Vector control: multiple strategies to combat vectors
Vector-borne diseases such as malaria, dengue and Zika are responsible for more than a million deaths worldwide each year. They are transmitted by arthropod vectors. There is usually no vaccine nor any specific treatment against these diseases, and the main solution is therefore to control the insects that carry them. As part of its work to examine marketing authorisation applications, ANSES assesses the efficacy of biocides (insecticides and acaricides) and the risks associated with their use. It also funds research into other means of controlling insect vectors.
With climate change and globalisation, diseases caused by infectious agents carried by arthropods, especially mosquitoes, have been re-emerging in the past few years. The main ones are malaria, dengue, chikungunya and Zika. The tiger mosquito, a vector of several viruses, arrived in metropolitan France in 2004, and imported or autochthonous cases of dengue, chikungunya and Zika are now regularly detected. In this context and in the absence of specific vaccines and treatments, the main action taken is to control the mosquitoes transmitting the viruses responsible for these diseases. This control requires different strategies combining chemical and non-chemical methods.
Insecticides, a solution with limitations
Repeated use of the same insecticidal substance gives a selective advantage to resistant mosquitoes that then proliferate. Various active substances that were previously in use have been found to be hazardous to humans or the environment and have been gradually withdrawn from the market. There are currently very few active substances used for vector control in France. Treatments are primarily organised around one active substance targeting mosquito larvae, Bti, and another targeting adult mosquitoes, deltamethrin. However, the widespread use of deltamethrin, without alternating between other active substances, has led to the emergence of resistance among mosquitoes in the French overseas départements. Other substances and means of control therefore need to be developed.
ANSES's work on the identification of new substances against vectors
The use in France of biocidal products, including insecticides, is governed by European regulations. ANSES is responsible for assessing biocidal products in accordance with these regulations and issuing marketing authorisations. In order to identify potential alternatives that would improve the diversity of products that can be used in vector control, ANSES has over the past few years been compiling an inventory of active substances with reported or assumed activity on mosquitoes and their family, as well as other biting insects (flies, horseflies). A total of 129 substances have so far been identified. The Agency compared these compounds according to criteria of toxicity, ecotoxicity and environmental contamination. In 2012, this analysis led to the selection of 32 active substances (PDF) that could potentially be used against adult mosquitoes or larvae, on which the Agency recommended focusing research and development efforts. In 2016, this inventory was updated in light of the European regulatory framework and the possible medium-term use of these substances in France.
The Agency has also produced several opinions and reports on the use of impregnated mosquito nets during the 2006 chikungunya and 2016 Zika outbreaks.
Begin with the use of non-chemical methods
To avoid the emergence of resistance and limit the impact of products on humans and the environment, non-chemical methods should be favoured as far as possible. Treatments containing adulticide insecticides should be limited to occasional use intended to prevent the spread of the disease around contamination outbreaks, in a well-defined framework according to the epidemiological context and local conditions. ANSES recommends that their use should form part of an integrated control strategy, combining several approaches, including:
- community mobilisation and education of the public, to raise awareness about best practices for controlling mosquitoes and vector-borne diseases. The aim is to induce a lasting change in behaviour, in order to maintain measures to prevent mosquito bites, such as mechanical control;
- mechanical control: this can target larvae, by eliminating stagnant water in which mosquitoes lay their eggs, in flower pots, containers or old tyres, for example. Mechanical control can also target adult mosquitoes, with the use of traps;
- prevention of mosquito bites: this essentially involves individual protection. In the first instance, therefore, people are recommended to wear loose-fitting clothes that cover the body and to sleep under mosquito nets. If these non-chemical measures are insufficient, they should apply suitable repellents to the skin or clothing, opting for products with marketing authorisation and following the instructions for use, and use insecticide-impregnated mosquito nets.
Other innovative methods are also being examined, and ANSES has funded studies on alternatives to insecticides. In particular, the use of bacteria or viruses that kill mosquitoes is being considered. There have also been trial releases of male mosquitoes that cannot produce offspring, either because they have been made sterile or because they carry bacteria that make them incompatible with females.