Epidemics of dengue virus are linked to temperature rises of El Niño, a periodic weather phenomenon that coincides with warmer sea surface temperatures across parts of the equatorial Pacific.
This was the conclusion an international team reached after it analyzed continental-scale patterns of dengue that swept through eight countries of Southeast Asia in 1997 and 1998 during an intense El Niño event.
The team - comprising scientists from 18 institutions around the world, including the ministries of health of the countries affected - analyzed a huge set of data spanning 18 years of monthly dengue surveillance on a total of 3.5 million reported cases.
The analysis - published in the Proceedings of the National Academy of Sciences - is timely in that the most intense El Niño in nearly 20 years is currently developing in the Pacific, suggesting it presages a surge in dengue cases throughout Southeast Asia early next year.
The senior author of the study is Derek Cummings, a biology professor who was with the Johns Hopkins Bloomberg School of Public Health in Baltimore, MD, when the study began and is now with the Emerging Pathogens Institute at the University of Florida.
Prof. Cummings says that while dengue infects large numbers of people in the tropics every year, rates of infection vary widely from year to year, and:
"During years of large incidence, the number of people requiring hospitalization and care can overwhelm health systems. If we can understand the factors that contribute to these increases, we can prepare for them and act to mitigate the impact of the disease."
Urban areas act as 'pacemakers' for the spread of dengue
- It is estimated that there are around 390 million cases of dengue worldwide each year
- Dengue hemorrhagic fever is a more severe form that can be fatal if not recognized and treated promptly
- The best way to prevent dengue in affected areas is to eliminate places where the dengue-carrying mosquitoes lay their eggs, such as artificial containers that hold water.
Every year, hundreds of millions of people in the tropics and subtropics are infected by the dengue virus, which is transmitted through the bites of mosquitoes - most commonly the Aedes aegypti mosquito. There are four strains of the virus, known as DENV1, -2, -3 and -4. There are no specific treatments and no vaccines as yet, although some are in development.
The new study makes two key discoveries: one is that increased temperature leads to increased rates of dengue across the region.
The other key discovery is that urban areas act as "pacemakers" for the spread of the disease and set up "traveling waves" of infection into rural areas.
Prof. Cummings says they were really struck by how synchronized the incidence of dengue was over such a large area, spanning thousands of kilometers, and notes that:
"It suggests that continued multi-country coordination of surveillance for dengue is critical to understanding patterns in each individual country."
Co-author Lam Sai Kit, a professor at the University of Malaya in Malaysia, says the findings should help us better understand the cyclical nature of dengue and improve early warning systems for emerging outbreaks in the region. He adds:
"Now that the new El Niño has started, these findings will help us prepare for a worst-case scenario, and immediate measures can be taken to counter its effect in the next few months."
Some parts of the world where dengue occurs have no electricity or running water and are far from hospitals with accurate diagnostic equipment. Medical News Today recently reported how scientists are developing an inexpensive, rapid paper-strip test that works like an over-the-counter pregnancy test to help diagnose dengue, Ebola and other diseases in the field.