Imagine the day when we can lure and trap mosquitoes with baits that are more attractive to the female mosquito than any human being? Imagine if we could drastically improve the control of malaria – which affects 10% of the South African population each year – and even eliminate it in the country?

This dream of the University of Pretoria Institute for Sustainable Malaria Control (UP ISMC) has also motivated analytical chemists to develop something more attractive than humans upon which mosquitoes can feed. For more than a decade, UP ISMC’s analytical chemistry team has been researching human skin emanations with the goal of recreating chemical mixtures that mimic the scent of the most mosquito-attractive human being.

Professor Egmont Rohwer, who initiated the project and works with team members Dr Yvette Naudé and Dr Madelien Wooding of the Department of Chemistry in the Faculty of Natural and Agricultural Sciences, elaborates: “A novel silicone rubber skin-sampler, worn as a patch on the forearm for 30 minutes, was successfully developed to capture thousands of compounds accurately for later release and analysis by sophisticated, state-of-the-art separation and identification techniques.” 

This provides reliable skin-emission profiles that can be processed by computerised pattern recognition techniques, allowing for chemical fingerprinting of metabolites originating from the infective agent and clues for designing a better lure for mosquitoes.

“The best available mixtures thus far use up to 12 different compounds,” Prof Rohwer says. “We believe we require a lot more and that their relative concentrations – an aspect that has not received a lot of attention – would be crucial to provide the irresistible lure. This is a massive challenge and test for our team’s international reputation in the research fields of chromatography and mass spectrometry. Our scientists have successfully diagnosed tuberculosis by this means and have obtained promising results for the screening of malaria.”

Early results indicate that identifying latent cases might also be possible, which is important for malaria elimination as trans-border movement of asymptomatic carriers could be a significant reservoir of the Plasmodium parasite. Latent cases are carriers of malaria that show no symptoms but carry the parasite in the liver, spleen or bone marrow. Such cases are generally not found with the existing blood microscope test, the rapid diagnostic test, and the more sensitive and selective DNA-based tests.

Adding to the arsenal

The most successful tools available to keep malaria at bay are insecticide-treated bed nets (ITNs) and indoor residual spraying (IRS). The latter refers to the annual spraying of long-lasting insecticides on indoor walls to target female mosquitoes that often rest here before biting humans for their blood meal. This is where transmission occurs. Consistent implementation of IRS requires enormous manpower and funding.

Another challenge to eliminating malaria in South Africa is the influx of citizens who come from neighbouring countries where there is a higher malaria risk and who may be asymptomatic carriers of the Plasmodium parasites. A cheap and successful chemical lure-based trap, together with efficient screening of trans-border visitors for malaria, would go a long way to eliminate the disease in South Africa.

The UP ISMC team considers their “magic scent mixture” to be a missing third partner of IRS and ITNs as they work towards ending malaria.

“Another heart-warming result of our published skin-analysis research is an invitation by a top US-based research group to participate in a unique programme in Zambia where mosquito-biting preference is studied in response to volatile scent profiles of a large group of people,” Prof Rohwer says. “The next challenge will be to extend our skin metabolic profiles technique to other species of mosquito (besides Anopheles arabiensis) and infective agents (beyond Plasmodium falciparum) to tackle other diseases spread by mosquitoes, such as Zika, chikungunya, West Nile and dengue fever.”

This story was originally featured in the Re.Search magazine. Check out Issue 10 of the magazine, which details some of our work, from advancing the field of wound care to understanding supermassive black holes.