Newswise — Human transmission of the mosquito-borne viruses dengue, Zika and chikungunya increases in environmental temperatures ranging from 64 to 93°F (18–34°C), with maximal transmission occurring in a range from 78 to 84°F (26–29°C), according to an analysis conducted by a national team of scientists led by Erin Mordecai, Ph.D., Stanford University, and including Upstate Medical University’s Anna Stewart Ibarra, Ph.D., M.P.A. The scientists found that the risk for infection decreased dramatically outside of these ranges.
This new finding aids public health officials worldwide as they develop early warning systems for these mosquito-borne viruses and create targeted public health interventions to reduce the risk of exposure to mosquitoes carrying dengue, Zika and chikungunya viruses.
The study, “Detecting the impact of temperature on transmission of Zika, dengue and chikungunya using mechanistic models,” was published April 27 in the journal PLOS Neglected Tropical Diseases. The research was funded by a grant from the Ecology and Evolution of Infectious Disease program of the U.S. National Science Foundation (NSF EEID).
“This study provides important evidence of the role of climate in determining outbreaks of these mosquito-borne diseases, which often have a greater impact on the most vulnerable urban communities,” said Steward Ibarra, an internationally recognized expert in the ecology of infectious diseases and director of the Latin America Research Program at Upstate’s Center for Global Health & Translational Science.
She adds that transmission of these mosquito-borne viruses in temperate areas is limited to at most three months per year even if vectors are present. “Such brief transmission windows limit the likelihood of major epidemics following disease introduction in temperate zones,” she said.
The team measured the impact of temperature on transmission by two of the most common species of mosquitoes that are capable of transmitting these viruses to humans: Aedes aegypti and Aedes albopictus, Researchers integrated the data from several laboratory experiments into a mathematical model of temperature-dependent transmission, subsequently comparing their findings with human incidence data on the three viruses at the country scale in the Americas from 2014 to 2016.
“Knowing the optimal temperature for disease transmission is critical for predicting future disease rates,” said Mordecai. Before this study, Mordecai said there was a wide range of temperature predictions from other research groups.
Stewart Ibarra is currently leading field studies in Ecuador to provide data to improve the models. She and her team are following a cohort of 240 households at four cities in southern coastal Ecuador over a three-year period. They are gathering data on dengue, Zika and chikungunya viral infections in people and mosquitoes, microclimate data from each home and data on other social-ecological risk factors such as housing conditions. These studies are funded by the NSF EEID grant and the NSF Zika Rapid grants.
Dengue, Zika and chikungunya viruses are transmitted by the bite of infected Aedes aegypti and Aedes albopictus mosquitoes. These mosquitos are primarily found in tropical and subtropical areas of the world.
To reduce the incidence of these viruses, public health officials suggest precautions that include: eliminate standing water in and around the home, use air conditioning when available, use screens on windows and doors, repair holes in screens, use EPA-registered insect repellent with one of the following ingredients: DEET, Picaridin, IR3535, oil of lemon eucalyptus (OLE) or para-menthane-diol (PMD), 2-undecanone.
Upstate Medical University’s Center for Global Health & Translational Science is targeting mosquito-borne viruses at various fronts through vaccine trials and epidemiological studies. Staff members are engaged in center-based and field-research projects in several countries around the world, including Ecuador, Thailand, Kenya and the United States.