Game changer in controlling mosquitoes
WE refer to the report “Melaka’s sterile mosquitoes method proves impotent in fight against dengue” (The Star, Oct 3; online at bit.ly/ star_sterile).
The World Health Organisation (WHO) has spearheaded a new strategic approach to re-prioritise vector control under the Global Vector Control Response, 20172030.
The new vector control responses are seen as a game changer. The Vector Control Advisory Group set up by WHO has reviewed and recommended vector control technologies using irradiation known as sterile insect technique (SIT). It uses gamma or X-ray radiation to sterilise reared male mosquitoes which are then released to mate with wild females, producing sterile eggs that are unhatchable.
Through sustained release over a period of time, the number of mosquitoes capable of transmitting the virus is thus reduced in successive generations.
The SIT is an effective biological vector control method with a strong track record of success against a range of agricultural pest insects, starting with the successful elimination of the New World screwworm (Cochliomyia hominivorax) in the United States, Central America and Libya.
The success of the technique against agricultural pest has led to increased interest in the use of SIT against public health pests, particularly the Anopheles, Culex and Aedes mosquito species.
An Italian group of researchers in 2013 released around 1,000 irradiated Aedes albopictus pupae per hectare per week, inducing up to 70%-80% sterility in target populations in three pilot sites of between 16ha and 45ha.
The current pilot field trial in Melaka, titled “Field Evaluation of Sterile Insect Technique for Aedes aegypti Suppression”, is funded by a Malaysian National Institutes of Health grant.
The field evaluation proposal was also reviewed and approved by the Health Ministry’s Medical Research Ethical Committee.
Prior to the trial, two apartment sites were selected based on the density of Aedes aegypti .In Pangsapuri Kota Laksamana, which is the treated site, the mosquito density was relatively high while Pangsapuri Taman Tasik Utama was the untreated site.
On July 15 this year, 16,000 sterile male Aedes aegypti began to be released weekly at Pangsapuri Kota Laksamana, which consisted of 13 blocks of five-storey walk-up apartments. The evaluation of the effectiveness of this approach is based on a reduction in the population of Aedes aegypti at the release site.
To date, we have conducted 13 releases of sterile male Aedes aegypti in Kota Laksamana. The monitoring to evaluate the suppression is still under progress, but initial post-release results indicate that the Aedes aegypti population was reduced by 3.37 times compared to the untreated control sites where sterile Aedes aegypti mosquitoes were not released. This shows that more sterile eggs are produced in the treated site, resulting in a reduction of the Aedes aegypti population.
In the present trial in Melaka, since the release of sterile male Aedes aegypti has been ongoing for only two and a half months, it is premature to draw any meaningful conclusion yet, although initial data is promising and encouraging.
The trial will proceed as planned to collect more field data which is essential for making a correct interpretation and coming to conclusive outcomes.