Vector control in South-East Asia
Programme overview
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, South-East 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.
However, South-East 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.
The projects
Climate change is predicted to have a profound effect on the intensity and distribution of certain vector-borne diseases in Africa. The programme examined what was likely to happen where, and how to help communities adapt to changing climatic conditions.
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 used 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, greater. […] 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 South-East Asia: Using the super-sterile mosquito technique to prevent mosquito-transmitted diseases
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 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.
Background
What is the situation of dengue 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, but 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, the whole society.”
— Dr Chea Thy, Co-Investigator, SESR-based strategies in Cambodia; and, Manager, Dengue Vector Control Programme, Phnom Penh, Cambodia
What is the situation of dengue in Thailand
"This year 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 support 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.
Financial and technical support
This project is undertaken through financial and technical support from the Special Programme for Research and Training in Tropical Diseases, World Health Organization, Geneva, Switzerland.
Vector birth control in Southeast Asia
The partners involved in the study on vector birth control in Southeast Asia are:
- Center 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, Ministry of Public Health, Thailand
- Department of Medical Science, Ministry of Public Health, Thailand
- Thailand Institute of Nuclear Technology, Ministry of Science and Technology, Thailand
- Go Green Company Limited, Thailand (Mahidol University Spin-Off Company for Green Products)
Dengue vector control in Cambodia
The partners involved in the study on Dengue vector control in Cambodia are:
- Malaria Consortium
- Centre National Malariology/Ministry of Public Health
- Ministry of Education (Cambodia)
- Bournemouth University UK
- Global Health Asia Institute (Mahidol University)
- Institute of Tropical Medicine (Belgium)
How do partnerships play an important role?
“we can’t assume as researchers that we know what the best intervention is because the best intervention relies deeply on the local context and without that partnership we’re not going to be able to be effective in making sure we cut down the number of people who suffer from dengue.” – Dr Kristie Ebi, School of Public Health, University of Washington
Why is an interdisciplinary approach so important
“[An interdisciplinary approach is] the recognition that the problems we face on the globe today, not only health, but broadly health, environment and others as well, are way too complex for any one discipline to find answers.” – Prof. Nancy Lewis, East-West Center, University of Hawaii; Chair, WHO/TDR Special Project Team