DENGUE: EPIDEMIOLOGY PART 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 5:1 1,2 1.Guzman MG et al. AJTMH 42: , 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.

RACE - SANTIAGO DE CUBA OUTBREAK, 1997

DENGUE NEUTRALIZING ANTIBODIES BY AGE IN 210 CHILDREN RESIDENT IN PORT AU PRINCE, HAITI, N =(46) (40) (36) (41) (27) (13) (10) (4)

AGE

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 ASSOCIATIONS Susceptibility Resistance HLA 1 : HLA-A*0207 HLA-A*0203 HLA-B*51 HLA-B*52 HLA A24 HLA A33 Vit D 2 : t allele/352 FcRγII 3 : DCSIGN 4 : CD 209 promoter TNFα 5 : TNF Loke H et al. JID 184: , Stephens HA et al. Tissue Antigens 60: , Loke H et al. AJTMH 67:102-6, Sakuntabthai A et al. Nat Genetics 37:507-13, Fernandez-Mestre MT et al. Tissue Ag 64:468-72, 2004

NUTRITIONAL STATUS

NUTRITIONAL STATUS OF DHF CASES vs. CONTROLS

Effect of nutritional status on dengue disease severity 1 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: , 1993

SEX

SEX RATIOS BY DENGUE SYNDROME Bangkok Children’s Hospital,

DHF/DSS during primary dengue infections.

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 2 o infection. –Hung NT et al AJTMH 72:370, 2005 Circulating cytokines and cytokine levels during acute phase similar to those in older children during 2 o infection. –Hung NT et al JID 189:221, 2004

DSS in a 6 month-old infants with hepatomegaly. Vietnam

INFANT DHF/DSS

WHY DO MATERNAL ANTIBODIES ENHANCE DENGUE DISEASE? CENTRAL ROLE OF MACROPHAGES IN SUPPORTING DENGUE INFECTIONS IN HUMANS

Complexed with antibodies dengue viruses enter FcR-bearing cells with great efficiency. Dengue viruses are adapted to grow in dendritic cells, monocytes and macrophages.

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.

ADE IN HUMAN DENGUE: DEN virus load and disease severity

DEN 3 VIREMIA ●--● DSS ▲- ▲DHF □--□ DF LIBRATY DH et al JID 185:1213, 2002

DISEASE SEVERITY CORRELATES WITH CELLULAR INFECTION

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.

MYANMAR: VARYING CFR YEARCASESDEATHSCFR 19862, , , , , , ,

DENGUE VIRUSES, BANGKOK

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: , 2006

SEROTYPE REPLACEMENT DENV -1 replaced DENV 2, 3, 4. Related to stochastic event due to low transmission in ? –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, 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: , 2002.