Tackling the burden of dengue in Cambodia: Malaria Consortium's multifaceted approach
Dengue remains a major public health problem in Cambodia, with 14,000 cases recorded every year. When outbreaks happen, hospitals are deluged with dengue patients, reducing their capacity to respond to other diseases.
Epidemics typically occur at intervals of 5 to 7 years. The worst outbreak occurred in 2007 when 39,851 cases and 407 deaths were reported. However, it is likely that the real number of cases is much greater, with some studies suggesting that the numbers are between 4 and 30 times higher than those reported under the National Dengue Surveillance System. Dengue has now spread to rural areas, increasing the population at risk from 3.5 million to almost 11 million.
Without a cure or effective available vaccine, the most appropriate dengue control measures are vector control and the avoidance of mosquito bites. Use of insecticide is associated with a relatively high cost, and distribution methods rely on interventions such as outdoor spraying of insecticide and application of temephos (Abate®). These interventions have become less and less effective owing to the development of insecticide reactance, which has been demonstrated in several studies over the past 15 years – and this resistance is developing rapidly all over the region owing to overuse over recent decades.
There is an urgent need to identify and fund alternative cost-effective solutions for Aedes vector control that are low cost, operationally feasible, scalable and sustainable by the National Dengue Control Program – taking into account the low level of funding available to them from both internal and external funding sources.
In Cambodia, more than 80% of the Aedes mosquito breeding sites are detected in common large water jars, cement tanks and other large containers. Findings from Malaria Consortium’s large cluster randomised trial on the introduction of guppy fish – a predator of Aedes larvae – show that the number of pupae per person and adult mosquitoes in intervention villages would be significantly less than that in control areas. These studies have also found that the fish are accepted and preferred by the community to the use of Abate or other chemical insecticides, and can be easily managed by the community themselves.
Continuing this work to better design and implement effective vector control strategies across Cambodia, Malaria Consortium has recently been awarded a further opportunity to explore how a socio-ecological approach with school children could create momentum for continuous fight against dengue.
As school children, or pagoda worshippers, may be disproportionately exposed to mosquito bites owing to their higher risk of exposure to peak biting times of dengue vectors (as they are often surrounded by water jars and tanks), the project combines a health education and community participation approach to vector surveillance and control, using guppy fish distribution (as discussed above) and Autocidal Gravid Ovitraps (AGO) traps.
A simplified version of AGO traps can be produced at very low cost by the community themselves with recycled material, and, importantly, they can be used to target adult mosquitoes. Similar traps have been shown to reduce populations of adult Aedes mosquitoes by more than 80%. With these two vector control tools (guppy fish and mosquito traps) the trial will be able to target both the immature and adult stages of the mosquito.
Moreover, even though school-based health education has been shown to be an effective tool to address these gaps in engagement and understanding, such programmes have been accorded low priority so far in Cambodia. Strategies for health education are not systematically developed based on available evidence, and materials are not routinely evaluated. Given the growing evidence for its positive impact on vector control, a school-based dengue education program will be trialled in 24 schools with the Ministry of Education, and will provide the opportunity for a low-cost, integrated and locally acceptable strategy for dengue control.