Amidst concerns over the safety of DEET, scientists are on the lookout for a new mosquito repellent. Now they may have found a way to keep biting insects at bay–by blocking their olfactory sense, according to a paper published in Nature.
Mosquitoes sense the presence of humans and animals by detecting the carbon dioxide we exhale with each breath. Researchers have found two compounds, 2,3-butanedione and 1-hexanol, that could keep the biters at bay by blocking the insects’ ability to detect this gas. Using these compounds could be advantageous because the amount of chemical required is relatively small…. Further, the chemicals themselves are not complicated to manufacture and are available through conventional sources. “From both perspectives, this adds up to a viable tool in tackling the problems like that of malaria in Africa” [Scientific American], says study coauthor Anandasankar Ray. Considering the number of diseases spread by insects such as mosquitoes–for example, 250 million people contract malaria each year–there’s a lot more at stake here than a few itchy bug bites.
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Mosquitoes that have made their way to the Galapagos Islands via tourist planes and boats are threatening the rare native species endemic to the region, according to a study published in the journal Proceedings of the Royal Society B.
Culex quinquefasciatus, known as the southern house mosquito, can carry diseases dangerous to wildlife, such as avian pox and West Nile virus. Not only have the insects hopped a ride onto the islands, but they’ve also bred with native species once they reach the shore, the study found. That means they pose an ongoing threat to the Galapagos’ rare species and delicate ecosystem, which inspired Darwin’s theory of evolution after he observed the island’s unique array of wildlife. “You only need a single infectious mosquito to initiate a disease cycle,” [co-author Simon] Goodman…[T]he Galapagos “have globally important biodiversity — endemic species found nowhere else in the world,” said Goodman [Telegraph].
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Powerful bug repellant DEET may do more than keep mosquitoes and other biting critters at bay–it might cause neurological damage in mammals, according to a study published in BioMed Central Biology.
Developed in 1946 by the U.S. Army, DEET has been used by the public for more than half a century to repel bugs like mosquitoes, along with the diseases they can carry. The new study, however, shows that DEET—aka N,N-diethyl-meta-toluamide—may be harmful for a variety of animal cells. In lab tests, it caused damage to mosquitoes, cockroach nerves, mouse muscles, and enzymes purified from fruit flies and humans. Applications of DEET slowed or halted the actions of the enzyme acetylcholinesterase. This enzyme hangs out between nerve and muscle cells, breaking down a messenger molecule after it has passed information from one cell to another. If this messenger isn’t properly recycled, it can build up and lead to paralysis [Science News].
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The mighty tortoises that roam the Galapagos Islands may not have many predators, but a new study suggests that the giant reptiles could run into serious problems due to the diminutive black salt marsh mosquito. Researchers genetically analyzed the mosquito, and found that it was not introduced recently by humans but instead arrived about 200,000 years ago. Since then the insect has evolved so much it is practically a distinct species from the mainland variety. For one thing, the insect has adapted to be able to feast on the blood of lizards, tortoises and other reptiles and not solely on mammals, as it does on the mainland [The New York Times].
That diversity of diet is what has researchers worried. If the black salt marsh mosquito picks up a disease like avian malaria or West Nile fever, it could quickly spread the disease to the Galapagos’s rare tortoises and marine iguanas. Says study coauthor Andrew Cunningham: “With tourism growing so rapidly the chance of a disease-carrying mosquito hitching a ride from the mainland on a plane is also increasing, since the number of flights grows in line with visitor numbers…. If a new disease arrives via this route, the fear is that Galapagos’ own mosquitoes would pick it up and spread it throughout the archipelago” [Telegraph].
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The U.S. Food and Drug Administration has approved human trials of a new malaria vaccine: it is made from a weakened form of the entire malaria-causing parasite, Plasmodium falciparum, extracted from irradiated mosquito spit. Sanaria, the company producing the vaccine, has been working with a particular stage of the P. falciparum parasite called a sporozoite. This is the stage when it leaves the mosquito’s salivary glands to enter the human bloodstream [Reuters].
To produce the vaccine, Sanaria weakens the parasite by feeding human, infected blood to mosquitoes, then [exposes] the mosquitoes to enough irradiation to cripple the parasite [New Scientist]. The mosquitoes are then killed and their saliva is extracted by hand, with each of six laboratory workers averaging a rate of 100 mosquitoes per hour. With every mosquito containing about two doses in its spit, Sanaria founder Stephen Hoffman estimates that about 1,200 doses are produced per hour.
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A mosquito’s whiny buzz may be one of the most annoying noises to human ears, but for some mosquitoes it’s an intricate love song. A new study of the mosquito Aedes aegypti, which carries the infectious diseases dengue fever and yellow fever, has shown that when males and females mate they adjust the speed of their beating wings until their two buzzes combine to produce a harmonious tone. And this isn’t just gee-whiz science: Researchers say the finding could help in the fight against the disease-carrying insects.
The male mosquito’s buzz, or flight tone, is normally about 600 cycles per second, or 600-Hz. The female’s tone is about 400-Hz. In music, he’s roughly a D, and she’s about a G. So the male brings his tone into phase with the female’s to create a near-perfect duet. Together, the two tones create what musicians call an overtone — a third, fainter tone at 1200-Hz. Only then will the mosquitoes mate [NPR]. Researchers were surprised that the mosquitoes could detect the overtone, because they previously believed that A. aegypi males couldn’t hear frequencies above 800-Hz, and the females were thought to be completely deaf.
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To combat the persistent scourge of dengue fever, researchers have infected the virus-carrying mosquitoes with a bacterium that kills them before they’re old enough to transmit the virus to humans. Researchers say this “biopesticide” technique could cheaply and quickly reduce deaths due to dengue fever in the tropics, as the bacterium could rapidly spread through mosquito populations. Traditional [malaria-oriented] methods for controlling the spread of mosquito-borne disease, such as using bed nets and draining wetlands, are ineffective for the Aedes aegytpi mosquitoes that spread dengue fever virus because they bite during the day and thrive in urban areas [Nature News].
While the new process has only been tested in the lab thus far, researchers are very optimistic about the possibility of whittling away at the 20,000 deaths caused each year by the disease, and say it’s conceivable that transmission of the virus could be reduced to nearly zero. “We’re not trying to eliminate the population, but to let a bacterial symbiont in, and then shift the population,” said University of Queensland bacterial geneticist Scott O’Neill. “There will still be mosquitoes around, but only young ones. It’s a biological control” [Wired News].
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Firing new shots in the malaria war, a vaccine still in the testing stage is now a step closer to becoming a public health reality [Science News]. Two field trials in Kenya and Tanzania showed that the experimental drug reduced malaria infections by more than 50 percent in infants and young children; if a final set of trials proves that the vaccine is indeed safe and effective, the vaccine could be ready for use by 2011.
If the phase three trials are successful, it would be “an extraordinary scientific triumph,” said Dr. W. Ripley Ballou, deputy director for vaccines and infectious diseases for the Bill and Melinda Gates Foundation, which helped fund the research. But more importantly,” Ballou added, “it could save millions of children’s lives” [Los Angeles Times]. Malaria kills about 1 million people around the world each year, and most of the victims are children under the age of five.
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Researchers have decoded the genomes of two different malaria parasites that plague people in Southeast Asia and South America, and say the new information will boost efforts to find a vaccine for the mosquito-borne disease. The work builds on the sequencing of the first malaria genome six years ago, when scientists tackled the most deadly malaria parasite, Plasmodium falciparum, which is endemic in Africa. By comparing the genetics of Plasmodium falciparum to that of the newly sequenced species, P. knowlesi and P. vivax, the two teams have begun to identify the different mechanisms by which each species maximizes its chances of evading the host immune system [The Scientist].
P. vivax is the main cause of malaria in Latin America and Southeast Asia, and although it’s rarely deadly researchers say it still causes plenty of misery. It’s also challenging to eradicate because it can lie dormant in the liver for months. “It makes people very sick,” says lead researcher Jane Carlton…. “It can come out of the liver weeks or months after the initial mosquito bite. That makes it a very serious risk to human health.” Vivax malaria is so debilitating that sufferers, most of whom are poor, can’t support themselves or their families. “Vivax is one of the stealth reasons that poor people can’t escape poverty,” says [tropical disease expert] Peter Hotez [USA Today].
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A warmer world will also be a sicklier place for both animals and humans, according to a new report from the Wildlife Conservation Society (WCS). Dubbed the “deadly dozen,” sicknesses such as Lyme disease, yellow fever, plague, and avian influenza, or bird flu, may skyrocket as global shifts in temperature and precipitation transform ecosystems. Babesia, cholera, Ebola, intestinal and external parasites, red tides, Rift Valley fever, sleeping sickness and tuberculosis round out the list [National Geographic News].
The report spells out how global warming is changing the ranges and habitats of animals that carry these infectious diseases, bringing the ticks that transmit Lyme disease and the mosquitoes that carry yellow fever and Rift Valley fever into contact with new human populations. “We’ve seen Lyme disease work its way up from the US into Canada, and West Nile fever as well,” said William Karesh, director of WCS’s global health programmes. “Basically what you have now are fewer frozen nights in this region, and that allows the ticks and mosquitoes that carry these diseases to survive further north” [BBC News].
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Finally, the U.S. Department of Defense is working on a bomb that even peaceniks can get behind — a bug bomb!
Motivated by the need to protect soldiers in the field from biting pests, the Defense Department teamed up with the Department of Agriculture to search for a longer-lasting and more effective insect repellent. “That was the principal motivation, the usability for the military,” says USDA investigator Ulrich Bernier. “You don’t want your soldiers reapplying every 15 to 20 minutes” [Science News].
Researchers have already identified several chemical compounds that seem far more effective than the current standard-bearer, DEET. In one test, a cloth soaked with a particularly promising compound repelled mosquitoes for 73 days, while DEET-soaked cloth lasted only 13 days.
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