XML Feed for RxPG News   Add RxPG News Headlines to My Yahoo!   Javascript Syndication for RxPG News

Research Health World General
 
  Home
 
 Latest Research
 Cancer
 Psychiatry
 Genetics
 Surgery
 Aging
 Ophthalmology
 Gynaecology
 Neurosciences
 Pharmacology
 Cardiology
 Obstetrics
 Infectious Diseases
  AIDS
  Influenza
  MRSA
  Tuberculosis
  Shigella
  HCV
  SARS
  Ebola
  Dengue
  Malaria
  Pertussis
  Mumps
  Prion Diseases
  Small Pox
  Anthrax
  Leishmaniasis
 Respiratory Medicine
 Pathology
 Endocrinology
 Immunology
 Nephrology
 Gastroenterology
 Biotechnology
 Radiology
 Dermatology
 Microbiology
 Haematology
 Dental
 ENT
 Environment
 Embryology
 Orthopedics
 Metabolism
 Anaethesia
 Paediatrics
 Public Health
 Urology
 Musculoskeletal
 Clinical Trials
 Physiology
 Biochemistry
 Cytology
 Traumatology
 Rheumatology
 
 Medical News
 Health
 Opinion
 Healthcare
 Professionals
 Launch
 Awards & Prizes
 
 Careers
 Medical
 Nursing
 Dental
 
 Special Topics
 Euthanasia
 Ethics
 Evolution
 Odd Medical News
 Feature
 
 World News
 Tsunami
 Epidemics
 Climate
 Business
Search

Last Updated: Aug 19th, 2006 - 22:18:38

Dengue Channel
subscribe to Dengue newsletter

Latest Research : Infectious Diseases : Dengue

   DISCUSS   |   EMAIL   |   PRINT
Explaining peaks and troughs of dengue epidemics
Jul 31, 2006, 11:31, Reviewed by: Dr. Priya Saxena

"Until now, it's been very much a single-host, single-pathogen type of framework. Now with avian influenza being very much on everyone's mind, we're beginning to realize that the genetic diversity of infectious agents is really important."

 
Scientists have long known that epidemics of dengue fever wax and wane over a period of several years, but they've never been quite sure why. With the incidence and range of the potentially deadly mosquito-borne illness increasing, understanding the factors that influence these epidemics has never been more important.

A new study by researchers at the University of Georgia suggests that a brief period of cross-immunity conferred by any one of the four viral strains, or serotypes, that cause dengue explains the timing of epidemics.

"We found that since about the mid 1980s, there's been a sequential replacement of the dominant serotype," said lead author Helen Wearing, a post-doctoral researcher at the UGA Institute of Ecology. "So, for example, one year serotype three is 60 percent of the cases and the next year serotype two is dominant and so on. Epidemics of individual serotypes recur every eight to 10 years, but, at the same time, if you look at all the data together, you see about an average three-year cycle with some seasonal component to it."

In addition to helping resolve a long-standing debate in public health, the study, published this week in the early online edition of the journal Proceedings of the National Academy of Sciences, gives researchers a framework that can be used to create models that predict dengue outbreaks in both space and time.

"It's a framework that highlights the key elements you need to take into account while developing a forecasting model," Wearing said. "Because if you were to build a forecasting model without understanding the trends in cross-immunity, you would not necessarily predict what we observe."

The researchers examined 30 years of data from the government of Thailand and from a Thai clinic that keeps what is widely regarded as the most comprehensive set of data on dengue. Southeast Asia has been a dengue hot spot since the 1950s, but the researchers note that their model applies to other regions where all four dengue strains circulate.

The researchers compared the data with results from mathematical models that explore both independently and collectively the role factors such as temporary cross-immunity and variation in serotype virulence play in epidemics. They found that cross-immunity alone is enough to create the patterns that are observed in nature.

The study is a major departure from other theories about what drives dengue epidemics. The conventional wisdom is that an amplification of the severity of disease caused by repeat infections with different strains, a phenomenon known as antibody-dependent enhancement, drives the boom and bust cycles of dengue epidemics.

"Temporary cross-immunity has been ignored by the epidemiological community," said study co-author Pejman Rohani, associate professor of ecology and UGA Biomedical and Health Sciences Institute researcher.

"It's discussed in the scientific literature," Wearing added, "but no one ever considers it an important factor in generating the epidemiological cycles."

Cross-immunity, which lasts from two to nine months, results when overall antibody levels created by the body in response to infection by one serotype are high enough to protect against infection by related serotypes. After this period, however, antibody levels drop to levels that are no longer neutralizing but instead are exploited by the dengue virus to enhance replication and cause more severe illness.

"You can't deny the empirical fact that people who get severe dengue may well have had cases before," Rohani said. "But our work suggests it's not the mechanism that's underlying the big-picture pattern that we see."

Several factors are contributing to an increase in dengue epidemics. Global warming is allowing the species primarily responsible for spreading dengue (Aedes aegypti, also known as the yellow fever mosquito) to expand its range. Population growth in developing nations is pushing more people into substandard housing in mosquito-infested areas. And the ease of travel brings the virus to areas that were previously dengue-free when a mosquito bites an infected traveler and then spreads it to others. According to the Centers for Disease Control and Prevention, Aedes aegypti and the related Aedes albopictus (the Asian tiger mosquito) have the potential to spread dengue in sporadic outbreaks in the Southern and Southeastern United States.

Rohani said the same modeling techniques he and Wearing used to study dengue can help shed light on the transmission of other multi-strain diseases such as cholera, malaria and influenza. He calls a better understanding of such diseases, "one of the most important issues in public health and epidemiology in general."

"Until now, it's been very much a single-host, single-pathogen type of framework," Rohani said. "Now with avian influenza being very much on everyone's mind, we're beginning to realize that the genetic diversity of infectious agents is really important."
 

- Proceedings of the National Academy of Sciences
 

www.uga.edu

 
Subscribe to Dengue Newsletter
E-mail Address:

 



Related Dengue News

Explaining peaks and troughs of dengue epidemics
Genetically engineered mosquitoes show resistance to dengue fever virus
The Complicated Art of Tracking Dengue


For any corrections of factual information, to contact the editors or to send any medical news or health news press releases, use feedback form

Top of Page

 

© Copyright 2004 onwards by RxPG Medical Solutions Private Limited
Contact Us