Mosquitoes contribute to the transmission of potentially fatal diseases, including Zika virus, dengue, chikungunya, Rift Valley fever and malaria. Of these, malaria carries the greatest risk accounting for 229 million cases and over 400,000 deaths in 2019. Africa accounted for 67% (274,000) of all malaria deaths worldwide.
Malaria is caused by parasites that are transmitted to humans through the bites of infected female Anopheles mosquitoes. Vector control strategies such as indoor residual spraying and long-lasting insecticidal bed net programs have played a crucial role in reducing malaria cases.
But these interventions pose a number of problems.
First, the insecticide resistance of the main vectors of malaria in Africa is widespread and increasing.
Second, and related to this, is the fact that spraying and mosquito nets – alone or in combination – will not eradicate the incidences of malaria in high transmission areas. In particular, they are not effective in controlling Anopheles vectors. These feed and rest indoors and prefer to feed at night.
New strategies are therefore needed to complement current control strategies. The key to designing them is to understand what attracts and repels mosquitoes in certain people. This opens the door to new tools or strategies for the control and surveillance of malaria vectors such as chemical decoys and traps.
Our University of Pretoria research group is working on a project that seeks to answer the question: why do mosquitoes prefer some individuals to others?
We investigation whether there was a chemical difference in skin surface area between individuals who perceived themselves to be attractive to mosquitoes and those who were not. We were able to detect chemical differences between the two groups.
Our results open up two possible avenues of inquiry. First, chemical compounds closely associated with mosquito-attracting individuals could potentially be used in chemical decoys to trap mosquitoes outdoors. And second, compounds closely related to the fact that individuals are not attractive to mosquitoes could be developed into new repellents.
How mosquitoes find a meal
Female mosquitoes need a blood meal for their eggs to develop. First of all, the female mosquito must find its host. It can be quite selective. For example the Culex quinquefasciatus mosquito feeds exclusively on birds.
Mosquitoes are found in complex environments filled with many different signals or stimuli. Locating their preferred host involves a series of behavioral steps. It starts with the mosquito becoming aware of the host. This is usually done using long range signals such as carbon dioxide or visual signals.
The female mosquito then uses heat and humidity signals near the host, and finally the skin scent signals influence the selection of the landing and bite site. These skin surface chemical signals used for communications within a species are called semiochemicals.
The reason why mosquitoes prefer some individuals to others is probably due to the different semiochemicals found on the surface of human skin. But the complexity of the human skin surface is a challenge for chemical analysis. More than 500 skin compounds have been identified in studies conducted to date on human skin secretions. Many other chemicals remain unknown.
Sophisticated analytical techniques are now helping to find the identity of mosquito semiochemicals and potential semiochemical mixtures. Certain chemicals can work together to attract or repel mosquitoes.
The volunteers were compared based on their attractiveness to mosquitoes and whether mosquitoes preferred to bite certain areas of their skin.
Volatile and semi-volatile compounds – the compounds mosquitoes use to find and navigate to their human host – from a wide range of chemical classes – 69 in total – have been detected and identified as contributing to differences in their chemical profiles. skin surface.
To our knowledge, 31 of the compounds detected have not been previously reported on the surface of human skin.
We also define about to investigate the last step of the mosquito host search activity – landing on a suitable host followed by bites – using ultra-performance liquid chromatography with high resolution ion mobility mass spectrometry.
This allowed us to identify 20 compounds involved in ultimately biting mosquitoes.
The compounds we have identified could be useful in future malaria vector control programs, acting as attractants or repellents. Other biological studies will have to be carried out to test them on female mosquitoes.
The non-invasive skin sampling technique used by the research group laid the groundwork for mass screening of the surface of human skin, not only for vector control applications, but also for application in screening for human health.
This article is republished from The conversation under a Creative Commons license.