Follow the Odor and CO2: Flight Patterns Reveal How Mosquitoes Find Hosts to Transmit Deadly Diseases

An Aedes aegypti mosquito prepares to bite a human. (Credit: Image courtesy of USDA.)

Science Daily  — The carbon dioxide we exhale and the odors our skins emanate serve as crucial cues to female mosquitoes on the hunt for human hosts to bite and spread diseases such as malaria, dengue and yellow fever.

The researchers report in the Oct. 15 issue of the Journal of Experimental Biology that puffs of exhaled carbon dioxide first attract these mosquitoes, which then proceed to follow a broad skin odor plume, eventually landing on a human host.Two entomologists at the University of California, Riverside have now performed experiments to study how female Aedes aegypti -- mosquitoes that transmit yellow fever and dengue -- respond to plumes of carbon dioxide and human odor.

The results from the study by Ring Cardé, a distinguished professor of entomology at the University of California, Riverside, and Teun Dekker, formerly a graduate student in Cardé's lab and now an assistant professor at the Swedish University of Agricultural Research, could clue scientists on how odors can be used in traps for intercepting and capturing host-seeking mosquitoes.

Yellow fever is a viral disease that causes 30,000 deaths worldwide each year. Dengue, another viral disease, infects 50 to 100 million people worldwide a year, leading to half a million hospitalizations, and 12,500,000 deaths.

In the lab, the researchers released female yellow fever mosquitoes into a wind tunnel they built, and filmed their flight paths. They found that:

• Mosquitoes head upwind only briefly when they encounter just a whiff of carbon dioxide but proceed continuously upwind when the carbon dioxide plume is turbulent, fluctuating in concentration and mimicking the presence of a live host.
• Mosquitoes' orientation to human skin odor, in contrast, is optimal when the plume of skin odor is broad and unvarying in its intensity, as would occur when a mosquito closes in on a potential host.

"Carbon dioxide induces a faster and more direct upwind orientation than skin odor," said Cardé, who holds the Alfred M. Boyce Chair in Entomology. "Our experiments show that the response of yellow fever mosquitoes to skin odor requires an exposure longer than that of carbon dioxide to induce upwind flight."

Dekker and Cardé also report that the dynamics -- response time, duration and speed -- of carbon dioxide-induced upwind surging were very similar across a wide range of carbon dioxide concentrations, from 100 to 0.05 percent (barely above atmospheric levels).

"The mosquitoes' carbon dioxide receptors allow the insects to respond almost instantly to even the slightest amount of the gas," Cardé said. "Carbon dioxide alone attracts these mosquitoes and does not require assistance from other odors. Skin odors, however, become important when the mosquito is near the host, selecting biting sites. Further, the mosquitoes' sensitivity to skin odors increases 5- to 25-fold after 'priming' with a whiff of carbon dioxide."

The research project was supported by grants to Cardé from the University of California Systemwide Mosquito Research Program and the Office of Naval Research -- DARPA Plume Tracing Program; to Dekker, the research paper's first author, from Insect Chemical Ecology, Ethology and Evolution (ICE³) Linnaeus and the Swedish Research Council FORMAS.

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Regular exercise improves health of people with long-term kidney disease

 by Biomechanism 

There are many reasons why people with chronic kidney disease (CKD) often lose fitness and have increasing difficulty performing normal daily tasks, but new research shows scientific evidence for the benefits of regular exercise for people with CKD, including those with a kidney transplant. They can improve their physical fitness, walk further, have healthier blood pressures, healthier heart rates, higher health-related quality of life scores and better nutritional characteristics compared to those who don’t exercise. So concludes a systematic review published in The Cochrane Library.

CKD is a worldwide public health problem and a person is said to have CKD if they have damaged or poorly performing kidneys where the effects last for more than three months. There are many causes of damage, including high blood pressure, diabetes and rheumatic diseases. “Their muscles tend to tire quickly, which reduces the amount of exercise they do, but this then further reduces their fitness,” explains Susanne Heiwe from the Karolinska Institute in Stockholm, Sweden.

During the last 30 years there have been many studies into the way that exercise affects people with CKD, but very few evidence-based guidelines have been drawn up. To fill this gap Heiwe and her colleague, Stefan Jacobson, studied the data and results in forty-five studies that met specific inclusion criteria. Together these involved a total of 1,863 participants.

Heiwe’s team discovered adults with CKD but who do not yet need dialysis, patients on dialysis and kidney transplant recipients all benefitted from exercise, but different types of exercise produced different types of benefit.

For example, when compared with controls, people who performed supervised, high intensity, cardiovascular training for four to six months had significantly improved aerobic capacity Other studies showed that three months of regular, high intensity resistance training or yoga, whether supervised or not, increases muscular strength and, when supervised, the high intensity resistance training also increases walking capacity over a three month period.

“More research is needed so we can discover how to set up exercise programs that get the desired outcome as efficiently as possible,” says Heiwe, who believes that the Cochrane review will help renal health-care providers prescribe exercise training more often and make evidence-based choices about which type of exercise to recommend.

So far most of the studies have looked at the effects of cardiovascular exercise programmes. “We now need to know more about the effects of resistance training or mixed cardiovascular and resistance training,” says Heiwe.