Thomas Scott and his researchers are using GPS, or global positioning system, to pinpoint people’s movements in Iquitos, Peru.

“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 at UC Davis. The scientists also interview people who have dengue to try to determine where they were bitten by an infected mosquito. Tracking the general public and those infected enables the researchers to identify high-risk locations and direct preventive measures at those places to save lives.

His team’s work is aimed at preventing dengue infection in Peru but also has ramifications elsewhere, including California.  “We expect that results from our study will be useful for protecting people from other infectious disease like the flu, measles, etc. that are often contracted from other people in places where people congregate,” Scott said.

Dengue, transmitted by Aedes egypti, or the yellow-fever mosquito, is 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 are some 3.6 million people, primarily in tropical and sub-tropical countries around the world.

The Centers for Disease Control Prevention estimates the annual cases of debilitating dengue fever at 50 million to 100 million. The most severe form of the disease, dengue hemorrhagic fever (DHF), strikes half a million people a year. 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.

“We don’t have endemically transmitted dengue in California today, but we may have it in the future,” Scott said. The mosquito vector of dengue is now found in Arizona and public health officials are “very worried” about possible outbreaks in California, Scott said. People traveling from dengue-endemic countries, including Peru and Mexico, could bring the disease into the United States.

“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.

He set up the field station in Iquitos 10 years ago and also maintains stations in Mexico and Thailand.

“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.”

After identifying dengue hot spots, they can design strategies that most effectively deliver pesticides to those locations to kill virus-infected mosquitoes and prevent 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 said the four different dengue serotypes pose disease-prevention challenges.

“If you create a vaccine for DEN-1, it won’t be effective for DEN-2, DEN-3 or DEN-4,” Scott said. “A dengue vaccine will have to protect against all four viruses simultaneously.”

Iquitos, the largest city in the Peruvian rain forest, is the world’s most populous city (400,000) unreachable by road. 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.

The author of more than 150 publications on mosquito-borne diseases, 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,” he said.

Scott directs the state-funded UC Mosquito Research Laboratory, based 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 and has directed their research there since 1999; program manager Leslie Sandburg; five postdoctoral students; five graduate students; and collaborators at his field sites in Peru, Thailand and Mexico.

Scott was recently elected a 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.”

He 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.

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.

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,” Scott 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,” he said. “Programs with the ability to integrate information from diverse but relevant disciplines will lead the way in recognizing and preventing disease.”

For more information on dengue and the work of the UC Davis research team, see  http://entomology.ucdavis.edu/news/tomscottdengue.html.