Unsolved epidemiological questions on dengue/dengue hemorrhagic fever- From Taiwan's experiences to global control
Journal
International Journal of Infectious Diseases
Journal Volume
16
Pages
E90-E90
Date Issued
2012
Author(s)
Abstract
Background: The numbers of dengue hemorrhagic fever (DHF) have been increasing globally in recent 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 has frequently identified in Taiwan and other areas without 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 (Taiwan's 1998, 2001-2002, 2006 and 2009-2010 epidemics of dengue/DHF) or over years during cross-country spread. Methods: Viral load, DENV quasispecies and cytokines/chemokines were measured from DF and DHF patients. Results: We found that Taiwan's DHF cases in later period of epidemics of dengue/DHF in 1998, 2002 and 2006 showed more severe DHF cases. Additionally, DENV obtained from later cases of the same family member showed more virus diversity based on quasispecies analysis and thus leading to higher viral load in DHF than DF patients. Recently, our research team identified key epidemiologic conditions for increasing DHF cases, including longer duration per epidemic wave and higher transmission intensity of dengue cases in areas regardless high or low population density that would be very helpful in global control to minimize numbers of DHF cases. At present, we are investigating viral factors, immuno-attributes and entomologic transmission features with clear epidemiological characteristics and clinical findings in Kaohsiung's DENV-2 epidemic in Taiwan that might explain the increasing clinical and epidemiological severity of DHF over time periods not only in Taiwan but also in Cuba in 1981, 1997 and other South American countries. The preliminary results showed that both innate immunity and adaptive immunity contribute to immune-pathogenesis of DHF cases. Conclusion: In conclusion, evolution of dengue viruses might happen through epidemics with more influence of immunity at both individual and population levels.
SDGs
Publisher
Elsevier Sci Ltd
Type
meeting abstract