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Temperature Fluctuations Affect Population Growth Rate of Dengue Mosquito
The PLOS ONE journal published “Effects of Fluctuating Daily Temperatures at Critical Thermal Extremes on Aedes aegypti Life-History Traits," written by lead author Lauren Carrington and four other scientists from Thomas Scott’s Mosquito Research Laboratory and the Center for Vectorborne Diseases (CVEC).
Their work analyzed how natural temperature fluctuations affect the population growth rate of the dengue mosquito. Basically, temperature effects on larval development time, larval survival and adult reproduction depend on the combination of mean temperature and the magnitude of fluctuations.
“The effect of temperature on insect biology is well understood under constant temperature conditions, but less so under more natural, fluctuation conditions,” said Carrington, who completed her three-year postdoctoral fellowship last December in the Scott lab and continues research projects with the lab. She is now based at the Nossal Institute for Global Health, University of Melbourne, Australia.
The research is expected to lead to greater accuracy of applications for mosquito surveillance and disease prevention.
“An improved understanding of mosquito responses to natural temperature variation,” Carrington said, “will enhance the effectiveness of vector control strategies, thereby reducing transmission of mosquito-borne diseases, such as dengue fever.” By using constant temperatures, scientists can under- or -over estimate values, she said.
“In the field, mosquitoes, and other insects, are exposed to a constantly changing environment, with fluctuations in temperature throughout the day, every day. In the lab, however, experimental protocols generally try to minimize as much variability as possible, and temperature is often the first element to be standardized.”
Co-authors are Veronica Armijos, Christopher Barker, Louis Lambrechts and Thomas Scott.
Dengue is spread by an infected female Aedes aegypti mosquito, a day-biting, limited flight-range mosquito that prefers human blood to develop its eggs. Dengue is caused by four distinct, but closely related, viruses and the most severe form of disease is life-threatening dengue hemorrhagic fever or DHF.
Some 500,000 people with severe dengue are hospitalized each year, according to the World Health Organization (WHO), and about 2.5 percent of those affected die.
“Dengue takes an enormous toll on human health worldwide, with as many as 4 billion people at risk—half of the world’s population--and 400 million new infections each year,” said Scott, a professor of entomology at UC Davis and active in CVEC.
Dengue mosquito, Aedes aegypti. (Photo courtesy of Centers for Disease Control and Prevention)
Trying to Control Dengue
It's not just high temperatures that play a significant role in the transmission of dengue, a deadly mosquito-borne disease that strikes millions of people in tropical and subtropical countries.
The size and pattern of fluctuations in daily temperature have a large effect on pathogens transmitted by mosquitoes, according to groundbreaking research published today in the Proceedings of the National Academy of Sciences.
The research, led by French, Thailand and U.S. scientists and conceived by medical entomologist Thomas Scott (right) of the UC Davis Department of Entomology, targets the transmission of spread of dengue.
Lead author Louis Lambrechts (left) of the Institut Pasteur, France, who did postdoctoral research in the Scott lab, points out that the influence of average temperatures on dengue virus transmission has long been known–the higher the temperature, the more efficient the virus transmission—but this is the first study linking temperature fluctuations to the transmission of the disease.
Dengue, transmitted by the daybiting Aedes aegypti mosquito, globally infects 50 to 100 million people yearly. At risk are some 2.5 to 3 billion people, primarily in tropical and sub-tropical countries. The most severe form of the disease, dengue haemorrhagic fever (DHF), strikes half a million a year and kills an estimated 5 percent, according to the Centers for Disease Control and Prevention.
Scott said the study helps to explain a long-standing enigma: “What are the underlying causes of seasonal fluctuations in dengue incidence?” Experiments showed that mosquitoes die faster and are less susceptible to virus infection under large temperature swings, which is typical of the low dengue season, than under moderate temperature variation, which is typical of the high dengue season.
Scott, a noted dengue expert whose goal is to save lives through research, surveillance and implementation of disease prevention strategies, has a longstanding interest in the factors that drive seasonal and annual fluctuations in diseases caused by mosquito-transmitted pathogens. “Traditional explanations for the seasonal increase in dengue are not consistent with my experience in Thailand, Peru, and Puerto Rico,” Scott said.
For more about the research, see the UC Davis Department of Entomology web page or access the PNAS paper.
The dengue mosquito, Aedes aegypti. (Photo courtesy of James Gathany, Centers for Disease Control and Prevention).
