Dr Taneshka Kruger
Many people are already in holiday mode, spending their days and early evenings outside, often sitting with friends around a braai. They also tend to leave the windows open at night to allow the cool air in while they sleep. Unfortunately, the lovely summer weather brings with it a tiny and irritating nuisance that can spoil your mood, prevent you from falling asleep and leave you with annoying itchy, red bumps.
Mosquitoes are more than just irritating insects. They transmit various life-threatening diseases such as malaria, the Zika virus, yellow fever, dengue fever, Rift Valley fever and chikungunya. These mosquito-borne diseases account for more than 750 000 deaths annually, of which about two thirds are due to malaria. Approximately 3.2 billion people globally are at risk of getting malaria; fortunately, the disease is both preventable and treatable.
The best way to prevent getting malaria and other mosquito-borne diseases is to avoid being bitten by the mosquito vectors. Only female mosquitoes take blood meals, as they need the iron and protein for egg development. They can suck about three milligrams of blood at a time through a straw-like mouth part, called a proboscis, which is specifically constructed to pierce the skin. During the feeding process, saliva lubricates the opening, and it is the saliva and the injury that cause the skin irritation. Female mosquitoes also feed on plant sap and nectar, as males do.
Mosquitoes locate their hosts through carbon dioxide (CO2) detection. During metabolic processes, human and animal hosts produce CO2 as an end product.
Anthropophilic mosquitoes – those that prefer human blood – are attracted by human skin odours. The attraction is largely dependent on skin-odour profiles. The odour is caused by microbes, the skin-microbiome or skin flora, that live on your skin. Researchers at the University of Pretoria Institute for Sustainable Malaria Control (UP ISMC) are studying the skin microbiome’s effect on mosquito attraction and repellence, which is key to developing safer alternative malaria vector control techniques.
Genetics determine several other factors that can influence mosquito attraction; people with blood type O, for example, appear to attract mosquitoes more regularly. Mosquitoes also make use of secondary cues to locate their target.
Avoidance is better than cure
By understanding what makes these insects tick, you can avoid being bitten. Mosquito activity is mainly species-dependent; some (Aedes) are more active during the day, while others are more active at night. Malaria-transmitting Anopheles mosquitoes, and most other species, are usually active between dusk and dawn. It is best to avoid being outside during peak biting hours, but if you do need to go out during that time, wear long-sleeved clothes and shoes with socks. Avoid wearing dark colours, as this attracts Page 2 of 3 mosquitoes. When flying, these insects tend to stay close to the ground to avoid even the slightest breeze. They “see” their targets as silhouettes, and darker colours stand out more. You cannot cover your entire body, especially in warm weather, but you can apply insect repellent to exposed skin. Follow the instructions for safe application and reapply often. Anti-mosquito sprays or insecticide dispensers are useful, and it is a good idea to burn mosquito coils at night.
Biting can also be limited by using a fan, both indoors and outdoors. The air movement caused by the fan will make it difficult for the mosquito to fly and reach her target. Use screens over windows and doorways to keep mosquitoes from entering your home. When sleeping, especially in malaria-endemic areas, try to sleep under a bed net treated with an insecticide.
Malaria and COVID-19
With the borders open and travel no longer limited, more people will be travelling to malaria-endemic areas, such as the Kruger National Park and Mozambique, for the holiday season. Travellers need to protect themselves from being bitten by malaria vectors. Bear in mind that COVID-19 and malaria have similar symptoms: both diseases start with a mild fever, which can rapidly become more severe. It is imperative that anyone with malaria-like symptoms receive immediate treatment.
Dr Taneshka Kruger is project manager at the University of Pretoria Institute for Sustainable Malaria Control.