Mosquitoes: Carriers of diseases, humans’ biggest enemies. Prevalent arguments about the attractiveness of mosquitoes cleavage into: The amount of Carbon Dioxide a person exhales or the different blood types of humans. A recent study on the globally invasive mosquito Aedes aegypti reveals the relationship between human body skin-derived chemicals and mosquito attraction. More specifically, the carboxylic acid level. This passage will demonstrate the research's results, conclusion, and limitations.
It is shown that mosquitoes use two large multigene families to detect olfactory signals that encode odor-gated ion channels: the odorant receptors (ORs) and the ionotropic receptors (IRs). Odorant-gated ion channels consist of four subunits symmetrically arranged around a central pore. A small anchor domain connects the subunits; the channel’s outer regions detect chemicals in the environment. There are hundreds of ligand-selective ORs and IRs in a random insect species, but only one OR co-receptor (Orco) and three IR co-receptors (Ir8a, Ir76b, and Ir25a.) in every insect. In tandem, these odor-gated ion channels sense chemical ligands. ORs are typically responsive to ketones, esters, and IRs to carboxylic acids and amines. In the study, OR is not focused. Mutating the IR pathway produces more intense effects on mosquito attraction to humans.
The experiment tests the attractiveness of Aedes aegypti for different humans, therefore discriminating the chemicals from the high-attractive individuals and the low-attractive individuals. In this experiment, nylons worn by the experimental subjects are conserved for long-term tests. A constant amount of CO2 is added to all experiments, stimulating the mosquitoes and mimicking real-world situations. Unlike previous odor experiments, scientists in this experiment use the two-way behavioral assay as it provides an easier comparison between high-attractive individuals and low-attractive individuals.
The research tested the mosquitoes lacking Orco retained strong attraction to humans, but show deficits in discriminating humans from non-human animals (DeGennaro et al., 2013). From the results shown below, the Orco mutants retain the ability to distinguish between highly attractive subjects and low attractive subjects. The Ir8a mutants also show similar abilities. This concludes that olfactory disability still can let mosquitoes retain the ability to distinguish between attractive individuals.
Concluded from the graph above, Ir25a mutants and Ir76b mutants both show a significant decrease in attraction for humans but retained the ability to distinguish highly attractive individuals and less attractive individuals. These facts suggest that mosquitoes have evolved particularly redundant sensory structures letting them hold appeal to human beings regardless of the enormous genetic disruption of their olfactory gadget. Further concluded from the data, mutating in the IR pathways post a greater effect on the attractiveness than mutation in the OR pathways. This provided a conclusion that non-mutant mosquitoes’ attractiveness to humans relies heavily on the acid level. Performing a GC/QTOF-MS analysis focused on the acidic compounds found in the nylons worn by the experimental subjects, scientists were able to identify 204 molecular capabilities that have been enriched on subject nylons as opposed to unworn nylons and technique blanks.
Using metabolomic experiments, scientists were able to identify 13 chemical compounds enriched in high attractor groups. Three of those compounds were identified as pentadecanoic acid, heptadecanoic acid, and nonadecanoic acid. Further experiments introducing a new cohort of humans were conducted and the result was re-analyzed a year later, presenting an astonishing result that human skin-derived compounds are consistent even after a significant one-year span. However, a clear cleavage indicating the direct relationship between human skin carboxylic acid level and mosquito attraction is not shown. It remains unclear if the rise in carboxylic acid levels has a unidirectional relationship with mosquito attraction, and it is unknown whether the rise in carboxylic acid levels is a cause for a spike of other mosquito attractive factors. Although an authentic answer is still hidden, a reduction in specific carboxylic acids does decrease the mosquitoes’ affection for humans.
Humans have extra plentiful loose fatty acids on their skin surface than non-human animals. From the vast data, it is thought that different individuals will unlikely produce the identical complement of acids with the same ratio, providing different chemical signatures for different humans. The reason behind this is human skin microbiota. Skin bacteria contribute to the pool of free fatty acids found on human skin by producing several types of fatty acid synthetase enzymes that allow them to produce diverse types of acids themselves (Kaneda, 1991; Lu et al., 2004). It is to say this factor alters the human skin-derived acids, which to some extent contribute to the attraction of mosquitoes. Additionally, the human skin microbiota’s composition is remarkably stable with time, although skin is exposed to a constantly fluctuating environment (Oh et al., 2016). Therefore, changing the skin microbiota of a person could prevent him/her from being a “mosquito magnet”.
The prospects of this finding are significant. First, by successfully knowing the biting mechanism of mosquitoes, mosquito-associated diseases, such as malaria, can be controlled using this factor. Targeting prevention can be used to deal with the invasive Aedes aegypti, reducing the spread of arbovirus. For example, disrupting the microbiota on the human skin, reducing the amount of carboxylic produced, and conclusively lessening the attraction of highly attractive individuals. Natural chemical repellants are also found, countering the effect of a high carboxylic acid level. Chemical compounds five—6-methyl-5-hepten-2-one, octanal, nonanal, decanal, and geranylacetone are found in low-attractive humans. This is used to explain the anomalous result. Knowing those distinct compounds, repellants could be made to oust Aedes aegypti.