mosquito bites has got a boost, with scientists identifying three new chemicals which are safer, more effective and cheaper than the world’s commonest mosquito repellents used for the last 60 years.

The three compounds are already approved by the US Food and Drug Administration for consumption as flavour or fragrance in the food industry.

“The chemicals can be applied to bed-nets, clothes and curtains to ward off insects,” said Anandasankar Ray, an associate professor of entomology at the University of California, Riverside, who led the research team that picked the new repellent molecules after screening thousands of them.

The chemicals have the potential to replace the world’s commonest mosquito repellent DEET, which has been used for more than 60 years.

Developed by the US Army following its experience of jungle warfare during World War-II, DEET was approved for military use in 1946 and civilian use in 1957. The main ingredient of India’s commonest mosquito repellent is a compound that can be dubbed as a chemical cousin of DEET.

All three compounds are safe and mimic DEET. Repellents created using them could one day be used to prevent the transmission of deadly vector-borne diseases such as malaria, dengue, West Nile virus and yellow fever, which kill more than 10 lakh people every year.

The compounds could also fend off fruit fly (Drosophila), head lice and tribolium, or flour beetles, which are commonly found in cereal silos.

Even though some of the shortcomings of DEET, like high cost, ability to dissolve plastics and insects developing resistance, were known for years, the two main barriers in developing improved repellents were the steep costs associated with identification and the subsequent safety analyses of new chemicals. The University of California team took a different approach to bypass the expensive route. They identified a receptor and nerve cell that facilitates DEET avoidance in Drosophilla (fruit fly).

The receptor, called Ir40a, is present in neurons found in a pit-like structure in the antennae called the sacculus.

Subsequently computational methods were used to screen more than 4 lakh compounds against that olfactory avoidance receptor to pick up 100 candidate repellents.

While the researchers found a number of chemicals that ward off fruit flies and mosquitoes, three of them are considered safe in human food, report the scientists in the October 3 issue of Nature. The three compounds that mimic DEET are methyl N, N-dimethyl anthranilate, ethyl anthranilate and butyl anthranilate. More than a hundred compounds still await testing in Ray’s lab.

“We think there is incredible potential for a start-up company to develop new repellents based on Ray’s current research,” said Michael Pazzani, the vice-chancellor for research and economic development at the university.