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Bacteria and mosquitoes: understanding the newest scientific and regulatory advances

March 01, 2019

On 29 October 2018, the European Commission adopted the decision that bacteria (and preparations) of the genus Wolbachia used for creating non-naturally infected mosquitoes for vector control purposes are to be considered a biocidal product. Furthermore, non-naturally infected mosquitoes, irrespective of the infection technique used, are considered neither a biocidal product nor a treated article. 

In this article, Eneree Gundalai from TSG Consulting's biocides team explains what Wolbachia are, as well as the implications of the EC decision.

What are Wolbachia?

Wolbachia are intracellular bacteria that have evolved in some cases to be mutualistic rather than parasitic. Although they are naturally present in around 40 % of arthropods, there is a lack of evidence for natural Wolbachia infections in Aedes aegypti, the primary species responsible for transmitting human diseases such as Zika, dengue and chikungunya and the primary species of interest for vector control with this new biocide. Non-natural infections have to be carried out under laboratory conditions in order to create non-naturally infected mosquitoes with a suitable strain of the bacteria.
 
Vector control is achieved in two ways:
  1. Sterile insect technique - The cytoplasm of infected male sperm and non-infected female eggs are incompatible, resulting in the death of the eggs fertilized by this mating. Introducing a large number of infected males into the wild population will effectively sterilize a number of females, reducing the future population.
  2. Reduction of disease transmission - When Wolbachia is artificially forced to form a symbiosis with Aedes aegypti as a new mosquito host, it boosts the basal immune response and enhances the mosquitoes’ resistance to diseases.
When infected males and infected females are introduced into the wild population, they are able to spread rapidly because of cytoplasmic incompatibility, where all the infected females are able to produce viable and infected offspring with any male, so outcompeting the non-infected females who are rendered sterile should mating with infected males occur. Over time, more and more of the population will carry the symbiotic Wolbachia. This population replacement technique does not significantly reduce the number of mosquitoes, but it does interrupt disease transmission.

Minimizing Wolbachia biocide application

The maternal transmission of Wolbachia, in the laboratory and in the wild, is self-sustaining. Once critical mass for the infected population is established, it is no longer necessary to inoculate the Wolbachia into the mosquitoes. In light of the decision by the European Commission to consider the non-naturally infected mosquitoes as neither a biocidal product nor a treated article, the transportation of Wolbachia host populations is a viable method by which to minimize the use of Wolbachia as a biocidal product. The hosts, whether they be eggs, larvae or adults can be transported to laboratories to seed new populations.

Have a question?

If you have any questions about the EC decision on Wolbachia, please get in touch.