KUALA LUMPUR: Researchers recently found that dengue-spreading mosquitoes — Aedes aegypti and Aedes albopictus — have mutated to become more resilient, adaptive and virulent, causing widespread epidemics.
They said this worrying development must be factored in when devising and implementing measures to control mosquito populations.
Malaysia keeps the number of dengue fever cases managable through the heavy use of insecticides to curb mosquito populations.
However, insecticide resistance in Aedes aegypti threatens the effectiveness of the vector control tool, said a 2017 paper published in PLOS Neglected Tropical Diseases.
"Genetic mutations in these mosquitoes in response to the widespread use of insecticides are likely the cause (of their heightened resistance)," epidemiologist and health informatician Professor Datuk Dr Awang Bulgiba Awang Mahmud of Universiti Malaya said.
A 2022 study published in the Parasites & Vectors medical journal said Aedes aegypti mosquitoes were very resistant to insecticides currently in use and other solutions should be sought.
A 2021 paper in PLOS Neglected Tropical Diseases said the Aedes aegypti population in Senegal had a high metabolic resistance to widely used insecticides.
"It is only natural for simple creatures like insects, such as mosquitoes, to evolve and adapt to a changing environment," environmental health expert Professor Dr Jamal Hisham Hashim said.
"For Aedes mosquitoes, this changing environment is mainly due to urbanisation and climate change. They have adapted to breed in discarded containers, small puddles of clean water, gutters and clogged drains in urban settings."
MOSQUITO FOGGING QUESTIONED
Mosquito fogging is usually done in areas where dengue cases have been reported, to kill any adult mosquito that may be carrying the dengue virus.
While fogging would have some success in killing adult mosquitoes, experts warned that it was not enough to prevent dengue infections.
"Mosquito fogging has always been a short-term measure which targets only adult mosquitoes," said Dr Awang Bulgiba.
"It does not get rid of the larvae, nor does it get rid of mosquito breeding sites. So, while it does have its benefits, this is unsustainable nor an effective long-term vector-control strategy."
Jamal Hisham said fogging was a short-term vector-control measure to control the spread of a localised dengue outbreak.
He said destroying Aedes breeding sites and using larvicides would be a more effective strategy.
Public health expert and epidemiologist Professor Datuk Dr Lokman Hakim Sulaiman said insecticides might kill mosquitoes, but a review of the scientific literature found "no evidence that fogging works".
"I never believed that fogging was cost-effective. During my time (in office), I had even reduced fogging to once from twice for each reported case.
"To me, we continue doing it because it is the politically correct thing to do," said the former deputy health director-general.
Public health expert Datuk Dr Zainal Ariffin Omar called for a review of the policy of frequent fogging, taking into account the hazards of fogging chemicals to the environment.