Arboviruses or arthropod-borne viruses, such as dengue, Zika and chikungunya represent a huge burden for tropical and sub-tropical human populations. It has been estimated that, every year, 390 million new cases of arboviruses occur in 128 countries and 3.9 billion people are at risk.

Vector control strategies are based on mechanical destruction of mosquito breeding sites and application of insecticides, which, due to continuous and massive usage of different chemicals, have been contributing to the development of insect resistance in many countries. Based on this complex scenario, novel and sustainable strategies are urgently needed, which can be used in an integrated control program by the governments of affected countries. Biological control strategies, involving mosquito pathogenic or pathogen-interfering organisms such as fungus or bacteria are possible, environmentally friendly, candidates.

Wolbachia is an intracellular bacterium present in more than 60% of all insect species, worldwide. It manipulates the reproduction of insects, in order to be successfully maintained in the system, through a mechanism called cytoplasmic incompatibility, or CI. When Wolbachia-infected males mate with uninfected females, no progeny is produced. On the other hand, females can mate with either infected or uninfected males and will produce eggs, most frequently, 100% Wolbachia-infected, the so-called, vertical transmission (Fig. 1). This mechanism, among others caused by Wolbachia, promotes reproduction advantage towards infected insects. Although present in several mosquito species, the bacterium was never found in Aedes aegypti, the main vector for dengue, Zika, and chikungunya, worldwide. In the laboratory, back in 2005 in Australia, WMP researchers were able to introduce a specific strain of this bacterium, into Aedes aegypti embryos, after having isolated it from the fruit fly, Drosophila melanogaster. After this successful transinfection, it has been discovered that, when the bacterium is present in the mosquito, viruses do not replicate well, therefore reducing their transmission ability. This strategy does not involve any kind of genetic modification.

An example of translational research

The World Mosquito Program (WMP) is a not-for-profit initiative, working to protect the human population from mosquito-borne diseases. WMP proposes an innovative method of releasing Aedes aegypti mosquitoes into the environment with the Wolbachia microorganism, which reduces the ability of the mosquito to transmit dengue, Zika, and chikungunya. The Wolbachia method is safe, natural, and self-sustaining, and has the potential to achieve significant public health impact in areas endemic to these viruses.

WMP was formerly known as “Eliminate Dengue: Our Challenge.” The name has been changed due to rapid global program expansion and also to reflect that the method works against several diseases, not just dengue. WMP is active in 12 countries: Australia, Vietnam, Indonesia, Pacific Islands (Fiji, Vanuatu, Kiribati, New Caledonia), India, Sri Lanka, Colombia, Mexico, and Brazil, and discussions are at an advanced stage with several others. In Brazil, it has been conducted since 2012 by the Fundação Oswaldo Cruz (Fiocruz), based in Rio de Janeiro.

The aim of WMP is to perform controlled releases of Aedes aegypti containing Wolbachia, so there will be a gradient substitution of local the Aedes aegypti population by Aedes aegypti with Wolbachia. This is possible, through both the CI mechanism and the vertical transmission, guaranteeing the self-sustainability of the method.

Steps of Wolbachia Method

To achieve the goal of substitution of the local population of Aedes aegypti with Aedes aegypti with Wolbachia, the actions of WMP are divided into three main stages. (i) In the Community Engagement phase, project teams interact with the population and institutions (health clinics, schools, community leaders) for disseminating information about the initiative. At this stage, surveys are conducted to measure understanding and acceptance of the local population about the method. In addition, a Community Reference Group is set up, a local committee who monitors all actions taken in the locality, and communication channels are established with the community, including telephone, e-mail, face-to-face interactions, and social media. (ii) After the Community Engagement phase and community approval begins the release of Aedes aegypti mosquitoes with Wolbachia. Mosquitoes are bred in the Fiocruz insectary, which has similar humidity and temperature characteristics as those that mosquitoes encounter in the external environment. Adult releases happen in the early hours of the morning and are made by car. In some regions, this work is done on foot, by health surveillance agents and community health agents of the municipal governments of Rio de Janeiro and Niterói. (iii) Monitoring of the Aedes aegypti population in these areas initiate during mosquito releases. Traps are installed in homes or commercial establishments that voluntarily provide a location for the traps. Weekly, technicians go to these sites to collect mosquitoes. At the project facilities, the captured mosquitoes are separated, identified and the Aedes aegypti are sent to the Diagnostic Laboratory, where they are checked individually. This analysis aims to identify the DNA of Wolbachia bacteria in the mosquito organism and is an indicator of the establishment of the local mosquito population with Wolbachia.

Large-scale expansion

WMP began preparative studies in Brazil in 2012 and ethical and regulatory approvals. In 2014, releases began in the pilot areas, Jurujuba, in Niterói-RJ, and Tubiacanga, in the city of Rio de Janeiro. The last releases of mosquitoes at these sites were carried out in January 2016, and since then monitoring has revealed Wolbachia's establishment of more than 90%. In November 2016, large-scale expansion began for 28 neighborhoods in Niterói, to protect 270,000 people.

In Rio de Janeiro, large-scale releases began in August 2017, with the plan of reaching 19 neighborhoods, where 0.9 million people live. Concomitantly with community engagement, mosquito release and monitoring activities, an epidemiological study is underway to measure the impact of our work in reducing disease transmission. Preliminary results show already a reduction on the incidence of dengue, Zika, and chikungunya in areas where Wolbachia is present.

Through a partnership with the city of Belo Horizonte, WMP Brazil will start activities in an pilot area with 60,000 inhabitants, probably in late 2019.

Regulatory and ethical approvals

For pilot projects, regulatory and ethical approvals were granted in 2014. The Temporary Special Registry (Registro Especial Temporário–RET–, in Portuguese) was granted after evaluating the project simultaneously by three governmental areas: National Agency of Sanitary Surveillance–ANVISA–, Ministry of Agriculture, Livestock and Supply–MAPA–, and the Brazilian Institute of Environment and Renewable Natural Resources–IBAMA. Ethical approval was also granted in early 2014, following a thorough evaluation by the National Commission for Research Ethics (CONEP). For the large-scale expansion, all the regulatory documents have been renewed.

In February 2016, the Ministry of Health recommended the Wolbachia method as promising in vector control in response to Zika's national emergency. This recommendation was reinforced in March of that year by the World Health Organization (WHO) through its Vector Control Advisory Group (VCAG).