DENGUE:EPIDEMIOLOGYPART II SCOTT B HALSTEAD, MD Director, Research PEDIATRIC DENGUE VACCINE INITIATIVE
EPIDEMIOLOGY • Risk factors for severe disease. • Sequential dengue infection (includes antigenic structure of virus) • Race • Age • Host genetic factors • Nutritional status • Sex
Race • Caucasian & Asian vs African. At least 5:11,2 • Guzman MG et al. AJTMH 42:179-184, 1990. • Halstead SB et al AJTMH 65:180, 2001
BLACKS ARE RELATIVELY RESISTANT TO SEVERE DENGUE ILLNESS • A human resistance gene seems to explain the observation that while all dengue virus types circulate in Africa no DHF/DSS cases or outbreaks of DF have been reported.
DENGUE NEUTRALIZING ANTIBODIES BY AGE IN 210 CHILDREN RESIDENT IN PORT AU PRINCE, HAITI, 1996. N =(46) (40) (36) (41) (27) (13) (10) (4)
DHF - EFFECT OF AGE, 1981 Cuba Outbreak GUZMAN MG et al. Int J Infect Dis 6:18, 2002
CAPILLARY FRAGILITY Gamble J et al. Biochem Soc Med Res Soc 98:211-6, 2000.
GENETIC ASSOCIATIONSSusceptibility Resistance HLA1: HLA-A*0207 HLA-A*0203 HLA-B*51 HLA-B*52 HLA A24 HLA A33 Vit D2: t allele/352 FcRγII3: DCSIGN4: CD 209 promoter TNFα5: TNF 308 1. Loke H et al. JID 184:1369-73, 2001 2. Stephens HA et al. Tissue Antigens 60:309-318, 2002. 3. Loke H et al. AJTMH 67:102-6, 2001 4. Sakuntabthai A et al. Nat Genetics 37:507-13, 2005 5. Fernandez-Mestre MT et al. Tissue Ag 64:468-72, 2004
Effect of nutritional status on dengue disease severity1 Well nourished children: highly susceptible to severe disease Malnourished: protected against severe disease (protein-calorie malnutrition grade 2 and 3) 1. Thisyakorn U et al. CID 16:295-297, 1993
DHF/DSS in infants, identical to but more severe than DHF/DSS in children • Higher case fatality rates, resuscitation requires more fluid per Kg body weight than in older children with 2o infection. • Hung NT et al AJTMH 72:370, 2005 • Circulating cytokines and cytokine levels during acute phase similar to those in older children during 2o infection. • Hung NT et al JID 189:221, 2004
WHY DO MATERNAL ANTIBODIES ENHANCE DENGUE DISEASE? CENTRAL ROLE OF MACROPHAGES IN SUPPORTING DENGUE INFECTIONS IN HUMANS
Dengue viruses are adapted to grow in dendritic cells, monocytes and macrophages. Complexed with antibodies dengue viruses enter FcR-bearing cells with great efficiency.
IMMUNE ENHANCEMENT OF DENGUE INFECTION(Antibody-Dependent Enhancement) • In the presence of dengue ADE antibody: • increased rate of infection • increase in the number of infected cells. • increased production of viruses per cell.
DEN 3 VIREMIA ●--● DSS ▲- ▲DHF □--□ DF LIBRATY DH et al JID 185:1213, 2002
Schematic distribution of dengue 2 viruses in blood and tissues of 31 rhesus monkeys.
In endemic areas, DHF/DSS annual outbreaks differ in severity and size.
WHY? • Possible effect of • ADE • Heterotypic immunity • Replacement of serotypes • Clade extinctions • These possibilities have been explored in mathematical models, most are based upon the hospital epidemiological data from Bangkok or all of Thailand.
EFFECT OF ADE ON EPIDEMIC CYCLES • “Enhancement of infection may generate a complex and persistent cyclical or chaotic epidemic behavior ….and coexistence of mutiple strains” • Ferguson N et al. The effect of antibody-dependent enhancement on the transmission dynamics and persistence of mutiple-strain pathogens.Proc Natl Acad Sci USA 96:790-4, 1999
EFFECT OF HETEROTYPIC IMMUNITY ON EPIDEMIC CYCLES • 8-10 year epidemic cycles are accompanied by clade extinctions. • Mathematical model suggests that heterotypic immunity is responsible. • Adams B et al PNAS 103: 14234-9, 2006
SEROTYPE REPLACEMENT • DENV -1 replaced DENV 2, 3, 4. Related to stochastic event due to low transmission in 1999-2000? • Thu HM et al. Myanmar denge outbreak associated with displacement of serotypes 2, 3 and 4 by dengue 1. Emerg Infect Dis 10:693-7, 2004.
CLADE EXTINCTIONS DUE TO STOCHASTIC EVENTS • In Myanmar, clades B and C of genotype I DENV -1 circulated with clade A genotype III during the 1990s. After 1998, clade A disappeared leaving only clades B and C. • Thu HM et al Lineage extinction and replacement in dengue type 1 virus populations are due to stochastic events rather than to natural selection. Virol 336:163-72, 2005. • In Thailand, clades of DENV -3 circulating prior to 1992 disappeared and were replaced by two lineages with common ancestor.Earlier extinctions, 1963, 1973? • Wittke V et al. Extinction and rapid replacement of strains of dengue 3 virus during an interepidemic period. Virol 301:148-156, 2002.