KUALA LUMPUR: MALAYSIA’S long battle with dengue may show some sign of relief with the Health Ministry ’s release of Aedes mosquitoes infected with the Wolbachia bacteria.
Health director-general Datuk Dr Noor Hisham Abdullah said the Institute for Medical Research’s (IMR) pilot project involving the release of the infected vector in Shah Alam and Keramat two years ago had begun to show encouraging signs.
This came at a crucial time because as at Feb 23, there was a 163 per cent jump in dengue cases compared with the same period last year.
Dr Noor Hisham said the ministry recorded 23,914 cases within the timeframe, an increase of 14,843 cases compared with the same period last year.
“Dengue fever has claimed 40 lives as at Feb 23, a 100 per cent increase in deaths compared with the same period in 2018.
“Even though the increase in deaths due to dengue is also seen in other countries in the region, the dengue situation is still troubling.”
He said this while drawing on a briefing carried out by the ministry ’s Disease Control Division’s senior principal assistant director, Dr Rahmat Dapari, on the release of the infected vector to replace local populations of Aedes mosquitoes. The project was implemented so that infected mosquitoes cannot spread dengue, Zika and Chikungunya.
“These mosquitoes are infected with Wolbachia bacteria, which is naturally present in around 60 per cent of insects.
“Wolbachia also causes aedes mosquitoes to be free of the dengue virus so they can’t spread it,” said Dr Noor Hisham.
Universiti Kebangsaan Malaysia’s parasitology and entomology expert, Associate Professor Dr Hidayatulfathi Othman, said she was heartened by the positive signs showed by the pilot project as previous efforts to control the population of Aedes mosquitoes, including releasing genetically modified ones, were unsuccessful.
She drew on the release of genetically-modified mosquitoes, a plan that the government had abandoned due to costs and lack of studies.
Hidayatulfathi said while Wolbachia was naturally occurring in most insects, it was not the case for Aedes aegypti mosquitoes.
“The bacteria arrests the development of the virus causing dengue and Chikungunya. Those with Wolbachia cannot transmit dengue when they bite people,” she told the New Straits Times.
She said male mosquitoes infected with the strain that were released into the wild would mate with females, but would not produce offspring.
“Infected females will produce hatchlings, but their larvae will no longer be vectors. So this is a great move, but they have to release at least 20,000 to 50,000 in one go.”
She said the mosquitoes needed to be released in many areas to gauge its efficacy.
She said it was better to release the insects in neighbourhoods that were partially cut off from others so the mosquitoes cannot move to other places.
“For example, Shah Alam is a good place to do so, while Keramat is open and is well-connected to other places, which may have an effect on how the mosquitoes adapt to the area. This affects the way the authorities study the effectiveness of the project later.”
She said IMR needed to identify the most suitable strain of the bacteria so that it produced the best results.
“There are many strains, so it must be very careful in its selection. Some can withstand our climate, but cannot fully curb the development of the virus.”
The bacteria has many strains, and it can only take hold of the vector (mosquitoes) in temperatures outside the 26°C to 37 °C bracket. Those infected within the temperature range can still lay eggs that hatch into mosquitoes that can transmit dengue.
There is also the issue of high mortality rates among young mosquitoes that are infected.
Twenty to 30 per cent of the mosquito population in an area also needs to be infected for the bacteria to take hold and push down dengue rates.
Dr Hidayatulfathi said the government should not abandon awareness programmes as human activity had been identified as the main factor behind mosquitoes breeding at alarming rates.
“Malaysians think that combating dengue is only the government’s job, not theirs. They wash their hands off at the point of paying taxes. When the council comes to fog their neighbourhoods, they don’t even open their doors.