THREE MILLION
Wolbachia-infected mosquitoes unleashed in seven areas, dengue cases reduced by 80%
THE government’s bid to battle dengue using Wolbachia-infected Aedes aegypti mosquitoes appears to be on the right track, with seven dengue hotspots recording an 80 per cent decrease in dengue cases.
This was the outcome of a pilot study undertaken since March 2017 in neighbourhoods in Keramat here and in Shah Alam, Selangor, where three million Wolbachia-infected Aedes aegypti mosquitoes were released.
The project aims to assess the effectiveness of using Wolbachiainfected mosquitoes to block the ability of the mosquito population to transmit dengue to human beings.
Speaking to the New Straits Times, Institute for Medical Research (IMR) director Datuk Dr Fadzilah Kamaludin said once the “invasion” of the Wolbachia-infected mosquitoes reached its peak, more than 90 per cent of dengue transmission would be interrupted.
This, she said, was observed in AU2 Keramat and Mentari Court in Shah Alam, which recorded a 77 per cent and 80 per cent reduction in dengue cases, respectively.
The results, she said, were seen in the same year the mosquitoes were first released.
Dr Fadzilah, however, said the success rate was dependent on several factors, such as the type of housing in the area they were released in and natural boundaries that impede the mosquitoes’ coverage area.
These boundaries include highways, river, vegetation, open space and industrial sites.
Dr Fadzilah said the density of Aedes mosquitoes would have an impact on the invasion of Wolbachia-infected mosquitoes on the wild population.
Asked if the Health Ministry was taking a gamble with the project as it was earlier reported that the infection could not take hold outside the 26 °C-to-37 °C bracket, Dr Fadzilah said the wAlbB (Wolbachia) strain used could withstand heat.
“A study conducted by Ross et. al. (2017) on the heat tolerance of three strains of Wolbachia — wMel, wAlbB and wMel-Pop-CLA — found that only the wAlbB strain is heat tolerant, has a high density of Wolbachia in Aedes aegypti and can transmit from mother to offspring with high reliability at 26 °C to 37 °C.”
“Studies by our collaborators indicated that this strain is tolerant to tropical temperatures. As long as the mosquito has Wolbachia, the dengue virus cannot multiply, hence transmission will be interrupted.”
She said the fiveyear research was funded by the United Kingdom-based Wellcome Trust Fund, with a grant of RM3.8 million.
Dr Fadzilah said the control method using the pathogen was effective, safe, sustainable and did not have undesirable impact on the environment.
Asked why the ministry did not go with the Toxorhynchites (a predatory jungle mosquito) instead to biologically control the menace, she said there was no evidence that the release of such mosquitoes was effective.
“Toxorhynchites is not an urban mosquito and is unlikely to survive in urban environments. Aedes aegypti, however, is highly urbanised,” she said.
On reports that the 20 to 30 per cent of the mosquito population needed to be infected to ensure the project’s success, as well as the high mortality rates involving infected young mosquitoes, Dr Fadzilah said the bacterial strain originated from “Aedes albopictus and has a low fitness cost on the mosquito”.
“This means it will not have any untoward effect on Aedes aegypti. The Wolbachia strain used in Malaysia could easily infect the wild population, achieving Wolbachia infection frequency of upwards of 95 per cent.”
She, however, cautioned that Wolbachia was not a silver bullet to combat the menace and would be integrated with the Health Ministry’s other control programmes.
The government’s unorthodox approach to tackling dengue comes at a time when the disease outbreak appears to be at its peak.
The Health Ministry on Wednesday said dengue cases had seen a 163 per cent jump this year, compared with the same period last year.