These new insights might lead to a new line of clinical laboratory testing, particularly if the results could guide the patient to microbiome-based repellents that would remain effective for months once applied
Researchers are beginning to identify what compounds make individuals more attractive to mosquitos. That is a first step in the development of a biomarker that could be developed into a clinical laboratory test. Question is: would there be enough consumers wanting to do a lab test to determine if they were highly attractive to mosquitos, thus making this a revenue-generating test for labs?
The SA article reported on their study published in the journal Cell titled, “Differential Mosquito Attraction to Humans Is Associated with Skin-Derived Carboxylic Acid Levels.” The researchers, according to SA, found that individual humans have “a unique scent profile made up of different chemical compounds” and that “mosquitoes were most drawn to people whose skin produces high levels of carboxylic acids.” The researchers also found that “attractiveness to mosquitoes remained steady over time, regardless of changes in diet or grooming habits.”
At a minimum, there would be widespread consumer interest to at least understand why some individuals get more mosquito bites than others. What may be of particular interest to microbiologists is the statement by molecular biologist Omar Akbari, PhD, of the University of California, San Diego, who told Scientific American that by “taking human-colonizing skin bacteria … and engineering them in such a way that they can either express a repellent compound or be able to degrade something that’s attractive,” a mosquito repellant could be developed that would last for months once applied.
“This study clearly shows that these acids are important,” neurogeneticist Matthew DeGennaro, PhD (above), told CNN. “… how the mosquitoes perceive these carboxylic acids is interesting because these particular chemicals … are hard to smell at a distance. It could be that these chemicals are being altered by … the skin microbiome … if we understand why mosquitoes find a host, we can design new repellents that will block the mosquitoes from sensing those chemicals, and this could be used to improve our current repellents.” Clinical laboratory testing will be needed to produce biomarkers for developing such improved repellents. (Photo copyright: Laboratory of Tropical Genetics.)
Clinical Laboratory Testing Needed to Identify Levels of Carboxylic Acids
To complete their study, the researchers had 64 participants wear nylon stockings for six hours on their arms to get their unique scent into the fabric. The scent on the stockings was not discernible to the human nose, but it was to the mosquitos.
Two pieces of the nylon were then placed in a closed container with Aedes aegypti mosquitoes. The researchers found that certain samples were more popular with the mosquitos than others. Upon further analysis the researchers found that the most popular samples came from subjects with higher levels of carboxylic acids, and the least popular had the lowest levels. The scientists ran the test with the same participants several times over three years and the results remained largely the same.
Carboxylic acid is an organic compound found in humans in sebum, the oily layer protecting our skin. The level at which humans release carboxylic acid varies from person to person. And there is no discernible way the human nose can determine whether a person has the level of carboxylic acid on the skin that mosquitos find desirable. The answer would need to be determined by a diagnostic test performed in a clinical laboratory.
Although the development of a test to determine someone’s susceptibility to mosquitos may be far away, there could be significant consumer interest in developing such a test.
“The question of why some people are more attractive to mosquitoes than others—that’s the question that everybody asks,” Leslie B. Vosshall, PhD, Chief Scientific Officer, Howard Hughes Medical Institute, who led the research team to find out why some people are more attractive to mosquitos than others, told Scientific American. “My mother, my sister, people in the street, my colleagues—everybody wants to know.” She credits their interest as the inspiration for embarking on the study.
“Understanding what makes someone a ‘mosquito magnet’ will suggest ways to rationally design interventions such as skin microbiota manipulation to make people less attractive to mosquitoes. We propose that the ability to predict which individuals in a community are high attractors would allow for more effective deployment of resources to combat the spread of mosquito-borne pathogens,” the researchers wrote in their Cell paper.
Preventing Spread of Deadly Diseases
Although mosquitos are an annoyance, they also can be dangerous vectors of disease.
“Every bite of these mosquitoes puts people into public health danger. Aedes aegypti mosquitoes are vectors for dengue, yellow fever, and Zika,” Vosshall told CNN. “Those people who are magnets are going to be much more likely to be infected with viruses.”
Further research into these early findings may help develop diagnostic tests to protect against the spread of these diseases and identify individuals who are more attractive to the mosquitos, and therefore, more likely to contract and spread disease.
Being able to identify which individuals are mosquito magnets could help keep individuals safe from dangerous diseases, and development of a better repellent could also make outdoor summer events more bearable for the (unfortunately) popular among the pests. Medical laboratory tests associated with determining an individual’s susceptibility to mosquito bites could give clinical laboratories a new way to add value to consumers and patients.
Research could lead to clinical laboratory tests in service of precision medicine therapies to reduce a person’s susceptibility to being targeted by blood-sucking insects
Ever wonder why some people attract mosquitoes while others do not? Could biting insects pick their victims by smell? Scientists in California believe the answers to these questions could lead to new precision medicine therapies and clinical laboratory tests.
The research revealed evidence that some blood-sucking insects may identify their prey by homing in on the “scent” of chemicals produced by bacteria located in the skin microbiome of animals and humans.
This is yet another example of research into one area of the human microbiome that might someday lead to a new clinical laboratory test, in this case to determine if a person is more likely to attracts biting insects. If there were such a test, precision medicine therapies could be developed that change an individual’s microbiome to discourage insects from biting that individual.
Then, the clinical laboratory test would have value because it helped diagnose a health condition that is treatable.
Curiosity regarding why mosquitoes seem to gravitate towards some humans over others was the original catalyst for the UCSD Medical School research. “You know when you go to a barbeque and your friend is getting bombarded by mosquitos, but you’re fine? There is some research to support the idea that the difference in mosquito attraction is linked to your skin microbiome—the unique community of bacteria living on your skin,” said Holly Lutz, PhD (above), first author of the UCSD study. “Keeping in mind that some people are more attractive to mosquitoes than others, I wondered what makes insects attracted to some bats but not others.” Lutz’s research could lead to clinical laboratory tests that drive precision medicine therapies to alter human skin microbiomes and make people less attractive to biting insects. (Photo copyright: The Field Museum of Natural History.)
Biting Flies Prefer Specific Bats
“In these caves, I’d see all these different bat species or even taxonomic families roosting side by side. Some of them were loaded with bat flies, while others had none or only a few,” Lutz said in Phys.org. “And these flies are typically very specific to different kinds of bats—you won’t find a fly that normally feeds on horseshoe bats crawling around on a fruit bat. I started wondering why the flies are so particular. Clearly, they can crawl over from one kind of bat to another, but they don’t really seem to be doing that.”
The researchers suspected that the bacteria contained in the skin microbiomes of individual bats could be influencing which bats the flies selected to bite. The bacteria produce a distinctive odor which may make certain bats more attractive to the flies.
The type of fly assessed for the study are related to mosquitoes and most of them are incapable of flight.
“They have incredibly reduced wings in many cases and can’t actually fly,” Lutz explained. “And they have reduced eyesight, so they probably aren’t really operating by vision. So, some other sensory mechanisms must be at play, maybe a sense of smell or an ability to detect chemical cues.”
To test their hypothesis, the research team collected skin and fur samples from the bodies and wings of a variety of bat species located in various caves around Kenya and Uganda. They collected their samples at 14 field sites from August to October in 2016. They then examined the DNA of the bats as well as the microbes residing on the animals’ skin and searched for the presence of flies.
“The flies are exquisitely evolved to stay on their bat,” said Carl Dick, PhD, a professor of biology at Western Kentucky University and one of the study’s authors. “They have special combs, spines, and claws that hold them in place in the fur, and they can run quickly in any direction to evade the biting and scratching of the bats, or the efforts by researchers to capture them,” he told Phys.org.
“You brush the bats’ fur with your forceps, and it’s like you’re chasing the fastest little spider,” Lutz said. “The flies can disappear in a split second. They are fascinatingly creepy.”
Genetic Sequencing DNA of Bat Skin Bacteria
After collecting their specimens, the researchers extracted DNA from the collected bacteria and performed genetic sequencing on the samples. They created libraries of the bacteria contained in each skin sample and used bioinformatics methods to identify the bacteria and compare the samples from bats that had flies versus those that did not.
“How the flies actually locate and find their bats has previously been something of a mystery,” Dick noted. “But because most bat flies live and feed on only one bat species, it’s clear that they somehow find the right host.”
The scientists discovered that different bat families did have their own distinctive skin microbiome, even among samples collected from different locations. They found that differences in the skin microbiomes of certain bats does contribute to whether those bats have parasites. But not all their questions were answered.
“We weren’t able to collect the actual chemicals producing cue—secondary metabolites or volatile organic compounds—during this initial work. Without that information, we can’t definitively say that the bacteria are leading the flies to their hosts,” Lutz said.
Next Steps
“So, next steps will be to sample bats in a way that we can actually tie these compounds to the bacteria. In science, there is always a next step,” she added.
This research illustrates that there may be a reason why certain animals and humans tend to be more attractive to insects than others. It is also possible that an individual’s skin microbiome may explain why some people are more prone to mosquito and other types of insect bites.
More research and clinical studies on this topic are needed, but it could possibly lead to a clinical laboratory test to determine if an individual’s skin microbiome could contribute to his or her potential to being bitten by insects. Such a test would be quite beneficial, as insects can carry a variety of diseases that are harmful to humans.
Perhaps a precision medicine therapy could be developed to alter a person’s microbiome to make them invisible to blood-sucking insects. That would be a boon to regions of the world were diseases like malaria are spread by insect bites.
