Do mosquitoes prefer to bite certain humans over others? Seems to be true when different people in a group at an outdoor gathering respond differently to the buzzing menace. While some report itches and rash-like bumps, others remain unscathed. This has prompted research on what attracts certain mosquitoes to certain humans in the first place. Most importantly, are mosquitoes then selective?
Dr Laxman Jessani, Consultant, Infectious Disease Specialist, Apollo Hospitals, Navi Mumbai, says several studies have found different triggers. “Generally speaking, mosquitoes appear to be more attracted to people with blood type O than other blood types, A being the least.” The US-based NIH study has also shown that those with blood group O, though bitten often, are far less likely to get severe malaria than those with other blood groups if they are bitten by the malaria bug carrying Anopheles.
“The available research indicates so but many other additional factors could also play a role in a person’s attractiveness to mosquitoes. The greater the number of bacteria on the feet, the more attractive they are to the mosquitoes. Individuals with a higher microbial diversity are less attractive to mosquitoes and may, therefore, get fewer bites,” says Dr Jessani.
The microbes sitting on our skin affect the chemicals we release. Skin bacteria convert compounds in our sweat and sebum into volatile compounds. Now some of these could either attract or repel mosquitoes. A study in May this year and published in Nature suggests that two saturated fatty aldehydes — decanal and undecanal — are odorants that attract mosquitos. Sebum composition and long-chain aldehyde levels vary between people, suggesting that mosquitoes would also get attracted differently.
Various studies seem to suggest other factors. For example, a study by Royal Society Open Science suggests that three different disease-carrying mosquito species are activated and attracted by carbon dioxide (CO2). Humans and most animals give off carbon dioxide, heat and moisture as a result of cellular respiration. A 2015 study edited by the New Mexico State University has found that “female mosquitoes display preferences for certain individuals over others, which is determined by differences in volatile chemicals produced by the human body and detected by mosquitoes. Body odour can be controlled genetically but the existence of a genetic basis for differential attraction to insects has never been formally demonstrated. This study investigated heritability of attractiveness to mosquitoes by evaluating the response of Aedes aegypti (Stegomyia aegypti) mosquitoes to odours from the hands of identical and non-identical twins in a dual-choice assay. Volatiles from individuals in an identical twin pair showed a high correlation in attractiveness to mosquitoes, while non-identical twin pairs showed a significantly lower correlation.” Yet other studies link mosquitoes following you to lactic acid secretion.
“In the end, whatever be the reason, make sure you keep mosquitoes away now that dengue season is upon us with the rains. Use mosquito repellents and lotions on your skin. Also, get a regular fumigation done by municipal authorities to prevent breeding of mosquitoes, thereby reducing their bites. Make sure there’s no stagnant water in garden pots where mosquitoes can breed,” advises Dr Jessani.