Certain vector-borne diseases including Chikungunya, dengue and Zika are rising public health challenges in Southeast Asia. This programme investigated ways to improve vector control by engaging and educating local communities and using innovative technologies such as the sterile insect technique.
Project 1. Impact of socio-ecological systems and resilience-based strategies on dengue vector control in schools and neighbouring household community in Cambodia (led by Drs Leo Braack and Jeffrey Hii, Malaria Consortium Asia, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand)
Project 2. Innovative vector birth control and socio-ecological strategies for the prevention of dengue, Chikungunya and Zika disease in Bangkok (led by Dr Pattamaporn Kittayaporn, Centre of Excellence for Vectors and Vector-Borne Diseases, Faculty of Science, Mahidol University at Salaya, Thailand)
Dengue is the most rapidly spreading mosquito-borne viral disease in the world and Asia records about 70% of the global dengue cases (>390 million p.a.). Dengue is transmitted by Aedes mosquitoes, through a bite from infected female Aedes aegypti. These mosquitoes also transmit other viruses including chikungunya and Zika. There is no practical vaccine and there are no specific treatment drugs for dengue, so control measures are largely focused on reducing the mosquito populations. However, Southeast Asia is seeing a rise in cases of insecticide resistance. This means that the current methods of reducing the mosquito populations –spraying the inside of homes with insecticides (indoor residual spraying) and coating mosquito nets with insecticides (long-lasting insecticidal nets) –are not proving as effective in killing mosquitoes. Therefore, there is value in research for alternative methods for mosquito control.
What is the dengue situation in Cambodia?
“Over the last few years it’s been increasing in significance. And I believe the lack of integration regarding public health interventions targeting dengue has not accentuated, and has not necessarily helped in addressing the problem, at least in its sustainable dimension.”- Dr Pierre Echaubard, Co-Investigator SESR-based strategies in Cambodia.
“It affects the whole family, the whole community and the rest of society.” - Dr Chea Thy, Co-Investigator, SESR-based strategies in Cambodia; and, Manager, Dengue Vector Control Programme, Phnom Penh, Cambodia
What is the dengue situation in Thailand?
“This year (2019) we have double the number of cases compared to last year.” - Dr Pattamaporn Kittayapong, PI, SIT Project; and, Professor, Center of Excellence for Vectors and Vector-Borne Diseases, Mahidol University, Thailand.
“Dengue is a very serious problem in Thailand. Every year we have almost 100,000 cases per year and almost 100 cases die every year.’- Dr Darin Areechockchai, Epidemiologist and Deputy Director of the Division of Vector-Borne Diseases, Ministry of Public Health, Thailand.
So, what are researchers trying to do?
Globally, researchers are studying different ways of lowering the numbers of mosquitoes that transmit dengue. The Special Programme for Research and Training in Tropical Diseases (TDR), housed at the World Health Organization (WHO), provides technical and funding supports for these studies. One of the two projects in this specific programme focuses on increasing community awareness and engagement, and on simple vector control tools that can be used by communities themselves, such as mosquito traps, mosquito larvae-feeding guppy fish, and clearing their surroundings of containers that mosquitoes can breed in. The second approach uses sophisticated laboratory techniques that sterilize mosquitoes and prevent them from transmitting dengue. These techniques involve a bacteria (Wolbachia) and radiation.
1 . Dengue vector control in Cambodia: Socio-ecological strategies in schools and communities.
This project, based in Cambodia, is using very simple methods to try to lower mosquito numbers, in addition to the established strategies by the national dengue control programme. This involves a high degree of community involvement –including making the mosquito traps, breeding and rearing guppy fish that feed on mosquito larvae in water storage jars, and cleaning surroundings. Lessons on dengue are also being integrated into the primary school curriculum, and students, teachers and health workers are being trained to continue spreading awareness on mosquito control.
In what way is this socially innovative?
“This particular method is a more voluntary, co-opting method that will hopefully get greater responsibility … It’s not a top-down approach; it’s showing people how they can actually, with very limited resources, how they can help themselves.”- Dr Leo Braack, Co-PI SESR-based strategies in Cambodia; and, Senior Vector Control Specialist, Malaria Consortium-Asia.
2. Vector birth control in Southeast Asia
The technique combines two ways of sterilization to create laboratory-bred super-sterile male mosquitoes: Wolbachia and radiation.
Wolbachia is a bacteria that occurs naturally in 40% of insect species but is not found in Ae. aegypti. When inserted into Ae. aegypti, it does something strange – it prevents the mosquitoes from spreading dengue. It also does something else – it moves into the reproductive system and sterilizes male mosquitoes. When wild female mosquitoes mate with males that have Wolbachia, the females lay eggs that do not hatch. The researchers used this Wolbachia method, but they wanted to make sure the mosquitoes that they release are super-sterile. To do this, they did an additional step. They took all the male mosquitoes infected with Wolbachia and sterilized them using radiation. These super-sterile male mosquitoes were then released into the environment, to mate with wild females that would then lay eggs that do not hatch.
The pilot study was carried out in a semi-rural village in Chachoengsao Province in eastern Thailand. The next phase of the research is planned to take place in Bangkok – a disease-endemic location, which is also a tourist hotspot, from where it is easy for diseases to spread globally.
Suggested reading
Echaubard P, C Thy, S Sokha, Set Srun, C Nieto-Sanchez, KP Grietens, NR Juban, J Mier-Alpano, S Deacosta, M Sami, L Braack, B Ramirez, J Hii. 2020. Fostering social innovation and building adaptive capacity for dengue control in Cambodia: a case study. Infectious Diseases of Poverty. 9:126. doi: 10.1186/s40249-020-00734-y
Kittayapong P, S Ninphanomchai, W Limohpasmanee, C Chansang, U Chansang, P Mongkalangoon. 2019. Combined sterile insect technique and incompatible insect technique: the first proof-of-concept to suppress Aedes aegypti vector populations in semi-rural settings in Thailand. PLOS Neglected Tropical Diseases. 13(10):e0007771. doi: 10.1371/journal.pntd.0007771.
Collaborators: Malaria Consortium, Centre Cambodia National Malariology/Ministry of Public Health, Cambodia Ministry of Education, Bournemouth University UK, Global Health Group International, Institute of Tropical Medicine-Belgium
Collaborators: Centre of Excellence for Vectors and Vector-Borne Diseases, Faculty of Science, Mahidol University, Thailand; Department of Society and Health, Faculty of Social Science and Humanities, Mahidol University, Thailand; Department of Veterinary Public Health, Faculty of Veterinary Medicine, Kasetsart University, Thailand; Department of Disease Control, Thai Ministry of Public Health; Department of Medical Science, Thai Ministry of Public Health
