- Author: Kathy Keatley Garvey
The study, published in the Public Library of Science (PLOS), Neglected Tropical Diseases, contradicts the long-held assumption that once you're infected with a particular dengue serotype, you won't get it again.
“Our most significant result from this study is that immunity to dengue viruses does not always provide perfect protection from reinfection,” said principal investigator and medical entomologist Thomas Scott, distinguished professor and now emeritus, UC Davis Department of Entomology and Nematology. “The public health implications include evaluation of dengue vaccines, interpretation of a person's virus exposure history and susceptibility to new infections, and design of dengue surveillance programs.”
Dengue infects 400 million people worldwide each year, and 4 billion people or nearly half of the world's population are at risk for dengue,” said Scott, who has studied dengue more than 25 years and is recognized as a leading expert in the ecology and epidemiology of the disease. “There is no vaccine nor drug that is effective against this virus.”
“This finding could help explain results of dengue vaccine trials that showed poor efficacy against one of the four serotype,” Stoddard said. “It also has broad implications for vaccine development.”
The research team investigated the "validity of the fundamental assumption" by analyzing a large epidemic caused by a new strain of DENV-2 that invaded Iquitos, Peru, in 2010-2011, 15 years after the first outbreak of DENV-2 in the region.
"Our data indicates that protection from homologous DENV re-infection may be incomplete in some circumstances, which provides context for the limited vaccine efficacy against DENV-2 in recent trials," the research team wrote. "Further studies are warranted to confirm this phenomenon and to evaluate the potential role of incomplete homologous protection in DENV transmission dynamics."
Scott and Amy Morrison of the Scott lab and U.S. Naval Medical Research Unit, co-directed the project in Iquitos. The paper is also the work of Sandra Olkowski and Kanya Long of the Scott lab; Robert Reiner of Andrews University, Berrien Springs, Mich., and the Fogarty International Center; Brett Forshey, Angelica Espinoza, Stalin Vilcarromero, Tadeusz J. Kochel and Eric Halsey of the U.S. Naval Medical Research Unit; Helen Wearing, University of New Mexico, Alburquerque; and Wilma Casanova, Universidad Nacional de la Amazonía Peruana, Iquitos, Perú.
While vaccines are under development, it is not clear how they can be best applied when they are available, including in combination with other interventions like mosquito control, Scott said. “New disease prevention tools, in addition to vaccines, and an improved understanding of virus transmission dynamics, which will enhance surveillance and epidemic response, are needed to reduce the global burden of dengue.”
The paper, “Incomplete Protection against Dengue Virus Type 2 Re-infection in Peru,”
is online at
http://journals.plos.org/plosntds/article?id=10.1371/journal.pntd.0004398
Related Links:
- Author: Kathy Keatley Garvey
They were honored at a recent meeting of ASTMH in New Orleans for their sustained professional excellence in their field. Fellows are selected for their work in "any phase of tropical medicine, hygiene, global health and related disciplines," ASTMH officials said.
Scott, internationally known for his work with on the ecology and epidemiology of dengue, focuses his work on contributing to improved public health in the United States and in the developing world, where resources are inadequate and help is desperately needed. His expertise centers on mosquito-transmitted disease; the bulk of his work is on dengue.
Scott received his doctorate in ecology from Pennsylvania State University, and worked as an epidemiology post-doctoral scholar at the Yale School of Medicine.
ASTMH, founded in 1903, is a worldwide organization of scientists, clinicians and program professionals whose mission is to promote global health through the prevention and control of infectious and other diseases that disproportionately afflict the global poor. Research, health care and education are the central activities of ASTMH members, whose work bridges basic laboratory research to international field work and clinics to countrywide programs.
Specific ASTMH goals include:
- Improving the health of people worldwide
- Advancing research in tropical diseases
- Fostering international scientific collaboration
- Supporting career development in tropical medicine and global health
- Educating medical professionals, policymakers and the public about tropical medicine and global health
- Promoting science-based policy regarding tropical medicine and global health
- Recognizing exceptional achievement in tropical medicine and global health
- Author: Kathy Keatley Garvey
Distinguished professors are scholars whose work has been internationally recognized and acclaimed and whose teaching is excellent. The UC Davis Department of Entomology and Nematology now has four distinguished professors: entomologists Bruce Hammock, Frank Zalom and Thomas Scott and nematologist Howard Ferris.
Scott, internationally known for his work with on the ecology and epidemiology of dengue, joined the then UC Davis Department of Entomology 18 years ago. He focuses his work on contributing to improved public health in the United States and in the developing world, where resources are inadequate and help is desperately needed.
“What began as an interest in the ecology of infectious disease--working as a graduate student for the Centers of Disease Control, receiving a doctorate in ecology from Pennsylvania State University, and serving as an epidemiology post-doc at the Yale School of Medicine--expanded into my current objective of applying innovative science to enhanced disease prevention and constructive contributions to the debate over improved public health policy,” Scott said.
His expertise centers on mosquito-transmitted disease; the bulk of his work is on dengue. Each year, 3.97 billion people in 128 countries are at risk, and an estimated 390 million people are infected with this mosquito-borne virus.
Scott teaches the high successful Medical Entomology (ENT 153) class at UC Davis. He focuses his research on epidemiology of mosquito-borne viral disease, mosquito ecology, evolution of mosquito-virus interactions, and evaluation of novel products and strategies for disease control.
“I aim to generate the detailed, difficult to obtain data that are necessary for assessing current recommendations for disease prevention, rigorously testing fundamental assumptions in public health policy, and developing innovative, cost, and operationally effective strategic concepts for prevention of mosquito-borne disease,” he said. For more than 35 years he has conducted arbovirus research, with an emphasis on dengue since 1990 in Asia (Thailand for the past 25 years) and Latin America (Puerto Rico, Mexico, and Peru for the past 23 years). He works closely with the Mosquito and Vector Control Association of California and the Thai and Peruvian Ministries of Health.
Scott directed two long-term dengue cohort studies in Peru and Thailand. “One of our key innovations,” he said, “was the development of a way to rapidly identify active human infections and study virus transmission dynamics across communities. “Our geographic cluster and contact tracing study designs are changing the way people investigate dengue epidemiology and are providing new insights into virus invasion, amplification, and epidemic transmission, all of which influence the design of improved disease prevention programs.”
A common theme in his dengue epidemiology research is the importance of heterogeneities in patterns of human infection, how variation in these kinds of factors affects trends in dengue transmission, and whether data on this topic can be captured and applied in an operationally amenable way.
“Research in Thailand showed that dengue transmission is remarkably focal, helped explain patterns of human and mosquito infection, and is consistent with targeting interventions for improved disease prevention. Complementary research in Thailand defined patterns in mosquito production and virus infection, gene-by-gene interactions during mosquito infection, the impact of mosquito infection on virus evolution, and the impact of daily temperature fluctuations on mosquito infection and transmission.”
“Results from human movement studies are the basis for designing, parameterizing, and testing quantitative network models on virus transmission dynamics, surveillance, and prevention and of interest for application to other infectious diseases.”
Scott is an elected fellow of the American Association for the Advancement of Science and the Entomological Society of America (ESA). He served as an editor for the American Journal of Tropical Medicine and Hygiene, Journal of Insect Science, and Journal of the American Mosquito Control Association; and is included in Who's Who in America.
In addition, he was a standing member of the United States–Japan Cooperative Medical Sciences Program Parasitic Diseases Panel; past president of the Society for Vector Ecology; chair of the Medical and Veterinary Entomology section of ESA; a standing member on the Program Committee for the annual meeting of the American Society of Tropical Medicine and Hygiene, and a member of the Robert E. Shope International Fellowship in Infectious Diseases Committee.
Scott is often asked to review grant proposals for a variety of funding agencies: National Institutes of Health; National Science Foundation; Institut Pasteur, France; Netherlands Foundation for Science and Global Development; Medical Research Council (UK), and Wellcome Trust.
Scott is currently serving an 8-year term on the Council of the International Congresses of Entomology. Recently, he was appointed to the Steering Committee of the newly formed Partnership for Dengue Control, a consolidation of vaccine developers, novel mosquito interventions, international health funders (Gates and Carlos Slim Foundations), and experts on dengue prevention. Scott was also singled out to lead a comprehensive assessment of current and project mosquito interventions for dengue and develop the conceptual basis for feasibility trials that combine mosquito control and vaccines for dengue prevention.
Scott works closely with the World Health Organization (WHO) in several of its mosquito-borne disease and dengue prevention programs: the Vector Control Advisory Group and the program to Estimate the Global Burden of Dengue.
- Author: Kathy Keatley Garvey
(News embargo lifts at noon Monday, May 19, 2014, Pacific Time)
Listen to Video, Robert Reiner (YouTube, Created by Professor James Carey)
DAVIS--Newly published research involving a 12-year study of dengue infections in Iquitos, Peru—an international team project led by researchers at the University of California, Davis—helps explain why interventions are frequently unsuccessful in efforts to prevent the mosquito-borne disease.
The research, headed by Professor Thomas Scott of the UC Davis Department of Entomology and Nematology, is published May 19 in Proceedings of the National Academy of Sciences (PNAS).
"Defining variation in the risk of dengue transmission has been a roadblock to understanding disease dynamics and designing more realistic and effective disease prevention programs,” said Scott, noted dengue researcher and a senior author of the paper, “Time-Varying, Serotype-Specific Force of Infection of Dengue Virus.”
“This study is an important step toward overcoming that obstacle,” Scott said. “We hope our results will help reduce the burden of this increasingly devastating disease."
“Typically, most infections go unnoticed and as such, measuring and modeling transmission intensity is problematic,” Reiner said.
Dengue virus is transmitted by Aedes aegypti, a mosquito that bites during the daytime as people move about in their daily routines.
“Our work suggests that certain serotypes can infect up to 33 percent of the susceptible population in a single year and that 79 percent of the population of Iquitos would need to be protected from any further infection to eliminate transmission. Further, our estimates form a detailed description of virus transmission dynamics that provides a basis for understanding the long-term persistence of dengue and for improving disease prevention programs.”
Reiner, who holds a doctorate in statistics from the University of Michigan, joined the Scott lab in September 2011. He has just accepted a position as assistant professor in the Department of Epidemiology and Biostatistics, Indiana University, Bloomington.
“The marked variation in transmission intensity that we detected indicates that intervention targets based on one-time estimates of the force of infection (FoI) could underestimate the level of effort needed to prevent disease,” the authors wrote in their abstract. “Our description of dengue virus transmission dynamics is unprecedented in detail, providing a basis for understanding the persistence of this rapidly emerging pathogen and improving disease prevention programs.”
“There is no vaccine nor drug that is effective against this virus,” said Scott, who has studied dengue more than 25 years and is recognized as the leading expert in the ecology and epidemiology of the disease.
While vaccines are under development, it is not clear how they can be best applied when they are available, including in combination with other interventions like mosquito control, Scott said. “New disease prevention tools, in addition to vaccines, and an improved understanding of virus transmission dynamics, which will enhance surveillance and epidemic response, are needed to reduce the global burden of dengue.”
The work was supported by the RAPPID program of the Science and Technology Directory, Department of Homeland Security, and Fogarty International Center, National Institutes of Health; Innovative Vector Control Consortium; U.S. Department of Defense Global Emerging Infections Systems Research Program Work Unit; Military Infectious Disease Research Program Work Units; Deployed Warfighter Protection Program, Department of Defense; and a Wellcome Trust.
- Author: Kathy Keatley Garvey
Reiner, a RAPIDD (Research and Policy in Infectious Disease Dynamics) postdoctoral fellow, studies with UC Davis Professor Thomas Scott, a worldwide expert on the epidemiology and prevention of dengue. Scott chairs the mosquito-borne disease modelling group in the RAPIDD program of the Science and Technology Directory, Department of Homeland Security, Fogarty International Center, National Institutes of Health.
“Dengue takes an enormous toll on human health worldwide, with as many as 4 billion people at risk," said Scott.
Reiner noted that “Mathematical models for the transmission of mosquito-borne diseases often rely on very simple assumptions about the population dynamics of the mosquito vectors. Linking transmission models to real-world data on mosquito abundance requires a method that smooths over the discontinuous mosquito abundance data to yield complete time series, simultaneously accounting for the effects of covariates that also vary in space or time.”
“Generalized additive models (GAMs) offer a flexible way to disentangle the relative roles of seasonality, inter-annual variation, control, temperature, and land cover as predictors of mosquito abundance," Reiner said in an abstract of his talk. "Case studies on the abundance of vectors of different pathogens in two different locations are considered: dengue virus and Aedes aegypti in Iquitos, Peru and West Nile virus and Rift Valley fever virus and Culex tarsalis, the Culex pipiens complex, and Aedes melanimon in California.”
“Using over 150,000 entomological surveys conducted at the household level within Iquitos, Peru as well as spatio-temporally explicit control efforts of varying intensity, we identify locations within the city that systematically over or under produce Aedes aegypti as well as quantitatively assess the impact of various levels of control. Within California, using a spatially explicit surveillance data set (2003-2009, 102,188 trap-nights of 4,882,911 mosquitoes), we parse the relative contributions of seasonality, temperature and land-type on mosquito abundance, identifying significant interactions between seasonality and land-type. In both cases, GAMs produce simple, yet flexible products that can link real world vector abundance data to transmission models, increasing accuracy and utility to models used to inform both epidemiology and public policy.”
Reiner received his doctorate in statistics in 2010 from the University of Michigan, Ann Arbor. He began his academic studies in California, where he earned his bachelor’s degree in applied mathematics in 2002 from UC Berkeley. He went on to obtain his master’s degree in applied mathematics from California State University, Northrdige, in 2005; and his master’s in statistics from the University of Michigan in 2009.
Plans are to record the seminar for later posting on UCTV.
Related Links:
Dengue Higher Than Previously Estimated (Thomas Scott lab)
List of Upcoming Seminars Sponsored by the UC Davis Department of Entomology and Nematology