01. What is the current dengue situation in Vietnam?
Dengue fever is endemic in Vietnam, with around 150,000 cases reported each year. From these 50 to 100 people die, the majority being children. Over the past 10 years the number of dengue cases has significantly increased, which authorities attribute to changes in household water supply infrastructure, urbanisation and an increasingly mobile population.
Current control methods focus on community education campaigns and response to dengue outbreaks through insecticide spraying in affected areas.
02. How long has Eliminate Dengue been working in Vietnam and who is involved in the research?
The Eliminate Dengue program began laboratory research at the National Institute of Hygiene and Epidemiology (NIHE) in Hanoi in 2006. The Institute Pasteur Nha Trang joined the program in 2007 when the potential field site of Tri Nguyen Island, 2km from the port of Nha Trang in Khanh Hoa province, was chosen as the preferred first field trial site in Vietnam. From 2012, the Khanh Hoa Health Department also became involved as a project partner, supervising implementation and monitoring of project activities on Tri Nguyen Island.
The project is overseen by the Ministry of Health and receives technical support from international institutions including Oxford University Clinical Research Unit and Monash University.
03. What activities has the Eliminate Dengue project undertaken in Vietnam?
With community support and government approval, a field trial took place on Tri Nguyen Island from May to November 2014 involving the release of mosquitoes that carry the wMel strain of Wolbachia. This followed an earlier trial on the island from April 2013 to September 2013, which involved the release of mosquitoes with the wMelPop strain of Wolbachia.
Prior to these field trials, initial activities in Vietnam focused on establishing laboratory populations of Wolbachia-carrying Aedes aegypti reared from wild mosquitoes taken from Tri Nguyen Island (Wolbachia is passed from mother to offspring through the eggs). We have carried out experiments on these mosquitoes to test for the effects of Wolbachia on the mosquitoes, as well as any adverse effects that these Wolbachia mosquitoes could cause to humans, animals and the environment. Our findings are consistent with those in Australia, showing that Wolbachia blocks the dengue virus and causes no detectable adverse effects.
The team has been monitoring the mosquito population in Nha Trang since 2015 and is now preparing for further field trials in Nha Trang city.
04. Who gave approval for the release in Vietnam?
The Ministry of Health in Vietnam gave approval for the release of Wolbachia mosquitoes on Tri Nguyen Island following consideration of the recommendations from the Ministry’s Ethical and Technical Review Board. The review board is made up of 20 members all currently conducting health research in Vietnam.
05. Why was Tri Nguyen Island chosen as the pilot release site in Vietnam?
Tri Nguyen Island, with a population of approximately 3250 people in 825 houses, was chosen because it has medium to high Aedes aegypti populations throughout the year, has easily accessible mosquito breeding sites (eg. household water storage containers), and is located in close vicinity of the Institute Pasteur Nha Trang. Importantly, it is also a geographically isolated site, allowing the program team to easily monitor the release of Wolbachia mosquitoes.
06. Did the residents of Tri Nguyen Island support the release of Wolbachia mosquitoes?
Over 95% of householders on the island showed their support for the trials by completing a registration form.
07. What does a field trial involve?
Before releasing mosquitoes, the project team reduces the number of wild mosquitoes on the island by using sweep nets to clear water containers of wild Aedes aegypti. With residents' permission, and approval from the Ministry of Health, we then release Wolbachia Aedes aegypti once a week for approximately three to four months. This can involve releasing adult Wolbachia mosquitoes or mosquito pupae. During and after the release period, we also monitor how many mosquitoes on the island carry Wolbachia.
08. What did you learn from the 2013 wMelPop trial?
Our goal for this field trial was to see if we could introduce and establish the strongest dengue blocking Wolbachia strain (wMelPop) into the wild Aedes aegypti population on Tri Nguyen Island.
While the wMelPop rate in the mosquito population initially reached a high level, results showed a decline in the number of mosquitoes carrying this strain. We now understand that this is because the wMelPop strain of Wolbachia causes mosquitoes to have a shorter lifespan and lay fewer eggs than the wild mosquitoes. This means wMelPop mosquitoes produce fewer offspring than other mosquitoes, making it difficult for this strain to establish in the local mosquito population.
From May to November 2014 we returned to the island for a second trial, releasing mosquitoes with the wMel strain of Wolbachia. Laboratory results from Vietnam’s National Institute of Hygiene and Epidemiology (NIHE) show that this strain of Wolbachia is suitable for the island’s environment.
09. What results have you seen from the 2014 wMel field trial on Tri Nguyen Island?
Our goal for this field trial was to introduce and establish the wMel strain of Wolbachia in the wild Aedes aegypti mosquito population on Tri Nguyen Island. In the months following the releases, we have seen ongoing high levels of Wolbachia in the local mosquito population. We hope to see Wolbachia remain at a high level and, if successful, we expect to see less risk of local dengue transmission on the island.
10. Has the project in Vietnam undertaken a risk assessment and if so, what were the main findings?
An extensive risk assessment was conducted in 2011. Over 30 experts from the fields of public health, entomology, ecology and socio econominc studies were involved in the assessment.
The assessment concluded: “It is estimated that there would be a negligible risk of the release of Aedes aegypti containing Wolbachia resulting in more harm than that currently caused by naturally occurring Aedes aegypti over a 30 year timeframe."
11. What are the next steps for Eliminate Dengue project in Vietnam?
In 2015, a new project office was established in Nha Trang, a city of more than 400,000 people. Initial activities have focused on monitoring the local mosquito population and collecting information about the existing levels of dengue.
In 2017, Eliminate Dengue Vietnam plans to initiate a field trial in 4 pilot wards of Nha Trang city. The aim of these trials is to establish Wolbachia across the 4 wards, which is expected to reduce local transmission of dengue and other mosquito-borne viruses.