Institute for Medical Research Malaysia’s Infectious Diseases Research Centre (IDRC) medical entomology unit head Dr Lee Han Lim said there was evidence that Aedes mosquitoes were becoming less susceptible to chemical insecticides because of extensive use.
“However, it is highly localised and limited to several areas only. Hence, it will not affect insecticide efficacy in other areas,” Lee told the New Straits Times.
Lee said rotating the use of insecticides that had different mechanisms of killing mosquitoes could counter the problem.
Asked if dengue strains had mutated to become a more contagious strain, IDRC virology unit research officer Dr Ravindran Thayan said there was no evidence of new dengue serotypes or genotypes.
He stressed, however, that there were possibilities of new clades (a group of organisms believed to have evolved from a common ancestor) within the same dengue genotype.
Ravindran also said the Aedes aegypti mosquitoes’ breeding habits had remain unchanged, the mosquitoes preferring to breed in still, clear and clean water.
Dr Chua Tock Hing, a professor from Universiti Malaysia Sabah (UMS), said Aedes mosquitoes were adaptable insects and able to colonise all sorts of breeding sites containing stagnant water.
Also from UMS, Dr Sylvia Daim said there was no evidence of dengue viruses mutating to become more contagious.
She said, however, that there were reports of periodical emergence of dengue viruses with new genetic types that became easily transmissible by mosquitoes and caused an outbreak under favourable conditions.
“Such events occur on a regular basis where dengue is endemic,” she said.
Dr Sylvia said organisms evolved to adapt to the changing environment and perpetuate the existence of their species.
However, micro-organisms, such as viruses, mutate much more easily and at a faster rate because of their simpler genetic machinery compared with animals and plants.
For infectious agents like dengue virus, they evolve mainly to better evade a host’s immune response and to enhance their transmissibility, she added.