- Author: Kathy Keatley Garvey
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.
- Author: Kathy Keatley Garvey
In an article published this week in the Proceedings of the National Academy of Sciences (PNAS), the UC Davis medical entomologists and their colleagues found that human movement—people going from house-to-house to visit their friends and relatives—is a key component to driving the virus transmission. (Read PNAS paper)
The research site is Iquitos, nestled in the heart of the Amazon rain forest of northeastern Peru. It's considered one of the world’s primary “open laboratories” to study the transmission of the virus.
The Aedes aegypti mosquito is a day-biting mosquito and we humans are its favorite host/target.
The ground-breaking research shows why it's crucial to focus on people movement, not just on the traditional mosquito control-and-prevention methods, such as applying insecticides and eliminating water-filled containers that can provide a larval habitat.
As lead author/medical entomologist Steve Stoddard said: "This finding has important implications for dengue prevention, challenging the appropriateness of current approaches to vector control."
“Interestingly, it didn’t matter how far away the visited houses were," Stoddard said. "The mosquito that transmits dengue virus prefers to stay in small areas, say in less than a 100-meter radius, but the distance between houses was often much greater than this. So it only makes sense that humans are frequently spreading the virus around as they commute between their homes and the homes of their friends and family. Altogether the data demonstrate what we expected, that human movements are really key to the transmission of this mosquito-borne virus.”
Said Scott, professor of entomology at UC Davis and director of the Mosquito Research Laboratory: “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. The results from our study are focusing attention to the role human social networks in virus invasion and epidemic spread.
"At our Peru study area, we found that infection risk is based on the places a person visits and transmission dynamics are driven by overlapping movements of people who recently visited the same places, like the homes of their family and friends.”
Bottom line: The scientists found that people movement not only defined individual infection risk and local patterns of incidence, but resulted in the rapid spread of the virus and marked heterogeneity in transmission rates.
Next phase of the research? It's aimed at "understanding how variation in human behavior influences transmission and applying that knowledge in enhanced disease prevention strategies,” said Scott, the principal investigator of a National Institutes of Health (NIH)-funded grant.
With some 4 billion people worldwide at risk, and with 400,000 million new infections each year, dengue is indeed taking its toll. Every year some 500,000 people with severe dengue are hospitalized, and 2.5 percent die.