Sunday March 31, 2019
PAGE 51
Kaieteur News
Mosquitoes Sniff Out Human Sweat To Find Us Mosquitoes searching for a meal of blood use a variety of clues to track down humans, including our body heat and the carbon dioxide in our breath. Now, research shows that a certain olfactory receptor in their antennae also serves as a detector of humans, responding to smelly chemicals in our sweat. Targeting this receptor might offer a new way to foil blood-seeking mosquitoes and prevent the transmission of diseases including malaria, Zika virus and dengue, according to the study published Thursday in the journal Current Biology. “We found a receptor for human sweat, and we found that acidic volatiles that come off of us are really key for mosquitoes to find us,” says Matthew DeGennaro, a neurogeneticist at Florida International University in Miami. “I think what’s exciting about it is that finally we have evidence that there is some sort of pathway, in the sense of smell, that is required for mosquitoes to like us,”
says Lindy McBride, a scientist at Princeton University who studies mosquito behavior and was not part of the research team. It’s long been known that mosquitoes rely on multiple clues to target humans. First, a mosquito will sense exhaled carbon dioxide from a distance that can be more than 30 feet. “After the carbon dioxide,” DeGennaro explains, “then it begins to sense human odor.” The mosquito follows this odor and, when it gets very close, starts to detect body heat. Once mosquitoes land on you, “they actually can taste your skin with their legs and then they look for a place to bite,” DeGennaro says. He and his colleagues genetically altered mosquitoes to block the activity of a specific olfactory receptor called Ir8a. The result was that female mosquitoes — which are the ones that suck blood — were no longer attracted to lactic acid, an important component of human sweat. What’s more, the team did a variety of lab tests to see if
disrupting this receptor would make mosquitoes less responsive to humans. T he scientists asked people to put their hands into a device called an “olfactometer” that let mosquitoes smell them from a distance. Captive mosquitoes could fly through the device to get close, but not close enough to bite. Tests showed that genetically altering mosquitoes to disable this olfactory receptor made the pests significantly less likely to fly toward the humans’ skin. And to show that it was a response to smell that was being affected, the researchers also had people in the study wear nylon sleeves for about 12 hours to collect sweat. Then they put these sleeves into the olfactometer. Again, mutant mosquitoes were much less attracted to the scent than normal mosquitoes were. Now, it might seem obvious that crippling mosquitoes’ olfactory system would make it difficult for them to smell people. “But the
Keto diet: New study unearths sex differences
In recent years, the ketogenic diet has become increasingly popular with people who want to lose weight quickly. A new study asks whether this dietary pattern works as well in females as it does in males. Experts originally designed the ketogenic diet, which people often refer to as the keto diet, as a treatment for epilepsy. Today, people more commonly use it to increase weight loss or to help control their type 2 diabetes. The keto diet allows a liberal consumption of fats and an adequate amount of protein but heavily reduces the intake of carbohydrates, such as starch, sugar, and fiber. Usually, the body burns carbohydrates as its primary source of energy. However, if there are none available, it switches to burning stored fats. As part of this process, which is called ketosis, the liver turns fatty acids into molecules called ketone bodies. KETO SEX DIFFERENCES Although there is evidence that the keto diet might offer some benefits for certain people, there is much debate surrounding this diet and its long-term effects. A recent study brings into question whether the keto diet provides the same benefits for females as it does for males. A new study using mouse models focused on sex differences in relation to the keto diet. The researchers, who are from the University of Iowa in Iowa City, presented their findings at the ENDO 2019 conference in New Orleans, LA. Senior investigator Dr. E. Dale Abel, Ph.D., chair of the University of Iowa Department of Internal Medicine explains the issue: “Most studies of the ketogenic diet for weight loss have taken place in small numbers of patients or in only male mice, so sex-based differences in response to this diet are unclear.” To investigate, Dr. Abel and research
assistant Jesse Cochran fed male and female mice either a ketogenic diet or a standard diet. The keto diet comprised 75 percent fat, 3 percent carbohydrates, and 8 percent protein by mass, while the control diet consisted of 7 percent fat, 47 percent carbohydrates, and 19 percent protein. After 15 weeks, the researchers found that the male mice on the keto diet maintained blood glucose control and lost body weight. The female mice, however, gained weight. These female mice also had poorer blood sugar control compared with the female mice that ate a standard diet. According to the authors, “[they] developed impaired glucose tolerance.” The researchers believe that this stark difference might be due, at least in part, to the primary female sex hormone — estrogen. To investigate, they removed the ovaries of some of the female mice and ran a similar experiment. Doing this changed the results substantially. Compared with mice that received a control diet, female mice without ovaries that consumed a keto diet showed a decrease in body fat, and they also maintained blood glucose control. In other words, without estrogen, the keto diet worked. Cochran explains, “This finding suggests that postmenopausal women could potentially experience better weight loss outcomes with the ketogenic diet compared to younger women.” However, the researchers make it clear that it is important to speak with a doctor before embarking on the keto diet. This study is one of very few to investigate potential sex differences in the effectiveness of the keto diet. However, the study used an animal model, so scientists will still need to carry out investigations in humans before we can reach any solid conclusions. (https:// www.medicalnewstoday.com/articles/ 324792.php)
thing is, mosquitoes smell in a couple of different ways,” McBride says. Previous work showed that disabling a different part of the olfactory system “had no effect, and it was a big surprise,” she notes. “So it’s really exciting to see that this other type of smelling is actually essential.” “I thought this was a fantastic study,” says Jeff Riffell, a biologist at the University of Washington who studies chemical communication. “It’s an open question about how mosquitoes, No. 1, can locate people to bite. And then, how do they choose which people to bite — what are the mechanisms?” Riffell says this study shows conclusively that the behavior is mediated by a receptor that allows the mosquitoes to “smell our, you know, kind of funk or body odor. And so they’re able to really demonstrate the importance of this receptor.” It might be possible, he says, to create “a perfume or a chemical that prevents that receptor from operating. So you can imagine it being like a perfume or something you sprayed on, and mosquitoes can no longer kind of detect our sweat.” Laura Duvall of The Rockefeller University in New York, who studies hostseeking behavior in mosquitoes, says this research might also help explain how mosquitoes distinguish between humans and other animals. “Mosquitoes are so good
at finding us because they’re paying attention to many different components of human odor — including the acidic volatiles that we produce,” she notes. Disrupting any one single pathway isn’t likely to prevent mosquitoes from biting us, Duvall says. But understanding all the signals that the insects use could help “make better human mimics, which could be used to lure mosquitoes into a trap — and away from humans.” Larry Zwiebel, a biologist who studies insect olfaction and behavior at Vanderbilt University, says evolution has created a sensory system for mosquitoes that has lots of parts that overlap and interact to produce the most efficient human-seeking machine. He says some of the lab tests in this study, for example, made it clear that carbon dioxide was necessary for sensitizing mosquitoes to lactic acid in human sweat. “So it shows that in order for this process to really work effectively, and at its highest level, the mosquito wants to sense carbon dioxide, and that information makes the
lactic acid information more valuable to the mosquito — more usable,” Zwiebel says. “The mosquito is looking for what is often called a coincidence detector,” he says. “It’s not just one signal, but many signals — all of which, when they coincide, provide the strongest degree of impulse to drive this behavior.” Finding ways to overstimulate parts of the mosquito’s human-detection system, Zwiebel says, might help scientists create a particularly powerful repellent. For the mosquito, he says, the effect would be “like getting on an elevator with someone who has put on way too much cologne.” (https:// w w w. n p r. o r g / s e c t i o n s / health-shots/2019/03/28/ 706838786/how-mosquitoessniff-out-human-sweat-tofind-us)