By SHIRLEY S. WANG
If you’re one of those people whom mosquitoes tend to favor, maybe it’s because you aren’t sufficiently stressed-out.
Insects have very keen powers of smell that direct them to their targets. But for researchers trying to figure out what attracts or repels the pests, sorting through the 300 to 400 distinct chemical odors that the human body produces has proved daunting.
Now scientists at Rothamsted Research in the U.K. have been making headway at understanding why some people can end up with dozens of bites after a backyard barbecue, while others remain unscathed. The researchers have identified a handful of the body’s chemical odors—some of which may be related to stress—that are present in significantly larger concentrations in people that the bugs are happier to leave alone. If efforts to synthesize these particular chemicals are successful, the result could be an all-natural mosquito repellent that is more effective and safer than products currently available.
“Mosquitoes fly through an aerial soup of chemicals, but can home in on those that draw them to humans,” says James Logan, a researcher at Rothamsted, one of the world’s oldest agricultural-research institutions. But when the combination of human odors is wrong, he says, “the mosquito fails to recognize this signal as a potential blood meal.”
The phenomenon that some people are more prone to mosquito bites than others is well documented. In the 1990s, chemist Ulrich Bernier, now at the U.S. Department of Agriculture’s Agricultural Research Service, began looking for what he calls the “magic compounds” that attract mosquitoes. His research helped to show that mosquitoes are attracted to humans by blends of common chemicals such as carbon dioxide, released from the skin and by exhaling, and lactic acid, which is present on the skin, especially when we exercise. But none of the known attractant chemicals explained why mosquitoes preferred some people to others.
Rothamsted’s Dr. Logan says the answer isn’t to be found in attractant chemicals. He and colleagues observed that everyone produces chemicals that mosquitoes like, but those who are unattractive to mosquitoes produce more of certain chemicals that repel them.
Misguided Mosquitoes
“The repellents were what made the difference,” says Dr. Logan, who is interested in the study of how animals communicate using smell. These chemicals may cloud or mask the attractive chemicals, or may disable mosquitoes from being able to detect those attractive odors, he suggests.
Besides delivering annoying bites, mosquitoes cause hundreds of millions of cases of disease each year. As many as 500 million cases of malaria are contracted globally each year, and more than one million people die from it, according to the Centers for Disease Control and Prevention. Mosquitoes can also spread West Nile virus, dengue fever, yellow fever and other illnesses.
Currently the most effective repellents on the market often contain a chemical known as DEET, which has been associated in some studies with potential safety concerns, such as cancer and Gulf War syndrome. It also damages materials made of plastic. The federal Environmental Protection Agency has determined that DEET, when used as directed, is safe.
The Rothamsted team set out to get the mosquitoes’ viewpoint. The researchers separated human volunteers into two groups—those who were attractive to mosquitoes and those who weren’t. They then put each of the volunteers into body-size foil bags for two hours to collect their body odors. Using a machine known as a chromatograph, the scientists were able to separate the chemicals. They then tested each of them to see how the mosquitoes responded. By attaching microelectrodes to the insects’ antennae, the researchers could measure the electrical impulses that are generated when mosquitoes recognize a chemical.
Dr. Logan and his team have found only a small number of body chemicals—seven or eight—that were present in significantly different quantities between those people who were attractive to mosquitoes and those who weren’t. They then put their findings to the test. For this they used a so-called Y-tube olfactometer that allows mosquitoes to make a choice and fly toward or away from an individual’s hand. After applying the chemicals thought to be repellant on the hands of individuals known to be attractive, Dr. Logan found that the bugs either flew in the opposite direction or weren’t motivated by the person’s smell to fly at all.
The chemicals were then tested to determine their impact on actual biting behavior. Volunteers put their arms in a box containing mosquitoes, one arm coated with repellent chemicals and the other without, to see if the arm without the coating got bitten more.
Significant Repellency
The group’s latest paper, published in March in the Journal of Medical Entomology, identified two compounds with “significant repellency.” One of the compounds, 6-methyl-5-hepten-2-one, is a skin-derived compound that has the odor of toned-down nail-polish remover, according to George Preti, an organic chemist at the Monell Chemical Senses Center in Philadelphia, who is involved in a separate line of research into insect-biting behavior. The other, identified in the paper as geranylacetone, has a pleasant odor, though there is some question about whether the chemical is formed by the human biochemical process or is picked up in the environment, Dr. Preti says.
Dr. Logan declined to comment about the specific chemicals because of proprietary concerns. He says the findings have been patented and the group is working with a commercial company to develop the compounds into a usable insect repellent. One issue that still needs to be resolved: how to develop a formulation of the repellent chemicals that will stay on the skin, rather than quickly evaporating as they do naturally. The hope is to get a product to market within a year or two, he says.
Some of the chemicals researchers identified are believed to be related to stress, Dr. Logan says. Previous research has shown that these particular chemicals could be converted from certain other molecules and this could be as a result of oxidation in the body at times of stress, he says. However, it’s not clear if the chemicals observed by the Rothamsted researchers were created in this way, and research is continuing to answer this and other questions.
Dr. Logan suggests that mosquitoes may deem hosts that emit more of these chemicals to be diseased or injured and “not a good quality blood meal.” Proteins in the blood are necessary for female mosquitoes to produce fertile eggs, and Dr. Logan says it might be evolutionarily advantageous for mosquitoes to detect and avoid such people.
Other Research
Other research includes an effort by scientists at the University of California, Riverside, who published a paper in the journal Nature last week identifying a recently discovered class of molecules that inhibit fruit flies’ and mosquitoes’ ability to detect carbon dioxide. Mosquitoes can detect carbon dioxide emissions from long ranges, so turning off the ability to detect the gas, perhaps by releasing the inhibiting molecules into the environment, may be a way of keeping the bugs at bay, the researchers suggest. Another team, at the Monell Chemical Senses Center, is launching a study into whether the taste of human skin and blood are related to the insects’ interest in biting certain individuals.
What Is High Blood Pressure?
High blood pressure (HBP) is a serious condition that can lead to coronary heart disease, heart failure, stroke, kidney failure, and other health problems.
“Blood pressure” is the force of blood pushing against the walls of the arteries as the heart pumps out blood. If this pressure rises and stays high over time, it can damage the body in many ways.
About 1 in 3 adults in the United States has HBP. HBP itself usually has no symptoms. You can have it for years without knowing it. During this time, though, it can damage the heart, blood vessels, kidneys, and other parts of your body.
This is why knowing your blood pressure numbers is important, even when you’re feeling fine. If your blood pressure is normal, you can work with your health care team to keep it that way. If your blood pressure is too high, you need treatment to prevent damage to your body’s organs.
Blood Pressure Numbers
Blood pressure numbers include systolic (sis-TOL-ik) and diastolic (di-a-STOL-ik) pressures. Systolic blood pressure is the pressure when the heart beats while pumping blood. Diastolic blood pressure is the pressure when the heart is at rest between beats.
You will most often see blood pressure numbers written with the systolic number above or before the diastolic, such as 120/80 mmHg. (The mmHg is millimeters of mercury—the units used to measure blood pressure.)
Blood pressure tends to rise with age. Following a healthy lifestyle helps some people delay or prevent this rise in blood pressure.
People who have HBP can take steps to control it and reduce their risks for related health problems. Key steps include following a healthy lifestyle, having ongoing medical care, and following the treatment plan that your doctor prescribes.
Genetic and environmental influences
An international research team has identified common genetic variants associated with systolic blood pressure, diastolic blood pressure, and high blood pressure (hypertension), suggesting potential avenues of investigation for the prevention or treatment of high blood pressure.
About 1 in 3 adults (approximately 72 million people) in the United States has high blood pressure. High blood pressure can lead to coronary heart disease, heart failure, stroke, kidney failure, and other health problems, and causes over 7 million deaths worldwide each year.
While the environment (diet, physical activity, stress, etc.) affects blood pressure, genetics also plays a substantial role and may increase some people’s risk of developing high blood pressure under specific environmental exposures; however, many genes involved in blood pressure regulation remain unknown.
To identify genes involved in blood pressure maintenance and high blood pressure, the researchers analyzed differences in the genomes of nearly 30,000 people of European descent whose average systolic blood pressures ranged from 118 mm Hg to 143 mm Hg and average diastolic blood pressures ranged from 72 mm Hg to 83 mm Hg. These individuals were part of a long-term study of cardiovascular health and disease supported by the National Institutes of Health called ARIC (Atherosclerosis Risk in Communities). The researchers looked for genetic differences that correlated with high blood pressure and found 11 variations or changes in DNA sequence that appear to regulate blood pressure levels.
Blood pressure is measured in millimeters of mercury (mm Hg), and expressed with two numbers, for example, 120/80 mm Hg. The first number (systolic pressure) is the pressure when the heart beats while pumping blood. The second number (diastolic pressure) is the pressure in large arteries when the heart is at rest between beats.
The researchers found that the top 10 gene variants for systolic and diastolic blood pressure were each associated with around a 1 and 0.5 mm Hg increase in systolic and diastolic blood pressure, respectively. The prevalence of high blood pressure increased as the number of variants increased.
People who carry very few blood pressure genetic risk variants have blood pressure levels that are several mm Hg lower than those who carry multiple risk variants. In practical terms this is enough to increase the risk for cardiovascular disease. A prolonged increase in diastolic blood pressure of only 5 mm Hg is associated with a 34 percent increase in risk for stroke and a 21 percent increase of coronary heart disease. The new insight into how the kidneys govern the balance of salt in the body, a crucial task for regulating blood pressure. And, it reveals how a gene already linked to behavior and mental health can play a role in the body, as well as the brain.
Take a Blood Pressure at Home
Knowing your blood pressure is a good idea because it shows how at least in part how healthy your lifestyle is. Some people have high BP genetically but good exercise and diet habits can help lower it. First, you need to know the normal healthy ranges of an adult blood pressure. The standard healthy B/P as of now is 120 systolic / 80 diastolic. The systolic pressure measures how hard the left ventricle pumps during systole (contraction phase) and the diastolic pressure measures how much the heart relaxes during diastole (relaxation phase). To take a blood pressure, you’ll need a blood pressure cuff and a stethoscope. In order to get an accurate reading, you must make sure that the edge of the cuff is 40% of the circumference of the person’s arm between the inner elbow and the shoulder. If this isn’t the case, the reading can be a false high or a false low.
PLASTINATION
Invented by Dr Gunther von Hagens in 1977 at the University of Heidelberg in Germany, plastination involves replacing the body’s fluids and fat with reactive plastics, thus retaining all tissue structures. The technique takes up to 5000 hours for a full-body plastinate. After the first stage, the polymer is still pliable and the body can be shaped into poses. The body is sealed in plastic and a gas is pumped in that hardens the polymer, forming a rigid plastinate that will last indefinitely.
It’s time to look deep inside yourself and see what you are like under the surface. Underneath your clothes, your hairstyle, your skin. The Amazing Human Body exhibition does exactly that. If you’ve ever wondered what your liver looks like, considered your cruciate ligament or pondered your pancreas.
Using a technique pioneered in the 1970s by Germany’s Dr Gunther von Hagens, the exhibition features real human bodies and body parts that have been “plastinated” – literally preserved in plastic. The bodies Sydney will see came from the Tianjin Natural History Museum and the Dalian Medical University’s Institute of Plastination in China.
This is the ultimate anatomy lesson. Displays in the exhibition, which features about 400 specimens including 20 full-body plastinates and individual organs, are divided by the systems of the body – locomotion (skeletal and muscular), nervous, alimentary/digestive, cardiology, respiratory, pre-natal, reproductive and endocrine. Event manager Wayne Castle says,
“It’s the first time members of the public can see what has previously been the domain of medical practitioners.”
And he’s right. Books, models, photographs and drawings can’t show this level of detail. Castle expects that as well as the general public the show will attract those in the industry keen for an incredible learning experience, such as medical students – including physiotherapists, forensic scientists and nurses – medical researchers, sporting groups and even artists.
“It’s interesting because it shows you what your body looks like in everyday poses, doing normal activities, but from an anatomical perspective,” says Joshua Pike, a registered nurse at Royal Prince Alfred Hospital.
Everyone who attends the exhibition will have an immediate point of reference: themselves. Although some may be squeamish about making the correlation, Castle says,
“It’s a way of appreciating your own body. Most people know what’s under the bonnet of a car but have no clue what’s underneath their own skin. Finally seeing that, in terms of knowing how to look after yourself, is astounding.”
The exhibition is set up so people can choose their level of involvement. Student groups can arrange for an audiovisual presentation before entry. Inside, display boards carry in-depth, detailed descriptions of what’s being shown.
“It’s almost like a medical textbook,” Castle says.
Even if you’re not much of a reader, there is plenty to be gleaned by just being there. One of the most impressive displays is an entire body cut into one-centimetre “slices” that stretches 14 metres long and shows a fascinating cross-section of the lungs and chambers of the heart. Perhaps the most intricate piece is a cast of the entire blood vessel system in the arm, from above the elbow right down to the fingertips.
As to what the full-body plastinates are like “in the flesh”, they look both more real and somehow more fake than expected. In various skin-coloured tones, from wan yellow to deep pink, some have veins and vessels dyed red and blue for ease of identification. Their skin is delicate, glistening in parts and malleable like waxy paperbark where it has been stripped away from the body. Close up, the models smell like old candles.
The show has sparked some controversy over the ethical implications of putting real human corpses on display. While Castle disagrees with the critics, stressing the educational and health-awareness benefits of the exhibition, it is confronting and probably will upset some attendees. According to the organisers, all bodies that feature in The Amazing Human Body were donated willingly for the purpose.
Shock tactic
Event organiser Wayne Castle says perhaps the most confronting part of the Amazing Human Body exhibition is the display of “normal” lungs compared to a smoker’s lungs.
In fact, most of the lungs you will see at the show are smokers’ lungs – the effects are easily spotted. Castle claims that at a similar Body Worlds exhibition in Britain, an exit survey showed 9 per cent of smokers who viewed this display quit the cancer sticks.
“No other anti-smoking campaign has ever had that kind of success,” he says.
Other nasties on display in the pathology section of the exhibition are ovarian tumours, bleeding of the cerebellum, a heart that has had a cardiac arrest, stomach cancer, a liver hardened by alcoholism, a uterine tumour and hardening of the arteries.
