Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Lower transmission increases dengue deaths

05.02.2008
Epidemiological model solves apparent paradox in Thai data

A pair of researchers has answered a puzzle about why efforts to lower the transmission of dengue virus in Thailand have not resulted in decreases in the severe, life-threatening, form of the infection. In fact, it seems to have had just the opposite effect.

Katia Koelle, an assistant professor in biology at Duke University, and Yoshiro Nagao, a graduate student at Osaka University Graduate School of Medicine, examined dengue infection data from Thailand going back to 1981, and constructed a set of epidemiological models in an attempt to explain this strange pattern.

Normally, an infection of the mosquito-borne virus produces a few days of non-fatal fever. But in some cases, it results in dengue hemorrhagic fever (DHF), in which capillary bleeding kills about 10% of patients.

Koelle and Nagao wanted to understand why, when transmission rates had apparently dropped due to extensive mosquito control efforts, cases of dengue hemorrhagic fever actually increased, with the largest recorded DHF outbreak occurring in 2001.

The answer, which appears online the week of Feb. 4 in the Proceedings of the National Academy of Sciences, lies in the way the body builds immunity to the four strains of dengue, which is the world's most common mosquito-borne viral disease.

It was known that victims could not get reinfected with a dengue strain they had already experienced. They also were less likely to be ill again with another strain for about a year after a first dengue infection. This "cross-immunity" between strains wanes with time however, as immune system antibodies decrease in number.

In fact, after cross-immunity has faded, another strain of the virus is able to use the remaining low level of antibodies it finds to gain entry into cells, making the infection more severe and resulting more often in DHF.

What Nagao and Koelle zeroed in on with their models was the question of what happens during that year of cross-immunity. One model said the challenges of new strains of virus during that year are defeated by antibodies from the first strain, without creating immunity to the newer strains.

But this model fails to explain the increase in DHF with lower transmission rates. The model that did explain this counterintuitive pattern is one in which patients "sero-convert," or develop new antibodies to additional strains, if they are bitten during the cross-immunity period.

Koelle said that when transmission rates are higher, a person stands a better chance of being bitten by more than one strain during this period of cross-immunity. This results in seroconversion and broader immunity, making a person less likely to get a severe dengue infection after they are no longer protected by cross-immunity.

But when transmission rates fall, as they did in Thailand, fewer people are able to build a library of antibodies during that year of cross-immunity, leaving them susceptible to subsequent strains down the road.

In spite of this, Koelle said Thai officials need to keep up the heat on the disease-carriers to "get over the hump" on the epidemiological curve. If transmission were lowered still further, the chances of second and third infections leading to DHF would be dramatically reduced, she said.

"We're definitely at the point where we'd really like to see decreases in the infection rate that are substantial enough to reduce the overall number of dengue hemorrhagic fever cases," she said.

She notes that tough mosquito control is still the best course of action, because a reliable vaccine of all four strains of dengue is not yet available.

Karl Leif Bates | EurekAlert!
Further information:
http://www.duke.edu

More articles from Health and Medicine:

nachricht Inselspital: Fewer CT scans needed after cerebral bleeding
20.03.2019 | Universitätsspital Bern

nachricht Building blocks for new medications: the University of Graz is seeking a technology partner
19.03.2019 | Karl-Franzens-Universität Graz

All articles from Health and Medicine >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: New gene potentially involved in metastasis identified

Gene named after Roman goddess Minerva as immune cells get stuck in the fruit fly’s head

Cancers that display a specific combination of sugars, called T-antigen, are more likely to spread through the body and kill a patient. However, what regulates...

Im Focus: The taming of the light screw

DESY and MPSD scientists create high-order harmonics from solids with controlled polarization states, taking advantage of both crystal symmetry and attosecond electronic dynamics. The newly demonstrated technique might find intriguing applications in petahertz electronics and for spectroscopic studies of novel quantum materials.

The nonlinear process of high-order harmonic generation (HHG) in gases is one of the cornerstones of attosecond science (an attosecond is a billionth of a...

Im Focus: Magnetic micro-boats

Nano- and microtechnology are promising candidates not only for medical applications such as drug delivery but also for the creation of little robots or flexible integrated sensors. Scientists from the Max Planck Institute for Polymer Research (MPI-P) have created magnetic microparticles, with a newly developed method, that could pave the way for building micro-motors or guiding drugs in the human body to a target, like a tumor. The preparation of such structures as well as their remote-control can be regulated using magnetic fields and therefore can find application in an array of domains.

The magnetic properties of a material control how this material responds to the presence of a magnetic field. Iron oxide is the main component of rust but also...

Im Focus: Self-healing coating made of corn starch makes small scratches disappear through heat

Due to the special arrangement of its molecules, a new coating made of corn starch is able to repair small scratches by itself through heat: The cross-linking via ring-shaped molecules makes the material mobile, so that it compensates for the scratches and these disappear again.

Superficial micro-scratches on the car body or on other high-gloss surfaces are harmless, but annoying. Especially in the luxury segment such surfaces are...

Im Focus: Stellar cartography

The Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT) in Arizona released its first image of the surface magnetic field of another star. In a paper in the European journal Astronomy & Astrophysics, the PEPSI team presents a Zeeman- Doppler-Image of the surface of the magnetically active star II Pegasi.

A special technique allows astronomers to resolve the surfaces of faraway stars. Those are otherwise only seen as point sources, even in the largest telescopes...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

International Modelica Conference with 330 visitors from 21 countries at OTH Regensburg

11.03.2019 | Event News

Selection Completed: 580 Young Scientists from 88 Countries at the Lindau Nobel Laureate Meeting

01.03.2019 | Event News

LightMAT 2019 – 3rd International Conference on Light Materials – Science and Technology

28.02.2019 | Event News

 
Latest News

Searching for disappeared anti-matter: A successful start to measurements with Belle II

26.03.2019 | Physics and Astronomy

Extremely accurate measurements of atom states for quantum computing

26.03.2019 | Physics and Astronomy

Listening to the quantum vacuum

26.03.2019 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>