DENGUE VIRUS: NO ONE IS SAFE

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www.invivo.fiocruz.br/dengue/home_dengue.htm
DENGUE VIRUS NO ONE IS SAFE Caitlin Reed Smith
College April 29, 2005
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OVERVIEW OF THEMES

• Background Information
• Clinical Presentation Diagnosis
• Biology
• Vaccination Prospects
• Public Health

3
WHAT IS DENGUE?

• Flavivirus (type of arbovirus)
• Transmitted from Aedes aegypti and Aedes
  albopictus mosquitoes
• Four Serotypes (Dengue 1-4)

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DENGUE (contd)

• Three Manifestations
• 1. Dengue Fever
• 2. Dengue Hemorrhagic Fever
• 3. Dengue Shock Syndrome
• Leads to death in 5 of cases
• More dangerous if infected second time by
  different serotype

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WHY DO WE CARE ABOUT DENGUE?

• CDC Category A Infectious Disease
• Infects 50-100 million people every year
• About half the world lives in a hot zone
• Very hard to create vaccine
• Mosquito evolution
  threat to U.S.
• Global warming

http//klab.agsci.colostate.edu/aegypti/aegypti.ht
ml
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WHY NOW?

• Failed eradication attempt in the Americas in
  1970
• Previously unestablished serotypes are
  establishing themselves in various countries
• Recent Outbreaks
• 1. India, 2003
• 2. Hawaii, 2001
• 3. Taiwan, 2001
• 4. Puerto Rico, 1994-1995

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WHERE IS DENGUE FOUND?
www.traveldoctoronline.net/diseases/dengue.htm
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DENGUE TRANSMISSION
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HOW DENGUE SPREADS

• Mosquitoes transmit
• dengue to human dendritic
• cells
• 2. Dengue targets areas
• with high WBC counts
• (liver, spleen, lymph
• nodes, bone marrow, and
• glands)

3. Dengue enters WBCs lymphatic tissue
4. Dengue enters blood circulation
http//phil.cdc.gov/PHIL_Images/08051999/00004/den
gue_phf/sld006.htm
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CLINICAL PRESENTATION OF DENGUE
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SYMPTOMS OF DHF
GRADE I Fever with other symptoms such as
vomiting, headache, muscle and joint pain
positive tourniquet test is the only evidence of
hemorrhaging GRADE II Grade I symptoms
spontaneous bleeding GRADE III Failure of
circulatory system, clammy skin, rapid weak
pulse, restlessness GRADE IV Severe shock, no
measurable blood pressure or pulse Considered
Dengue Shock Syndrome (DSS)
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DENGUE GRADATION
http//w3.whosea.org/en/Section10/Section332/Secti
on554_2564.htm
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P E T E C H I A E
http//www.cdc.gov/ncidod/dvbid/dengue/slideset/se
t1/images/petechiae2-small.jpg
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P U R P U R A
http//www.pediatrics.wisc.edu/education/derm/tutb
/85m.jpg
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E C C H Y M O S I S
http//www-medlib.med.utah.edu/WebPath/ATHHTML/ATH
036.html
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NASAL HEMORRHAGING
http//www.cgste.mq/brainstorm/dengue/image/hemo.g
if
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BIOLOGY OF DENGUE
http//www.stanford.edu/group/virus/flavi/2000/den
g_em.jpg
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BASIC BIOLOGY

• Single, positive-stranded RNA surrounded by an
  icosahedral core
• 90 glycoprotein E dimers overly M proteins
• Protein E is most important characteristic of
  dengue

Modis, Ogata, Clements, et. al., 2004
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BASIC DENGUE GENOME
http//microvet.arizona.edu/Courses/MIC419/VaccPro
p05html/Dengue.html
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FUSION PROTEIN E
Modis, Ogata, et. al., 2004.
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IMMUNE RESPONSE
http//www.ethal.org.my/opencms/opencms/ethal/Imag
es/MedGeneralImages/Lymphocyte.jpg
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FIRST INFECTION

• Humoral and cellular immune response
• - Ab serum neutralizing levels increase
• - T-lymphocytes activated by dendritic cells
• - Memory cells develop antibodies to fight
  off future infection of same serotype

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SECOND INFECTION

• Antibody dependent enhancement
• - Enhancing immunoglobulin G (IgG) antibodies
• - Fc Receptors

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CELLULAR LEVEL OF DENGUE FUSION
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ENTRY INTO CELL

• Dengue infection
• Endosome entry pH change
• E protein conformational change
• Release of viral RNA into cell
• Replication further infection

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PROTEIN E CONFORMATIONAL CHANGE
PRE-FUSION
POST-FUSION
Modis, Ogata, et. al., 2004
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PROTEIN E INSERTION INTO PM
http//crystal.med.harvard.edu/cover_modis_vsmall.
jpg
Modis, Ogata, et. al., 2004.
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VIRAL REPLICATION
http//chen.bio.purdue.edu/images/flavi/viruslifec
ycle.jpg
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TO SUMMARIZE

• THE BODYS RESPONSE TO A DENGUE INFECTION

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DENGUE IN THE CELL

• Dendritic cell infection ? T-cell activation
• Previous infection increase in viral load and
  decrease in incubation period
• ADE is problem for 20 years after first infection

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PATHOGENIC STRATEGIES OF DENGUE

• Invades circulatory system, causing
• - vascular permeability
• - Disseminated intravascular
  coagulation
• - Potentially death

http//www.ehu.es/biomoleculas/PROT/blood-clot.gif
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DENGUE DIAGNOSIS
http//bensguide.gpo.gov/images/ben/ben_doctor.
jpg
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LABORATORY DIAGNOSIS OF DENGUE

• METHODS
• 1. Viral Isolation Characterization
• 2. Genomic Sequencing
• 3. Antibody Detection

www.synergene.net/de/images/dnasmall.jpg
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VIRAL ISOLATION CHARACTERIZATION

• Old Gold Standard
• Cell Culture (mammals mosquitoes)
• -Indirect Immunofluorescence
• Useful to study basic virology, epidemiology,
• and pathogenesis
• Impractical for rapid diagnosis treatment

http//www.cdc.gov/ncidod/dvbid/dengue/slideset/se
t1/image/virus-isolation-cell-culture2.jpg
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GENOMIC SEQUENCING

• Quicker, more reliable means of diagnosis
• NASBA method (RNA-specific amplification assay)
• RT-PCR method to provide most accuracy, uses
  5-3 nuclease oligonucleotide probe (which may
  not be able to distinguish among serotypes) new
  Gold Standard
• Beware of false-positives due to contamination

http//animal.intron.co.kr/Image/RT-pcr.gif
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ANTIBODY DETECTION

• Most common methods
• 1. Hemagglutinin inhibition test (HI test)
• 2. ELISA
• 3. Rapid immunochromatography test (commercial
  kits available)

http//webdb.dmsc.moph.go.th/ifc_nih/applications/
pics/Qualitative_test.jpg
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STOPPING DENGUE

• VACCINE DEVELOPMENT AND PUBLIC HEALTH STRATEGIES

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MOST PROMISING VACCINE

• ChimeriVax-Dengue
• - Tetravalent
• - Uses yellow fever vaccine as base
• - 92 of monkeys passed virulent
  virus challenge

Guirakoo, Pugachev, and Zhang, 2004
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WHAT ABOUT HUMANS?

• Tetravalent vaccine
• ChimeriVax-Dengue?
• 20 seroconversion rate
• More research necessary!

http//www.lung.ca/pneumonia/images/doc2.gif
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PUBLIC HEALTH STRATEGIES

• Vector Control
• Surveillance
• Preparation for outbreaks
• Research

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NON-BIOLOGICAL MEANS OF DECREASING THE INCIDENCE
OF DENGUE
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MOSQUITO NETS
w3.whosea.org/extrelations/ images/Bed20net.jpg
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NO MORE MOSQUITOES!
www.mosquitobarrier.com/ images/tincan.jpg
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ABOUT THAT STANDING WATER
www.headlice.org/ images/unsanitary.jpg
45
Children play in sewage in Nairobi's sprawling
Mukuru Kaiyaba slum.
http//www.alertnet.org/thefacts/reliefresources/1
08273140124.htm
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IMPEDIMENTS

• Still lack complete understanding of dengue virus
  virulence
• Social/socioeconomic
• Travel spreads different serotypes
• Demographic changes
• Decentralized and therefore weak public health
  systems

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