- 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
(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