Who Gets More Mosquito Bites Why some people are itching and scratching while others seem unaffected

Why do some people attract mosquito bites more than others? Heidi Mitchell explains on Lunch Break.

It is peak mosquito season, and while some lucky outdoor venturers seem unperturbed by the tiny insects, others appear to be relentlessly assaulted. Scientists are trying to understand what makes certain humans more attractive to the bugs. One expert, molecular vector biologist L.J. Zwiebel, a professor of biological sciences at Vanderbilt University, weighs in.

Sweet Smell of Success

Mosquitoes find their mammalian prey through sensing the heat and carbon dioxide mammals emit. Pregnant women and larger people are sometimes the victim of multiple attacks, since they exert more energy than the average person.

Mosquitoes are also guided by their sense of smell. "Despite what my grandmother told me, I don't have sweet blood," says Dr. Zwiebel, since mosquitoes cannot distinguish blood quality. "Mosquitoes are attracted to our human odor, and that is largely a consequence of the bacteria on our skin," says Dr. Zwiebel. The "flora and fauna on our skin" also smell appetizing to mosquitoes, says Dr. Zweibel, and these can increase when we sweat or spend a lot of time outdoors.

As far as Dr. Zwiebel knows, there is no scientific basis to prove that having high cholesterol or diabetes, despite what some websites claim, will keep bugs away. Nor will taking vitamin B supplements, eating garlic or taking specific medications.

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A culex quinquefasciatus mosquito.

After 20 years in labs with the biting bugs, Dr. Zwiebel says he can stick his arm into a container of mozzies and be bit hundreds of times, yet "not have a hair out of place." Children, who have been bitten far fewer times than adults, may have stronger reactions to bites, since their immune systems haven't matured fully. But adults who are convinced they are being victimized by the bloodsuckers usually are not. "There are some people who have strong allergic responses to the bites which may make it seem like they're being bit more often, but they're probably not," Dr. Zwiebel notes.

Fighting Back

For people covered in welts and itchy wounds, Dr. Zwiebel says to stop scratching: When the mosquito bites, it leaves behind some of its saliva, a substance that contains anticoagulants and a local anesthetic, among other things. The body recognizes it as a foreign invader and sends histamines in to counterattack. Scratching just spreads the saliva and encourages the release of more antibodies, and more itching—a vicious cycle.

Those who swell up and itch a lot when bitten "should speak with their doctor about taking an over-the-counter antihistamine daily as a precaution," says Dr. Zwiebel. The bugs will still bite, but you may not notice, since the drug prevents the allergic response that turns a painless bite into an itchy nuisance.

Cleaner Is Meaner

Female mosquitoes are driven to bite you as they need a blood meal to complete their reproductive cycle and produce fertile eggs, which takes a huge boost of protein. To reduce the chances of being bitten, wash with an antibacterial soap to reduce the volume of mosquito-attracting bacteria on your skin.

Other ways to dodge bites: Avoid the outdoors at dawn and dusk, when mosquitoes are most active. Set up an outdoor fan to shoo bugs away. And wear long trousers and shirts if it's not too hot. Dr. Zwiebel also suggests spraying your clothing with repellent that contains DEET, a chemical that acts to confuse the mosquito's olfactory receptors. "It works, and until something better comes along, it's the best thing available to prevent bites," he says.

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West Nile virus outbreaks will flare up, experts say

West Nile virus outbreaks are likely to flare up in the coming years, spurred on by warmer, longer mosquito seasons coupled with cuts in disease-control funding that leave authorities unprepared, according to two new studies.

After an all-time high in 2003 with nearly 10,000 cases and 264 dead, the virus backed off gradually for the remainder of the decade — until last year. In 2012, there were 5,674 cases and 286 deaths, almost twice the 2003 mortality rate.

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Resurgence of the West Nile virus in 2012 was an unpredictable outbreak.

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West Nile virus likely to flare up in coming years, experts say

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Longer mosquito seasons and less funding to control the disease can lead to a resurgence, studies say.

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This strong resurgence is suggestive of “unpredictable local and regional outbreaks” to come, according to a study by the Centers for Disease Control and Prevention. Even when the number of infections dies down, the virus remains in circulation with an ever-present danger of periodic recurrences.

“Every once in a while, you will have the right conditions to have it build up in the mosquito and bird populations, and spill over to humans,” said Stephen M. Ostroff, formerly of the CDC, who wrote an editorial in the Journal of the American Medical Association (JAMA) that accompanied the studies.
“Our sense of urgency and the degree of attention paid to West Nile virus has diminished considerably and so, too, have the necessary resources to prevent another outbreak,” Ostroff said.
Two studies — a review of the West Nile virus from the CDC and an investigation of a 2012 West Nile epidemic in Dallas from Dallas County Health and Human Services — were published online Tuesday in JAMA, along with the editorial by Ostroff. The Dallas investigation studied 173 cases of West Nile neuroinvasive disease, 225 cases of West Nile fever and 19 deaths in the latter half of 2012.

Transmitted mostly by mosquitoes that have bitten infected birds, the virus made its first U.S. appearance in 1999.

The Dallas study cites the combined effect of a mild winter, the early arrival of spring and summer heat, and lots of rain that caused mosquitoes to hang around for longer than usual, allowing more infection to spread.

Meanwhile, funding toward prevention and control has fallen. The CDC’s Epidemiology and Laboratory Capacity for Infectious Diseases program — which distributes money to states and large cities for use against mosquito-borne diseases — saw its funding drop from nearly $35 million in the early 2000s to less than $10 million by 2012.

Ostroff, the former deputy director of the CDC’s National Center for Infectious Diseases, believes it is a result of growing apathy toward the West Nile virus.

“It seemed like the problem had gone away, and it was an easy place to cut,” he said.
Complacency arises from a belief that a disease is on its way out, but that attitude can be dangerous because some diseases follow more of a boom-and-bust pattern. For instance, experts in the late 1980s thought that tuberculosis could be virtually eliminated from the United States by 2010. An unexpected resurgence of TB a few years later, largely fueled by the onset of the HIV epidemic, hit hard — particularly since funding and TB control programs had been eliminated.

While many states keep an eye out for West Nile infections in humans, the CDC study stresses that early detection in the carriers themselves is key. To wait for people to become exposed to the virus, have it manifest as an infection or illness, visit a doctor and test positive for West Nile virus could cause authorities to lose weeks in the war against an outbreak.

On the other hand, mosquito traps and tests are inexpensive and certainly cheaper than some of the last-resort measures eventually used to bandage up situations such as the Dallas outbreak. The study cited costs of $1.6 million for aerial pesticide spraying and $8 million in estimated West Nile-related health-care costs.

By cutting funding for mosquito surveillance, “we’re being penny-wise and dollar-foolish,” Ostroff said.

If an infection problem is identified early, authorities can try to prevent swarms of mosquitoes from reaching human hosts by draining blocked streams, introducing predatory fish and applying larvicides to prevent spring hatching.

No human vaccine or specific treatment exists. Wearing bug spray does reduce one’s risk of West Nile virus, but the CDC study said people are unlikely to put on repellant regularly, even during well-publicized outbreaks. Advice to wear long pants and sleeves is also unlikely to be followed, especially in the sweltering heat of peak mosquito season.

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Sacramento County reports first 2013 human death of West Nile virus

 

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Sacramento County is reporting California's first human death in 2013 from West Nile virus, a disease spread by bites from infected mosquitoes.

 

The Sacramento County man tested positive for the virus earlier this year, the state Department of Public Health said.

"His illness, as well as his laboratory test results, are potentially consistent with West Nile neuroinvasive disease," the department reported on its website, westnile.ca.gov.

No other county has reported any human cases, whether infected or deceased. The Sacramento County victim's identity is not being released because of health privacy laws.
But the agency known for its "Fight the Bite" campaign reported last week that it has detected the first signs of West Nile virus in dead birds and mosquito samples in the Sacramento region.
Two dead birds, plus two mosquito samples, were found to be carriers of the disease at the Sacramento County Public Health Laboratory, according to the Sacramento-Yolo Mosquito and Vector Control District.

Other counties – Merced, Los Angeles, Fresno, Orange, Ventura and Yuba – already had reported the presence of the virus in a total of 10 dead birds.
In Sacramento County, the birds and mosquitoes were collected over a widespread area, so there's no reason to worry that a particular neighborhood is at risk, officials said.
"Finding the first positive birds is always significant because it provides an early warning sign for the disease," said District Manager David Brown.
At this point, the district does not have plans to immediately begin targeted spraying of pesticides within neighborhood areas.

Symptoms of the virus, caused by a bite from an infected mosquito, include fever, headaches, neck stiffness and body aches.
In severe cases, the virus may lead to stupor, coma, tremors, convulsions, muscle weakness and paralysis. The worst cases can lead to hospitalization from encephalitis, or inflammation of the brain, as was the case with the Sacramento victim.
While it has been known that the disease may contribute to long-term nerve and brain damage, researchers have begun looking into whether West Nile virus may also damage the kidneys.
Fortunately, most people infected with the virus will have no symptoms, according to the federal Centers for Disease Control and Prevention.

About one in five people with the virus develops a fever with other symptoms, the CDC said. Less than 1 percent of infected people develop serious, sometimes fatal, neurologic illness.
Last year, California saw 479 human West Nile virus cases, with 20 deaths. Full story

Read more here: http://www.sacbee.com/2013/06/09/5482701/sacramento-county-reports-first.html#storylink=cpy

 

Smelly feet drive malaria-infected mosquitoes wild

Mosquitoes infected with the malaria parasite are more attracted to the smell of sweat than uninfected insects, a new study finds.             

           

Photo: Zhiltsov Alexandr/Shutterstock

 

Parasites can be cunning little organisms; not only do they live on and feed from their hosts, but they can manipulate the behavior of the hosts to further their cause. For example, scientists have previously confirmed that mosquitoes infected with the clever malaria parasite want longer and more frequent blood meals than non-infected mosquitoes, better facilitating parasite transmission from mosquito to human.

 

And now a team led by Renate Smallegange of Wageningen University and Research Center in the Netherlands has found another way the malaria parasite bewitches its host; it lures them to the smell of human sweat.

 

Describing the interaction of mosquito Anopheles gambiae sensu stricto with the malaria parasite, Plasmodium falciparum as “one of the most important interactions in the context of humanity, with malaria causing over 200 million human cases and over 770 thousand deaths each year,” the researchers set out to demonstrate how the parasite alters mosquito behavior in response to olfactory stimuli.

 

And what better place to start than with a stinky sock?

 

A volunteer wore a nylon stocking for 20 hours; the fragrant sock was then introduced into a cage with both infected and non-infected mosquitoes. The malaria-infected mosquitoes performed significantly more landings and probing attempts in response to human odor than the uninfected mosquitoes — three times as frequently in fact. This “suggests that malaria-infectious females are more attracted to human odors than uninfected mosquitoes,” write the authors of the report that was published in PLOS ONE.

 

It remains unclear how the parasite manipulates mosquitoes’ sense of smell, or which part of human odor is most seductive to the mosquitoes. Uncovering that information could help researchers develop traps to catch infected mosquitoes, the scientists say.

 

But nonetheless, the study sheds important light on how malaria infects so many people.

 

“The results of our study provide vital information that could be used to provide better predictions of how malaria is transmitted from human being to human being by An. gambiae s.s. females,” the authors conclude.

 

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Gallinippers: Mega mosquito may invade central Florida this summer

 

This photo from the University of Florida's Institute of Food and Agricultural Sciences shows the size difference between the invasive gallinipper mosquito and a native species

If you hate mosquitoes now, just wait until you see the size of the ones that may be swarming this summer.

Bug experts from the University of Florida say a species of mega-mosquito called a "gallipper" could invade central Florida as flood waters from tropical storms force the larvae to hatch.
They say these critters are 20-times the size of a typical mosquito, and they pack a painful bite.

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How hacking a mosquito's heart could eradicate malaria

The bioterrorists of the insect world, mosquitoes can transmit a range of deadly diseases after a blood meal. But how do they carry dangerous pathogens like malaria and yellow fever without becoming infected themselves?

Now Julián Hillyer from Vanderbilt University in Nashville, Tennessee, and colleagues are discovering that mosquitoes use a two-pronged trick to intercept infectious agents during their journey from their gut to their salivary glands, from where the pathogens are transmitted to other animals. When a disease passes through a mosquito's heart, it must resist the rapid-flowing bloodstream while, at the same time, immune cells surround the area and launch their attack.
In this video, you can watch a mosquito fight off E. coli. The initial view reveals the insect's peculiar heart, which mostly pumps blood in one direction, towards the head. Immune cells are triggered as the intruding pathogen passes through the organ, usually eliminating most of the disease and keeping the mosquito healthy.

This new understanding of the mosquito immune system could help develop new ways of controlling the spread of disease. "Perhaps we can find ways to augment those immune responses," says Hillyer, suggesting that the disease-filtering process could be improved to completely prevent mosquitoes from transmitting pathogens.

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Jurasic Park for Real? Two Ancient Mosquito Species Discovered

They may contain the blood of an anchient animal and it may be a dinosaur! Holy Jurassic Park batman...

An international team of paleontologists has identified two ancient species of mosquitoes from so-called compression fossils found in the Kishenehn Basin, northwestern Montana, the United States.

Culiseta kishenehn, left, and Culiseta lemniscata (Harbach RE et al / Zootaxa)

Ancient mosquitoes are very rare and the total number of species identified is now 26.
The newly identified species, called Culiseta kishenehn and Culiseta lemniscata, lived on Earth during the Eocene epoch about 46 million years ago. They are the first compression fossils identified from the genus Culiseta. They are produced in rock that is compressed over time, often creating animal fossils that are distorted, unlike the body fossils you get with amber where the whole body is often nicely preserved.

The team was able to spot minute details that distinguish one mosquito species from another, such as wing veins from 0.5 to 1.5 mm long, to minuscule setae, the hair-like structures near the base of the wing.

But is it possible that these fossil mosquitoes from the time of the Eocene epoch could also contain blood?

“Compression fossils are generally less informative morphologically than specimens preserved in amber,” said Dr Ralph Harbach of the Natural History Museum in London, lead author of a paper reporting the new species in the journal Zootaxa. “It is probably less likely for blood to be detected in compression fossils, but it should be possible.”

Blood has already been found in fossil mosquitoes of a similar age to the new finds. A species in the genus Culex preserved in 45-15 million-year-old Dominican amber had blood that contained bird malaria parasites. Some scientists think that human malarial parasites, which are transmitted by the Anopheles mosquitoes, arose by transfer from birds to humans.

And it was in another amber fossil that the oldest fossil mosquito, Burmaculex antiquus, was found – the Burmese amber was from the mid-Cretaceous.

So, what kind of viruses might the new ancient mosquitoes have carried?

“Although 46 million years old, they look very similar to some living species of the same genus Culiseta,” Dr Harbach said. “Culiseta kishenehn bears close resemblance to the living North American Culiseta melanura, which is a vector of Eastern and Western equine encephalitis viruses (EEE and WEE).”

“These viruses quickly infect the brains of horses and cause paralysis and very often death. EEE can infect amphibians, reptiles, birds and mammals, including humans. And there is currently no cure for the human form which is sometimes fatal,” Dr Harbach said.

“There were no horses or humans during the Eocene epoch and many living species of Culiseta feed on birds. So these ancient mosquitoes probably fed on birds too,” he said. “However, mosquitoes are basically opportunistic and will feed on other types of animals if their preferred hosts are unavailable.”

“Since some of today’s mosquitoes also feed on reptiles, could the more ancient mosquitoes have sucked from a dinosaur?” Dr Harbach said: “it’s possible. Evidence suggests mosquitoes evolved in the Jurassic Period (200-146 million years ago). If the early ancestral mosquitoes had already evolved to feed on blood, it is conceivable that they may have fed on dinosaurs.”

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