From a political perspective and to manage public concern, fogging makes sense. It is highly visible and sends reassuring signals to the affected community that the public health authorities have the situation in hand.
Unfortunately, dozens of scientific studies looking at the effectiveness of insecticide fogging – conducted in Malaysia and overseas – indicate that the method is resource intensive but achieves little. To be effective in any given area, fogging must rapidly reduce the mosquito population by around 97 per cent and be repeated regularly.
Many infective mosquitoes escape unharmed as they are often found indoors in homes, offices and enclosed spaces when the fogging teams pass by.
A lot depends on the diligence of the human operator: machines can be poorly maintained and irregularly cleaned; insecticide dosages can be incorrect, undermining effectiveness. Fogging can also give residents a false sense of security, leading to a complacent attitude towards ensuring that drains are covered and containers are emptied of stagnant water where mosquitos breed.
Then there’s the cost. Current mosquito control efforts, mainly based around fogging operations, are extremely expensive at RM 6,700 per reported dengue case. In all, Malaysia spends around RM 310 million every year on these activities. This amount is the equivalent to the budget cuts experienced by the Ministry of Health in 2015 and 2016. Around the same amount was allocated for the 1Malaysia Supplementary Food Programme for primary school students under the 2017 Budget.
Fogging is not the only weapon in the anti-mosquito arsenal. There are a number of strategies available to reduce the breeding opportunities for mosquitos, which like to lay eggs in shallow stagnant water. Locations such as water-collecting litter, clogged drains and discarded tires are particularly favoured by these insects.
However, there are infinite numbers of such places in Malaysia. Public health authorities — even with the full cooperation of the Malaysian public — cannot hope to eliminate all breeding opportunities from the country’s parks, empty land, private houses and apartments, industry buildings, construction sites, blocked cement drains and septic tanks.
And public cooperation is challenging to secure in this gargantuan task. Health Minister Datuk Seri Dr. S. Subramaniam pointed out in 2014 that public apathy undermines effective public dengue control efforts. Few people seem willing to give up ten minutes each day to get rid of potential mosquito breeding sites around their homes and workspaces.
Even in hyper clean Singapore, practically litter-free, dengue is still a major problem: 12,000 dengue cases have been reported this year with seven lives lost.
This is not a counsel of despair. Vector control does seem to be stuck in a rut in Malaysia, but there are innovative approaches (some of which are eyebrow raising) being studied. Theoretically, mosquito numbers could be dramatically reduced by infecting the males with a fertility-reducing bacteria (Wolbachia). Trials are currently taking place in Singapore, with plans for Malaysian field tests next year. A few years ago, “genetically sterile” male Aedes aegypti mosquitoes were also released as part of viability tests aimed to decrease the population numbers of this insect. New and innovative forms of mosquito traps are also constantly being developed.
Time will tell if these innovative approaches to mosquito control will be cost-effective and scalable to the levels needed to make an impact on the disease.
But the arrival on the scene of a new preventative vaccine against dengue fever, calls into question the wisdom of pumping more money into mosquito control. This vaccine, Dengvaxia (CYD-TDV) was first licensed in Mexico in December 2015, which has now included it in their national immunisation programme.
Dengvaxia demonstrated significant levels of protection (57 per cent) against dengue infection during its clinical trials, which involved over ten thousand children in five Asian countries, including Malaysia.
The vaccine has since been licensed by nine other endemic countries including regional neighbours Singapore, Indonesia, Thailand and the Philippines. WHO has already recommended countries to adopt the vaccine in national immunization programmes, particularly for children aged between 9 and 16 years.
Deputy Health Minister Datuk Seri Dr Hilmi Yahya stated earlier this month that the government is “still doubtful of the vaccine’s effectiveness, as such there is no need to register the vaccine in the country for the time being”.
What is clear is that current approaches to mosquito control are both ineffective and costly. In light of tighter budget lines and the availability of more cost effective methods, perhaps it is time for the Ministry of Health to take on a fresh approach to fighting dengue.