Over recent decades many mosquito-borne diseases have resurfaced or emerged and spread rapidly. From Zika, dengue to West Nile fever and chikungunya. Even malaria, which has had long-term global efforts to eradicate it, has recently shown signs of increasing.
Many of these diseases have no specific treatment and the limited medicines available for some are facing resistance. Insecticides used to control mosquitoes are also facing resistance. On many fronts, innovations are urgently needed to control old diseases and prevent new ones from spreading.
Scientists in fields as diverse as biochemistry, genomics, entomology, computing, remote sensing, avionics, artificial intelligence, robotics and aerospace engineering are combining their resources to develop new ways to fight diseases.
Here are a some recent scientific developments that are bringing a new dawn in the global fight against mosquito-borne diseases.
Fighting insecticide resistance with next-generation insecticides
In recent decades Anopheles and Aedes mosquito populations in various parts of the world have built up resistance to many of the available insecticides and larvicides used for vector control. Without new products vector control is “doomed to failure”, according to IVCC.
Two new-generation insecticides were approved by WHO in 2017. These are being distributed in malaria areas for use in indoor residual spraying (IRS) programmes by the NgenIRS project. Since 2016 the project has supported operations in 12 African countries and bought over 4.5 million bottles of the new insecticides.
New odours to attract and repel mosquitoes
Mosquitoes find human hosts by sensing the carbon dioxide we breathe out. But when they get close they locate sites for feeding by detecting volatile chemicals given off by human skin. Researchers at the University of California Riverside used modern chemical screening techniques to test half a million compounds in a chemical database to find those that could trigger mosquito sensing organs.
They chose two compounds that are already in common use, so don’t need lengthy and costly safety testing, to study further:
- ethyl pyruvate, which is a food flavouring with a fruity flavour: this was found to reduce Aedes aegypti attraction
- cyclopentanone, a mint-smelling flavour and fragrance: this was a powerful attractant for Culex quinquefasciatus mosquitoes
Robotics, gene sequencing and cloud computing to detect diseases early
Project Premonition is developing a high-tech system to identify potential disease outbreaks before they happen. The system captures and analyses the DNA and RNA of mosquitoes that have fed on local animals that could be reservoirs of diseases. The project is a collaboration between Microsoft Research (MSR) and several US universities.
The project is developing:
- Autonomous drones that can locate mosquito hotspots in complex environments containing trees and buildings
- Robotic traps to collect and identify mosquito specimens
- Genomics, cloud computing and machine learning algorithms to analyse the DNA and RNA in the mosquito samples
The genomics part of the project can already identify the correct mixture of organisms — animals, mosquitoes and pathogens — with 99.9% accuracy.
Releasing mosquitoes infected with Wolbachia bacteria
In July this year, CSIRO announced the successful results of a project that released millions of sterile male Aedes aegypti mosquitoes on the Cassowary coast in Queensland, Australia. The project uses new techniques developed by Verily (owned by Alphabet, the parent company of Google) for large-scale rearing, sorting out the males, infecting them with Wolbachia bacteria — which are widespread in nature in many insects — and releasing large numbers of the mosquitoes. The Wolbachia prevents the females producing viable eggs.
Verily is also developing software, monitoring tools, sensors and traps to indicate the mosquito hotspots where the treatment is most effective. The early results show that local Aedes mosquito populations were reduced by 80% — a promising example of the potential of new scientific developments in fighting the global threat of mosquito-borne diseases.
A gut feeling to blocking diseases
The midgut of mosquitoes is the initial site of infection for a range of diseases, therefore finding a way to block infections there will also block transmission to humans. Many research projects in multiple disciplines are looking at novel ways to do this, including:
Preventing fungal infections
Researchers at Johns Hopkins University in the US found that a common fungus, Talaromyces, can infect Aedes aegypti mosquitoes and make them more susceptible to the dengue virus. The researchers also found that a Penicillium fungus made Anopheles mosquitoes more susceptible to infection with the malaria parasite. The research suggests that antifungal solutions are a potential alternative to insecticide spraying to protect the mosquitoes from diseases they might spread to humans.
Biochemical modification of the mosquito gut
Another study at Colorado State University has made the first comprehensive analysis of the complex biochemical interactions that occur in a mosquito when a dengue virus infects the cells lining its gut. Using high-resolution mass spectrometry the researchers identified several biochemical pathways in the mosquito that are required for the virus to replicate. These are now targets for further research to find ways to block them.
Knocking out mosquito genes
Another team of researchers at Johns Hopkins University developed a new gene-editing procedure for Anopheles mosquitoes using a tool called CRISPR/Cas9. Their procedure knocks out the Anopheles mosquito gene FREP1 that enables the Plasmodium parasite to infect the cells lining the midgut. The mutant mosquitoes showed a significant decrease in infection with the parasite. Further work is needed, however, before they can be released to breed with the wild population and their prospective impact in reducing the threat of malaria can be examined.
Medicines for Malaria Venture (MMV) has a partnership network of over 400 pharmaceutical, academic and endemic-country partners in 55 countries developing drugs to protect against malaria.
Since its foundation in 1999, the network has brought seven new medicines to market that are already being used to prevent and treat the disease. As recently as July this year the US FDA endorsed tafenoquine, another medicine produced under the programme. This targets the dormant liver stage of Plasmodium vivax and is the first new medicine for 60 years for this type of treatment.
The future for controlling mosquito-borne diseases is looking more promising than in recent years. The examples described above show that developments in many scientific disciplines are providing new ways of treating diseases and controlling mosquitoes.
As part of our commitment to fighting mosquito-borne diseases, Rentokil Initial is establishing a new global centre of excellence for mosquito control, the only commercial pest control company to have such a facility.
Listen to Andy Ransom, CEO of Rentokil Initial, discuss the size of the threat from mosquitoes and what Rentokil is doing to help in commemoration of World Mosquito Day on 20 August.