World Mosquito Day
August 20th is World Mosquito Day, which marks the discovery in 1897 by British doctor Sir Ronald Ross that the female Anopheles mosquito transmits Malaria. This provided the foundation for scientists across the world to better understand the deadly role of mosquitoes in transmitting diseases.
Over recent decades many mosquito-borne diseases have emerged - or resurfaced - and spread rapidly, such as Zika, Dengue fever, West Nile fever and Chikungunya. Even Malaria, which has been the focus of many long-term global eradication efforts, has recently shown signs of increasing.
Many of these diseases have no specific treatment and the limited treatments that are available are facing the issue of drug resistance. Resistance to insecticides commonly used to control mosquitoes is increasing. Further innovation is 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 mosquito-borne diseases.
Here are a few examples of recent scientific developments that herald a new dawn in the fight against this global threat.
Fighting insecticide resistance with next-generation insecticides
In recent decades the 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 mosquito control. Without new products, vector control is doomed to failure, according to IVCC.
The WHO approved two new-generation insecticides in 2017. These are being distributed in malaria areas for use in IRS programmes by the NgenIRS project. Since 2016 the project has supported operations in 12 African countries and has bought over 4.5 million bottles of the new insecticides.
New odours to attract and repel mosquitoes
Mosquitoes find their human hosts by sensing the carbon dioxide we breathe out. However, 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 have 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 already in common use - which means that they don't need lengthy and costly safety testing - to study further:
- Ethyl pyruvate, 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. They are doing this by capturing and analysing the DNA 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, the Commonwealth Scientific and Industrial Research Organisation (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 of males, infecting them with Wolbachia bacteria and then releasing large numbers of the infected 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 reduced local Aedes mosquito populations 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 the transmission to humans. Many research projects in multiple disciplines are therefore 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 during a Dengue virus infection of the cells lining the gut. The virus requires several biochemical pathways in the mosquito in order to replicate. Therefore finding ways to block them is now the target of further research.
Knocking out mosquito genes
Using a tool called CRISPR/Cas9, another team of researchers at Johns Hopkins University has developed a new gene-editing procedure for Anopheles mosquitoes. 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 before they can be released into the wild and their impact on reducing mosquito-borne diseases 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 as scientific developments across many disciplines are combining to find 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.
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