Unsolved Epidemiological Questions on Dengue/Dengue Hemorrhagic Fever - From Taiwan's Experiences to Global Control

Speaker:
Prof Chwan-Chuen King, Dr. P.H.
Institute of Epidemiology and Preventive Medicine, College of Public Health,
National Taiwan University, Taipei, Taiwan

Host:
Professor Duane Gubler
Director, Program in Emerging Infectious Diseases

Date:
Thursday, February 9, 2012

Time:
9.30 am to 10.30 am

Venue:
Amphitheatre, Level 2
Duke-NUS Graduate Medical School
8 College Road, Singapore 169857
(opposite Singapore General Hospital, Block 6/7)

Contact Person:
Ms Sandie Lim, Program in Emerging Infectious Diseases
Tel: 6516 7256 or Email: sandie.lim@duke-nus.edu.sg

Synopsis:
The numbers of reported dengue hemorrhagic fever (DHF) cases have been increasing globally in the past three decades. The mechanisms that can explain these epidemiological changes have remained enigma. Through epidemiological field observations, two past major hypotheses for DHF are: (1) primary infection due to viral virulence proposed by Dr. L Rosen and (2) secondary infection of heterologous serotypes of dengue viruses (DENV) with antibody-dependent enhancement (ADE) advocated by Dr. S Halstead. However, not all secondary infection of DENV resulted in DHF cases whereas primary infection of DENV resulting in DHF has been documented in Taiwan and other areas with dengue endemicity. Most interestingly, these two hypotheses have not yet fully explained the mechanisms in increasing epidemic severity caused by DENV with high sequence identities over time in the same epidemics or over years during cross-country spread.

In Taiwan, we found that the number of DHF cases increased during the latter part of the epidemics in 1998, 2002 and 2006. Additionally, DENV isolated late in the epidemic from members of the same family showed higher virus diversity based on quasispecies analysis, thus leading to higher viral load in DHF than DF patients. Recently, we have identified key epidemiologic conditions for increasing DHF cases, including longer duration per epidemic wave and higher transmission intensity. Recommendations helpful in global control to minimize numbers of DHF cases will be discussed.

Biography:
Dr. King, a professor at the Institute of Epidemiology & Preventive Medicine, Deputy Director of Global Health, National Taiwan University, has taught several courses of infectious diseases. Her research interests include epidemiology and pathogenesis of dengue and dengue hemorrhagic fever, surveillance of infectious diseases, epidemiologic changes and interspecies transmission of influenza viruses, and epidemiology and public health policies. She has been an advisor for the Centers for Disease Control in Taiwan on elimination of poliomyelitis, epidemiology & health policies of severe acute respiratory syndrome (SARS), and pandemic influenza preparedness. In the past, she had been a consultant for Liberal Education Program at the Minister of Education in Taiwan and a standing committee member for Science Monthly Journal published in Taiwan. Currently, she is also a free writer on issues of infectious disease and public health, science policies, and higher education.