- 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
If a patient is the sole wage earner in the family, lost wages can amount to a third of the monthly household income.
Olkowski recently gave a presentation on the "Economic Impact of Work Absenteeism Due to Dengue Fever in Iquitos, Peru” at the fifth annual American Society of Tropical Medicine Hygiene/Peru meeting.
“Over a quarter of the laboratory-confirmed patients fell significantly below Peru's minimum monthly wage,” Olkowski said. “In the wage group with the highest rate of dengue, lost wages due to dengue illness represented more than 25 to 30 percent of their monthly income. It's also important to note that we included only wage-earners, whereas the majority of women work in the home and are not earning a wage, so these are one-income households.”
“In this project, Dr. Vilcarromero and I quantified one aspect of the 'hidden economic burden' of dengue in Iquitos,” she said. “A lot of attention is being given to the economic impact of hospitalized dengue cases but that's not the full story. Our research demonstrates that even when dengue is technically a ‘mild' illness, the people who live with it are suffering not only physically but economically.”
“For this study, we looked at how lost work days due to non-severe dengue affects people,” Olkowski said, explaining that in Iquitos, most families have a single wage earner and receive little or no paid sick leave. “Thus, taking a sick day can mean less support for their families.”
“We considered only patients who went to a clinic but were not hospitalized and who were laboratory confirmed for dengue serotype 4,” she said. “That is generally considered to cause mild, ambulatory illness so that would probably not be taken too seriously from an economic impact standpoint.”
This was her third trip to Iquitos. On each of the first two trips, she did research for about two months, and has now been in Iquitos for seven months.
Olkowski, who is seeking her doctorate in entomology with a major interest in medical entomology and public health, expects to graduate in the summer of 2016. She holds a bachelor's degree in economics from UC Davis.
The world-class Thomas Scott lab studies the dengue virus, which is transmitted by Aedes aegypti, a daytime-biting mosquito. The dengue virus has been spreading globally over the last four decades, including parts of United States. More than half of the world's population is now at risk of infection. The disease infects 400 million people each year.
Scott, distinguished professor of entomology and director of the Mosquito Research Program, is the principal investigator of two grants totaling nearly $10 million to study the mosquito-borne, viral illness.
The grants, awarded in 2014, include $7.5 million from the National Institutes of Health (NIH) and $2.2 million from Notre Dame University.
Amy Morrison of the UC Davis Department of Entomology and Nematology, co-leads the projects in Iquitos, where she directs the long-running UC Davis epidemiological field research program in collaboration with NAMRU-6. Other UC Davis researchers involved in the grants are Steven Stoddard, Robert C. Reiner, T. Alex Perkins, Veronica Armijos, Jody Simpson and Christopher Barker and Olkowski.
The $2.2 million grant, “Spatial Repellants for Control of Vector-borne Disease,” from Notre Dame University, is the first-ever project aimed at dengue prevention. It focuses on studying the potential for spatial insect repellants to reduce exposure to dengue virus in people's homes.
The NIH grant, “Quantifying Heterogeneities in Dengue Virus Transmission Dynamics,” aims to quantify how much people, with different degrees of illness, vary in their contribution to virus transmission and spread.
- 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.
