www.invivo.fiocruz.br/dengue/home_dengue.htm
DENGUE VIRUS: NO ONE
IS SAFE
Caitlin Reed
Smith College
April 29, 2005
OVERVIEW OF THEMES
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Background Information
Clinical Presentation & Diagnosis
Biology
Vaccination Prospects
Public Health
WHAT IS DENGUE?
 Flavivirus (type of arbovirus)
 Transmitted from Aedes aegypti and Aedes
albopictus mosquitoes
 Four Serotypes (Dengue 1-4)
DENGUE (cont’d)
 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
WHY DO WE CARE ABOUT
DENGUE?
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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.html
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
WHERE IS DENGUE FOUND?
www.traveldoctoronline.net/diseases/dengue.htm
DENGUE
TRANSMISSION
HOW DENGUE SPREADS
1. Mosquitoes transmit
dengue to human dendritic
cells
2. Dengue targets areas
with high WBC counts
(liver, spleen, lymph
nodes, bone marrow, and
glands)
1
2
4
33
3. Dengue enters
WBCs & lymphatic
tissue
4. Dengue enters blood
circulation
http://phil.cdc.gov/PHIL_Images/08051999/00004/dengue_phf/sld006.htm
CLINICAL
PRESENTATION
OF DENGUE
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)
DENGUE GRADATION
http://w3.whosea.org/en/Section10/Section332/Section554_2564.htm
PETECHIAE
http://www.cdc.gov/ncidod/dvbid/dengue/slideset/set1/images/petechiae2-small.jpg
PURPURA
http://www.pediatrics.wisc.edu/education/derm/tutb/85m.jpg
ECCHYMOSIS
http://www-medlib.med.utah.edu/WebPath/ATHHTML/ATH036.html
NASAL HEMORRHAGING
http://www.cgste.mq/brainstorm/dengue/image/hemo.gif
BIOLOGY OF
DENGUE
http://www.stanford.edu/group/virus/flavi/2000/deng_em.jpg
BASIC BIOLOGY

Single, positive-stranded
RNA surrounded by an
icosahedral core
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90 glycoprotein E dimers
overly M proteins

Protein E is most
important characteristic
of dengue
Modis, Ogata, Clements, et. al., 2004
BASIC DENGUE GENOME
http://microvet.arizona.edu/Courses/MIC419/VaccProp05html/Dengue.html
FUSION PROTEIN E
Modis, Ogata, et. al., 2004.
IMMUNE
RESPONSE
http://www.ethal.org.my/opencms/opencms/ethal/Images/MedGeneralImages/Lymphocyte.jpg
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
SECOND INFECTION
 Antibody dependent enhancement
- Enhancing immunoglobulin G (IgG)
antibodies
- Fc Receptors
CELLULAR
LEVEL OF
DENGUE
FUSION
ENTRY INTO CELL
Dengue infection
Endosome entry & pH change
E protein conformational change
Release of viral RNA into cell
Replication & further infection
PROTEIN E CONFORMATIONAL
CHANGE
PRE-FUSION
POST-FUSION
Modis, Ogata, et. al., 2004
PROTEIN E INSERTION INTO PM
Modis, Ogata, et. al., 2004.
http://crystal.med.harvard.edu/cover_modis_vsmall.jpg
VIRAL REPLICATION
http://chen.bio.purdue.edu/images/flavi/viruslifecycle.jpg
TO
SUMMARIZE…
THE BODY’S RESPONSE
TO A DENGUE
INFECTION
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
DENGUE DIAGNOSIS
http://bensguide.gpo.gov/images/ben/ben_doctor.jpg
LABORATORY DIAGNOSIS OF
DENGUE
 METHODS:
1. Viral Isolation & Characterization
2. Genomic Sequencing
3. Antibody Detection
www.synergene.net/de/images/dnasmall.jpg
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/set1/image/
virus-isolation-cell-culture2.jpg
GENOMIC SEQUENCING
 Quicker, more reliable
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

means of diagnosis
NASBA method (RNAspecific 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
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/Qualitati
ve_test.jpg
STOPPING
DENGUE
VACCINE DEVELOPMENT
AND PUBLIC HEALTH
STRATEGIES
MOST PROMISING VACCINE
 ChimeriVax-Dengue
- Tetravalent
- Uses yellow fever
vaccine as base
- 92% of monkeys
passed “virulent
virus challenge”
Guirakoo, Pugachev, and Zhang, 2004
WHAT ABOUT HUMANS?
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Tetravalent vaccine
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ChimeriVax-Dengue?
20% seroconversion rate
More research necessary!
http://www.lung.ca/pneumonia/images/doc2.gif
PUBLIC HEALTH
STRATEGIES
 Vector Control
 Surveillance
 Preparation for outbreaks
 Research
NON-BIOLOGICAL MEANS OF
DECREASING THE
INCIDENCE OF DENGUE
MOSQUITO NETS
w3.whosea.org/extrelations/ images/Bed%20net.jpg
NO MORE MOSQUITOES!
www.mosquitobarrier.com/ images/tincan.jpg
ABOUT THAT STANDING WATER…
www.headlice.org/ images/unsanitary.jpg
“Children play in sewage in Nairobi's
sprawling Mukuru Kaiyaba slum.”
http://www.alertnet.org/thefacts/reliefresources/108273140124.htm
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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