It is well documented that mosquitoes use chemical compounds present on the human skin surface to locate and ultimately bite their human host. But why do mosquitoes prefer certain individuals above others? 

This was the research question set out to be answered by Madelien Wooding, PhD candidate, under the supervision of Dr Yvette Naudé and the co-supervision of Prof Egmont Rohwer, from the Department of Chemistry. 

With the aid of sophisticated analytical equipment, the search to uncover the chemical compounds that make people attractive, or not, for mosquitoes was on. Using an in-house developed non-invasive polydimethylsiloxane (PDMS) sampler, worn as a bracelet or an ankle, enabled the research group to sample the skin surface of 20 individuals without causing any discomfort or unease. 

The human volunteers were compared based on perceived inter-human attractiveness for mosquitoes, and as well as inter- and intra-human mosquito biting site preference. Volatile and semi-volatile compounds (these are the compounds mosquitoes use to find and navigate towards their human host) from a broad range of chemical classes, 69 in total, were detected and identified as contributing to the differences in their surface skin chemical profiles, using comprehensive gas chromatography coupled to time-of-flight mass spectrometry (GC×GC-TOFMS). 

According to Ms Wooding, “the final step in the mosquito host-seeking activity, i.e. landing on a suitable host followed by biting, was investigated using ultra-performance liquid chromatography with ion mobility high-resolution mass spectrometry (UPLC-IMS-HRMS).This facilitated the further identification of 20 non-volatile and semi-volatile biomarkers (these are the compounds involved in the final host acceptance, i.e. biting, by mosquitoes), discerning a difference in perceived mosquito attractiveness.” 

The identified biomarkers are of great importance as lead compounds in future malaria vector control programmes, acting as attractants or repellents. The non-invasive skin sampling technique used by the research group has laid the foundation for the mass screening of the human skin surface metabolome, not only for vector control applications, but also for application to human health screenings. 

Skin volatile research and malaria

The University of Pretoria Institute for Sustainable Malaria Control (UP ISMC) - in an article on how to avoid mosquito bites - briefly touched on the role that skin volatiles play in host preferences for specialist feeding behaviour in mosquitoes. Understanding what attracts and repels mosquitoes can result in novel and innovative tools or strategies for malaria vector control and surveillance. Malaria vector surveillance is important for the evaluation of existing malaria control programmes and can facilitate appropriate and timely decisions regarding interventions. The UP ISMC is proud of the research done by this team and its potential contribution towards the malaria elimination agenda.  

This research was published in the Journal of Separation Science and in Analytical and Bioanalytical Chemistry.