DAVIS -- Thomas Scott knows his foe well -- a day-biting mosquito that prefers to feed on human blood.

When the 6-foot-6 medical entomologist leaves his mosquito research laboratory at the University of California, Davis, he’s likely heading for his field stations in Peru, Thailand or Mexico to try to stop a tiger-striped mosquito from transmitting dengue, the world’s worst insect-transmitted virus.
Scott’s goal: to save lives through research, surveillance and implementation of disease prevention strategies.

“I study the patterns of human infection with dengue virus, doing detailed studies of mosquito populations and disease in humans in order to predict which prevention strategies work the best,” said Scott, who assesses risks, develops computer models and implements disease prevention strategies.

The culprit: Aedes egypti, or the yellow-fever mosquito, that transmits dengue virus to people.

The disease: Dengue, caused by any one of four serotypes or closely related viruses known as DEN-1, DEN-2, DEN-3, or DEN-4. Nicknamed “break bone fever,” classic dengue is characterized by high fever, headaches, muscle and joint pain, nausea, vomiting and a rash.

At risk: Some 3.6 million people, primarily in tropical and sub-tropical countries around the world.

The prevalence: Some 50 to 100 million annual cases of debilitating dengue fever. The most severe form of the disease, dengue haemorrhagic fever (DHF), strikes half a million a year, according to the Centers for Disease Control and Prevention. An estimated 5 percent with DHF die.

There’s no vaccine. There’s no cure. The only way to prevent this disease is to kill the mosquito vector.

“What’s challenging is that there are four different dengue serotypes and each one can cause dengue fever,” said Scott, a noted mosquito-borne disease expert and newly elected fellow of the prestigious American Association for the Advancement of Science (AAAS) for "distinguished contributions to the biology and ecology of mosquitoes and his leadership in developing strategic concepts for preventing dengue fever and other mosquito-borne diseases.”

“If you create a vaccine for DEN-1, it won’t be effective for DEN-2, DEN-3 or DEN-4,” said Scott, who was infected with DEN-2 in Iquitos, Peru sometime prior to 2003 but did not get sick. Fellow researcher Amy Morrison contracted DEN-3 in 2003 in Iquitos and did become ill. “A dengue vaccine will have to protect against all four viruses simultaneously,” Scott said.

Iquitos, the largest city in the Peruvian rain forest, is the world’s most populous city (400,000) unreachable by road. Travelers arrive by plane or boat. Founded in the 1750s and located along the Amazon River in northeastern Peru, near Columbia and Brazil, the port city bustled during the rubber boom. Now Iquitos is known for its lumber shipments.

And dengue.

Dengue is endemic in Iquitos, in that it occurs continuously and with predictable regularity.

Scott and his researcher colleagues are using a new tool, global positioning system (GPS), to track people’s movements to determine where they go during their daily activities and where they are at greatest risk of contracting dengue from the bite of an infected mosquito.

We track residents wherever they travel in the community: to their home, to homes of friends and relatives, to the market, and to church,” said Scott, a professor of entomology and former vice chair of the Department of Entomology. The tracking enables the researchers to identify high risk locations and direct preventive measures at those places to save lives.

“The people of Iquitos are poor but very social and mobile,” Scott said. “It’s a challenge to track their movements. A child may move from living at home to spending several months at his grandmother’s house before returning home again. By following where they go, seeing how much time they spend there, and how often they are bitten by mosquitoes at each site we can determine which locations represent the greatest risk for infection.”

Like CSI, Scott’s team uses DNA fingerprinting to determine the exact person a mosquito full of blood bit. After identifying dengue hot spots, they can design strategies that most effectively delivery pesticides to those locations to kill virus infected mosquitoes and prevent disease.

The rule of 20-80 often applies: 20 percent of the people are responsible for 80 percent of the transmission of the disease. “Directing control to hot spots,” Scott said, “can be a more effective use of limited public health resources than trying to cover the entire city.”

Scott’s work has not gone unnoticed. “Tom is a pioneer in using longitudinal, field-based studies to generate unprecedented detailed data that test and refine assumptions about a mosquito’s role in the transmission of viral pathogens,” said UC Davis entomology professor James Carey, who co-nominated Scott for AAAS award.

“He is a leader in the integration of ecologic and population biology concepts into genetic strategies for prevention of mosquito-borne disease,” Carey said. “In his international programs Scott is generating the missing, difficult to obtain, detailed data that are essential for assessing current recommendations to prevent mosquito-borne viral disease, rigorously test fundamental assumptions in public health policy, and develop innovative, cost and operationally effective strategies to prevent some of the most important infectious diseases of humans.”

Said co-nominator Robert Page Jr., professor and founding director of the School of Life Sciences at Arizona State University and former chair of the UC Davis Department of Entomology: “Tom Scott is a world leader in the ecology and epidemiology of tropical arthropod borne-diseases. His election as a fellow of the Association for the Advancement of Science is in recognition of his contributions to the field of medical entomology both as a researcher and as a leader in his discipline. The award is well deserved and overdue.”

Medical entomologist Anthony James of UC Irvine said Scott is an internationally recognized scientist who conducts groundbreaking studies to determine threshold dynamics (density and absolute numbers of infected mosquitoes). Scott has published more than 150 papers in scientific journals.

Tom Scott discovered that Aedes aegypti gains a reproductive and survival advantage from feeding frequently and preferentially on human blood versus the blood of other animals. “Because it bites people so often and transmits all four dengue serotypes, this mosquito is a very good vector of dengue and presents a formidable challenge to public health officials,” Scott said.

“I started out in basic sciences,” Scott said, “and for the last 10 years have shifted my attention to prevention of vector-borne disease.” A native of New Jersey, Scott received his bachelor of science degree in business and his master’s degree in biology from Bowling Green (Ohio) State University before obtaining his doctorate in ecology from Pennsylvania State University. He completed his post-doctoral research in epidemiology at Yale University.

Overall, the UC Davis medical entomologist takes a multidisciplinary approach to the investigation of the ecology, epidemiology and control of mosquitoes that cause disease, with a focus on dengue; malaria, transmitted by Anopheles mosquitoes; and West Nile virus, transmitted primarily by Culex mosquitoes.

Scott directs the state-funded UC Mosquito Research Laboratory, based in Briggs Hall on the UC Davis campus. His team includes Anthony “Anton” Cornel, associate professor of entomology based at the Kearney Agricultural Center, Parlier; researcher Amy Morrison who lives in Iquitos, Peru and has directed their research there since 1999; program manager Leslie Sandburg; five postdoctoral students; five graduate students; and a long list of collaborators at his field sites.

Scott serves as the principal investigator or key collaborator on seven research projects. Some are funded by the National Institutes of Health, the Bill and Melinda Gates Foundation and the World Health Organization. Since 1984, funding of his work has totaled more than $86 million, with $16.7 million going directly to his lab.

In addition to his 10 years in Iquitos, Scott has studied dengue in Thailand for 20 years, and in Tapachula, Mexico for three years.

His work in Mexico, which is funded by a grant from the Bill and Melinda Gates Foundation program on Grand Challenges in Global Health, involves genetic modification of mosquitoes. The premise: Modify the genetics of mosquitoes to either reduce their population densities or render them incompetent to transfer diseases.

Scott also participates in the Innovative Vector Control Consortium: a large grant from the Bill and Melinda Gates Foundation to support pesticide development partnerships and develop novel malaria and dengue intervention strategies in Peru, Mexico, South Africa, Mozambique and Zambia.

More locally, he works closely with the Sacramento-Yolo Mosquito Vector Control District to combat transmission of West Nile virus by Culex mosquitoes.

Earlier this year Scott hosted the 42nd annual U.S.-Japan Parasitic Disease Conference on the UC Davis campus. Some 100 scientists from throughout the world participated in the Jan. 16-18 conference “to develop a cross-cutting perspective on what the priorities should be for the future research on arthropod vectors of disease,” he said.

Scott, one of six U.S. scientists and five Japanese scientists serving on the U.S.-Japan Parasitic Diseases Panel, says that it is unlikely that vector-borne diseases will be eliminated in the near future.

With new and emerging diseases, increasing national and international travel, settlement in endemic areas, and the proliferation of commerce, we can expect disease from vector-borne pathogens to increase, he said.

“Well-designed and innovative strategies for disease control will be based on the application of new scientific knowledge, availability of sustainable resources, and continued political support,” Scott said. “Programs with the ability to integrate information from diverse but relevant disciplines will lead the way in recognizing and preventing disease.”

Meanwhile, his lab will continue to use “a multidisciplinary approach for addressing important questions regarding the ecology, evolution, epidemiology, and disease risk assessment of arthropod-borne viral diseases based on a detailed understanding of vectors, viruses, and their human hosts.”

Web site link: http://entomology.ucdavis.edu/news/tomscottdengue.html