The mosquito transmits the Zika virus, currently "the" hot medical topic.
But it also transmits dengue, yellow fever and chikungunya viruses.
“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,” says medical entomologist Thomas Scott, distinguished professor and now emeritus, UC Davis Department of Entomology and Nematology.
Scott, who has studied dengue more than 25 years and is recognized as the leading expert in the ecology and epidemiology of the disease, emphasizes that “There is no vaccine nor drug that is effective against this virus." There are four serotypes: DENV-1 through DENV-4.
Now for the groundbreaking news.
Scott and his colleagues just published a study in the Public Library of Science (PLOS), Neglected Tropical Diseases, that is sure to rock the world of everyone who has ever contracted dengue.
Well, yes, you can. "Lifetime of immunity" is false.
“Our most significant result from this study is that immunity to dengue viruses does not always provide perfect protection from reinfection,” Scott said. “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.”
“Our data indicate 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.”
Former UC Davis researcher Steve Stoddard and senior author of the paper said it well:
“It has long been thought that infection with any one of the viruses produced lifetime immunity to that virus. This finding could help explain results of dengue vaccine trials that showed poor efficacy against one of the four serotype. 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.
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.
The target: the dengue mosquito.
The occasion: A UC Davis Department of Entomology seminar.
Wong, now a postdoctoral fellow with the Centers for Diseases Control and Prevention, Atlanta, Ga., will discuss her research on "Oviposition Site Selection by Aedes aegypti and its Implications for Dengue Control” from 12:10 to 1 p.m., Wednesday, Sept. 28 in Briggs Hall.
Her dissertation research, completed in Iquitos, Peru, focused on the egg-laying behavior of Aedes aegypti, the principal mosquito vector of dengue viruses.
A former resident of San Luis Obispo, Wong received her bachelor’s degree in molecular and cell biology from UC Berkeley in 2001 and her master’s degree in epidemiology from UC Davis in 2006.
Next up in the fall seminar series: On Wednesday, Oct. 5 Judith Becerra, associate research professor, University of Arizona, Tucson, will speak on “Coevolution between Bursera and its Herbivores.”
Then on Wednesday, Oct. 12, the speaker is Lynn Kimsey, director of the Bohart Museum of Entomology and professor of entomology at UC Davis. She will discuss "The International Cooperative Biodiversity Group Program (ICBG) Rain Forest Expedition to Sulawesi Rainforest.” Kimsey's discovery of a new "warrior wasp" species recently made international news.
Assistant professors Louie Yang and Johanna Chiu have compiled an excellent schedule of speakers. Most will be webcast. See the complete list.