The PLOS ONE journal published “Effects of Fluctuating Daily Temperatures at Critical Thermal Extremes on Aedes aegypti Life-History Traits," written by lead author Lauren Carrington and four other scientists from Thomas Scott’s Mosquito Research Laboratory and the Center for Vectorborne Diseases (CVEC).
Their work analyzed how natural temperature fluctuations affect the population growth rate of the dengue mosquito. Basically, temperature effects on larval development time, larval survival and adult reproduction depend on the combination of mean temperature and the magnitude of fluctuations.
“The effect of temperature on insect biology is well understood under constant temperature conditions, but less so under more natural, fluctuation conditions,” said Carrington, who completed her three-year postdoctoral fellowship last December in the Scott lab and continues research projects with the lab. She is now based at the Nossal Institute for Global Health, University of Melbourne, Australia.
The research is expected to lead to greater accuracy of applications for mosquito surveillance and disease prevention.
“An improved understanding of mosquito responses to natural temperature variation,” Carrington said, “will enhance the effectiveness of vector control strategies, thereby reducing transmission of mosquito-borne diseases, such as dengue fever.” By using constant temperatures, scientists can under- or -over estimate values, she said.
“In the field, mosquitoes, and other insects, are exposed to a constantly changing environment, with fluctuations in temperature throughout the day, every day. In the lab, however, experimental protocols generally try to minimize as much variability as possible, and temperature is often the first element to be standardized.”
Co-authors are Veronica Armijos, Christopher Barker, Louis Lambrechts and Thomas Scott.
Dengue is spread by an infected female Aedes aegypti mosquito, 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 and the most severe form of disease is life-threatening dengue hemorrhagic fever or DHF.
Some 500,000 people with severe dengue are hospitalized each year, according to the World Health Organization (WHO), and about 2.5 percent of those affected die.
“Dengue takes an enormous toll on human health worldwide, with as many as 4 billion people at risk—half of the world’s population--and 400 million new infections each year,” said Scott, a professor of entomology at UC Davis and active in CVEC.
In an article published this week in the Proceedings of the National Academy of Sciences (PNAS), the UC Davis medical entomologists and their colleagues found that human movement—people going from house-to-house to visit their friends and relatives—is a key component to driving the virus transmission. (Read PNAS paper)
The research site is Iquitos, nestled in the heart of the Amazon rain forest of northeastern Peru. It's considered one of the world’s primary “open laboratories” to study the transmission of the virus.
The Aedes aegypti mosquito is a day-biting mosquito and we humans are its favorite host/target.
The ground-breaking research shows why it's crucial to focus on people movement, not just on the traditional mosquito control-and-prevention methods, such as applying insecticides and eliminating water-filled containers that can provide a larval habitat.
As lead author/medical entomologist Steve Stoddard said: "This finding has important implications for dengue prevention, challenging the appropriateness of current approaches to vector control."
“Interestingly, it didn’t matter how far away the visited houses were," Stoddard said. "The mosquito that transmits dengue virus prefers to stay in small areas, say in less than a 100-meter radius, but the distance between houses was often much greater than this. So it only makes sense that humans are frequently spreading the virus around as they commute between their homes and the homes of their friends and family. Altogether the data demonstrate what we expected, that human movements are really key to the transmission of this mosquito-borne virus.”
Said Scott, professor of entomology at UC Davis and director of the Mosquito Research Laboratory: “Dengue takes an enormous toll on human health worldwide, with as many as 4 billion people at risk—half of the world’s population--and 400 million new infections each year. The results from our study are focusing attention to the role human social networks in virus invasion and epidemic spread.
"At our Peru study area, we found that infection risk is based on the places a person visits and transmission dynamics are driven by overlapping movements of people who recently visited the same places, like the homes of their family and friends.”
Bottom line: The scientists found that people movement not only defined individual infection risk and local patterns of incidence, but resulted in the rapid spread of the virus and marked heterogeneity in transmission rates.
Next phase of the research? It's aimed at "understanding how variation in human behavior influences transmission and applying that knowledge in enhanced disease prevention strategies,” said Scott, the principal investigator of a National Institutes of Health (NIH)-funded grant.
With some 4 billion people worldwide at risk, and with 400,000 million new infections each year, dengue is indeed taking its toll. Every year some 500,000 people with severe dengue are hospitalized, and 2.5 percent die.
So are researchers from the Thomas Scott lab at UC Davis.
Scott, a medical entomologist who directs the state-funded UC Mosquito Research Laboratory, and his field director Amy Morrison, based in Iquitos, Peru, know their foe well.
Their goal: to save lives through research, surveillance and implementation of disease prevention strategies.
Morrison talked about the research efforts today on National Public Radio (NPR).
Morrison told Charles: ""What's fascinating to me about aegypti is it's probably the mosquito that's most closely associated with human beings, and the most adapted to human beings."
The tiger-striped mosquito, is a daybiting mosquito that prefers human blood. Some 2.5 to 3 billion people, primarily in tropical and sub-tropical countries around the world, are at risk for dengue, which Scott describes as "the world's worst insect-transmitted disease." See feature on him on the UC Davis Department of Entomology website, with links to significant research work.
Aedes aegypti is out for blood. And so are the UC Davis-based researchers tracking it.
The size and pattern of fluctuations in daily temperature have a large effect on pathogens transmitted by mosquitoes, according to groundbreaking research published today in the Proceedings of the National Academy of Sciences.
The research, led by French, Thailand and U.S. scientists and conceived by medical entomologist Thomas Scott (right) of the UC Davis Department of Entomology, targets the transmission of spread of dengue.
Dengue, transmitted by the daybiting Aedes aegypti mosquito, globally infects 50 to 100 million people yearly. At risk are some 2.5 to 3 billion people, primarily in tropical and sub-tropical countries. The most severe form of the disease, dengue haemorrhagic fever (DHF), strikes half a million a year and kills an estimated 5 percent, according to the Centers for Disease Control and Prevention.
Scott said the study helps to explain a long-standing enigma: “What are the underlying causes of seasonal fluctuations in dengue incidence?” Experiments showed that mosquitoes die faster and are less susceptible to virus infection under large temperature swings, which is typical of the low dengue season, than under moderate temperature variation, which is typical of the high dengue season.
Scott, a noted dengue expert whose goal is to save lives through research, surveillance and implementation of disease prevention strategies, has a longstanding interest in the factors that drive seasonal and annual fluctuations in diseases caused by mosquito-transmitted pathogens. “Traditional explanations for the seasonal increase in dengue are not consistent with my experience in Thailand, Peru, and Puerto Rico,” Scott said.
Three University of California entomology professors were among the 10 newly elected Fellows of the Entomological Society of America (ESA) honored at the organization's 58th annual meeting, held Dec. 12-15 in San Diego.
Their selection speaks highly of the caliber of UC professors. No more than 10 Fellows are selected for the honor every year from the 6000-member organization, and this year the UC system has three.
They are Bruce Hammock and Thomas Scott of UC Davis and Thomas A. Miller of UC Riverside.
Hammock, a distinguished professor of entomology, studies "inhibitors of epoxide hydrolases as drugs to treat diabetes, inflammation, ischemia and cardiovascular disease," the ESA statement of his work reads. "Compounds from the UC Davis laboratory are in human trials."
That in itself--from bench to bedside--is unique in the annals of entomology.
Hammock, a member of the UC Davis Medical Center's Cancer Center and the National Academy of Sciences, is not only a distinguished professor but a highly sought-after mentor who draws students to his lab from all over the world.
Scott, who directs the UC Mosquito Research Laboratory at Davis, is one of the key "go-to" researchers studying dengue. When he's not in his UC Davis lab, you can usually find him doing research in Peru, Thailand or Mexico. Scott is especially known for his research on mosquito ecology, evolution of mosquito virus interactions, epidemiology of mosquito-borne disease, and evaluation of novel products and strategies for mosquito control and disease prevention.
Scott is a fellow of the American Association for the Advancement of Science and is a past president of the Society for Vector Ecology. He serves as a subject editor for the American Journal of Tropical Medicine and Hygiene. (More on Hammock and Scott on the UC Davis Department of Entomology website.)
ESA officials pointed out that Miller's research "has included structure and function of the insect circulatory system; mode of action of insecticides; insect neuromuscular physiology; physiology, toxicology and behavior of pink bollworm in cotton fields; transgenic insects; and applied symbiosis for crop protection and biopesticides for crop protection. "
Miller's university teaching includes insect physiology, insect toxicology and first year biology. Current projects include control of bush cricket pests of oil palm trees in Papua New Guinea, oversight of field trials of transgenic grapevines with resistance to Pierce's disease, biotechnology for control of desert locust, and regulatory control of insect transgenic technologies.
In 2003 Miller was awarded the Gregor J. Mendel Medal for Research in Biological Sciences by the Czech Academy of Sciences. That's just one of his many honors.
Indeed, the list of honors and accomplishments for these three UC entomologists could easily fill a book!