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Global Burden of Dengue
The mosquito-borne viral disease known as “breakbone fever,” is three times more prevalent than originally thought, according to a research paper published today in Nature and co-authored by dengue expert Thomas Scott of UC Davis.
In their research paper, titled “The Global Distribution and Burden of Dengue,” Scott and the 17 other team members estimated that 350 million people are infected each year--more than triple the World Health Organization’s current estimate of 50 to 100 million.
Professor Simon Hay of the University of Oxford led the research as part of the International Research Consortium on Dengue Risk Assessment, Management and Surveillance.
“Dengue takes an enormous toll on human health worldwide, with as many as 4 billion people at risk," said Scott, a UC Davis professor of entomology and worldwide expert on the epidemiology and prevention of dengue. He chairs the mosquito-borne disease modelling group in the Research and Policy for Infectious Disease Dynamics (RAPIDD) program of the Science and Technology Directory, Department of Homeland Security, Fogarty International Center, National Institutes of Health.
“The results of our study and infrastructure that created the dengue maps fill a critical gap in the battle against dengue,” said Scott, who maintains field research programs in Iquitos, Peru, and Khamphaeng Phet, Thailand. “Prior to this, without rigorously derived dengue estimates that can be continuously updated, it was not possible to know with confidence where and when to direct interventions for greatest potential impact or to objectively assess the effectiveness of regional and global control efforts. That kind of knowledge was among the most important missing information for developing enhanced dengue prevention programs.”
The highly infectious tropical and subtropical disease is spread by the bite of an infected female Aedes aegypti, a day-biting, limited flight-range mosquito that prefers human blood to develop its eggs. Dengue is caused by four distinct, but closely related, viruses. The most severe form of disease is life-threatening dengue hemorrhagic fever or DHF.
The researchers assembled known records of dengue occurrence worldwide and used a formal modelling framework to map the global distribution of dengue risk. They then paired the resulting risk map with detailed longitudinal information from dengue cohort studies and population surfaces to infer the public health burden of dengue in 2010.
“There are currently no licensed vaccines or specific therapeutics, and substantial vector control efforts have not stopped its rapid emergence and global spread,” the researchers wrote.
Dengue has now begun to appear along the southern border of the United States, including Texas. Florida has also reported cases of dengue.
Of the 96 million clinically apparent dengue infections, Asia bears 70 percent of the burden, the research paper revealed. India alone accounts for around one-third of all infections.
Professor Thomas Scott, a worldwide expert on dengue, is pictured in Kenya.
Global dengue risk. Areas in red indicate high risk for dengue occurrence while green areas indicate low risk. (Map courtesy of Jane Messina)
Natives vs. Non-Natives
That they're Public Enemy No. 1?
According to a recent Nature journal essay, non-natives are so vilified today that a “pervasive bias” exists against non-native species, a bias embraced by “the public, conservationists, and managers and policy-makers, as well by as many scientists, throughout the world.”
The native-vs.-non-native species distinction appears to be the “guiding principle” in today’s conservation and restoration management, say 19 ecologists in their essay, “Don’t Judge Species on Their Origins.”
Mark Davis, a biology professor at Macalester College, St. Paul, Minn., is the lead author. The other co-authors include Scott Carroll of UC Davis.
Carroll, an ecologist in professor Sharon Lawler’s lab, and the founding director of the Davis-based Institute for Contemporary Evolution, contributed his work on conciliation biology to the thought-provoking essay. He holds a doctorate in biology from the University of Utah.
“Global change alters conditions for all species, and from a practical perspective, origin can be only one of many criteria we consider,” Carroll told us. “Appraising non-native organisms more openly invites us to more seriously contemplate our aims when managing novel communities of mixed origin.”
Carroll is often out chasing soapberry bugs (a key research interest), writing research papers and delivering presentations. He considers soapberry bugs "wondrous examples of evolution happening right now--as we change the world, these beautiful insects are quickly adapting, and in the process directly revealing how evolution works."
You can't miss his presence. At 6 foot-10 inches, he towers over his colleagues.
And the soapberry bugs!
Related Links:
Department of Entomology website
Conciliation Biology: the Eco-Evolutionary Management of Permanently Invaded Biotic Systems by Scott Carroll, published in 2011 in Evolutionary Applications.
Soapberry Bugs of the World Website (Scott Carroll)
Scott Carroll Website
Scott Carroll: Curriculum Vitae
Soapberry bug on the UC Davis campus. (Photo by Kathy Keatley Garvey)
'The Treacherous Scent of a Human'
It's a killer, pure and simple.
But the issue is as complex as it comes.
The malaria mosquito, from the genus Anopheles, infects some 350 to 500 million people a year, killing more than a million. Most are young children in sub-Saharan Africa.
Female mosquitoes “bite” because they require a blood meal to develop their eggs. They detect their prey via olfactory receptor neurons found on their antennae, the insect equivalent to the human “nose.”
When Anopheline mosquitoes are infected with a parasite that causes malaria, the insect-host transmission occurs. The result: a deadly killer.
Identifying exactly how malaria mosquitoes detect their human prey is crucial to developing strategies for mosquito control, says chemical ecologist Walter Leal, professor of entomology at the University of California, Davis.
Leal, recently asked to write a "News-and-Views" piece on a Yale-Vanderbilt study for the international science journal, Nature, did so eloquently in its March 4th edition. He praised the scientific report as a “milestone discovery in our understanding of the malaria mosquito’s sense of smell.”
In the article, headlined "The Treacherous Scent of a Human," Leal zeroes in the widespread threat of malaria, a disease that threatens half of the world’s population. It's "an accessory to the deaths of about one million humans every year,” Leal wrote. “Globally, the number of people who get malaria each year is greater than the population of the United States.”That's putting a number on the numbers.
The Yale-Vanderbilt team, headed by John Carlson of the Yale Department of Molecular, Cellular and Developmental Biology, examined 79 of the malaria mosquito’s odorant receptors, finding that some are well-tuned to detect specific human odors and others aren’t. Certain odorants activate some receptors but inhibit others, according to their comprehensive study published March 4 in Nature.
Indeed. The Leal lab back in 2008 published groundbreaking research that revealed the secret mode of the insect repellent, DEET. The scent doesn't jam the insect senses and it doesn't mask the smell of the host, as scientists previously thought. Mosquitoes avoid it because it smells bad to them.
Leal advocates more molecular studies in the war against malaria and other mosquito-borne diseases. But that research can't stand alone. As he succinctly points out: “The development of effective malaria control will require a multidisciplinary approach that includes, but is not limited to, improvements to social infrastructure in countries affected by disease, vaccination programs and vector management.”
New mosquito attractants or repellents, he says, could be developed through reverse chemical ecology, determining which odorant attracts and which repels.Mosquitoes don't like the scent of DEET. What else do they NOT like?
The study, as Leal correctly observes, "offers a fresh strategy for controlling the unwitting accessories to one of the world’s most prolific killers.”
Walter Leal in lab
Killer
