VIRAL HEAMORRHAGIC FEVERS Ahmed Mandil Prof of Epidemiology Dept of Family

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VIRAL HEAMORRHAGIC FEVERS Ahmed
MandilProf of EpidemiologyDept of Family
Community MedicineCollege of Medicine, King Saud
University
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HEADLINES

• Examples
• Emerging Re-emerging infections
• Dengue Fever (DF) versus Dengue Hemorrhagic Fever
  (DHF)
• Cycle of Disease Transmission of DF
• DF Agent Vector
• DF / DHF Prevention and Control

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Common Viral Haemorrhagic Fevers

• Rift valley fever, Dengue fever, Lassa fever
• Ebola and Marburg viral disease
• Bolivian / Argentinean haemorrhagic fever
• Haemorrhagic fever with renal syndromes

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Factors contributing to the emergence and
re-emergence of arthropod-borne diseases (I)

• Major global demographic changes urbanization
  and population growth
• Sub-standard environmental sanitation that
  facilitates transmission of Aedes aegypti - borne
  disease
• (overcrowding in cities with poor
  sanitation)

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Factors contributing to the emergence and
re-emergence of arthropod-borne diseases (II)

• Increased travel by airplane resulting in
  frequent exchange of dengue viruses and other
  pathogens
• Inadequate mosquito control services
• The emergence of resistance to insecticides
  linked to their increased misuse.

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Dengue Fever Overview

• While 2.5 billion people are at risk of infection
  world-wide, an estimated 50 to 100 million cases
  of dengue fever (DF) and several hundred thousand
  cases of dengue hemorrhagic fever (DHF) occur per
  year
• DHF comprises 2-5 of secondary infections, with
  average case fatality rate of DHF is about 5
• In the last 20 years, dengue transmission and the
  frequency of dengue epidemics has increased
  greatly in most tropical countries, including
  Southwestern KSA, hence DF / DHF is considered a
  resurgent disease worldwide, especially in the
  tropics

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Risk Factors for DHF Occurrence

• Virus serotype greatest for DEN-2, followed by
  DEN-3, DEN-4 and DEN-1
• Pre-existing anti-dengue antibody
• previous infection
• maternal antibodies in infants
• Host genetics
• Age (fatal cases are among children and young
  adults).
• Higher risk in secondary infections
• Higher risk in locations with two or more
  serotypes circulating simultaneously at high
  levels (hyperendemic transmission)

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Cycle of Transmission

• Agent Dengue flaviviruses
• Reservoir human/mosquito cycle (urban tropical
  areas) monkeys / mosquito cycle (western African
  / southeast Asian forests)
• Portal of exit from reservoir-blood
• Mode of transmission bite of infective Aedes
  aegypti mosquito (indirect vector-borne), no
  person-to-person transmission
• Portal of entry skin-piercing-blood
• Susceptible host universal

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Agent Dengue Viruses

• Four closely related single-stranded RNA Dengue
  flavi-viruses (DEN-1, DEN-2, DEN-3 and DEN-4)
• Each serotype provides specific lifetime
  immunity, and short-term cross-immunity
• (A person can be infected as many as four
  times, once with each serotype)
• All serotypes can cause severe and fatal disease

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Transmission of Dengue Virusby Aedes aegypti
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Replication and Transmissionof Dengue Virus (I)
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Replication and Transmissionof Dengue Virus (II)
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Aedes aegypti Mosquito
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Aedes aegypti

• Dengue Fever is transmitted by infected female
  Aedes aegypti mosquito
• Primarily, it is a daytime feeder, highly
  domesticated tropical mosquito, lives around
  human habitation
• Lays eggs and produces larvae preferentially in
  artificial water containers inside and around the
  houses for example plastic containers, flower
  vases, buckets, used automobile tires,..

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Clinical Characteristicsof Dengue Fever

• Incubation period 3-14 days (commonly 4-7 days)
• Fever and rash (erythema, maculo-papular)
• Pain headache (intensive), muscles (myalgia),
  joints (arthralgia), retro-orbital, etc
• Nausea / vomiting
• Hemorrhagic manifestations DF (minor petechiae,
  epistaxis, gum-bleeding, gastro-intestinal) DHF
  (major increased vascular permeability, specific
  organs)

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Differential Diagnosis

• Other vector-borne diseases
• Other common maculo - papular rashes measles
  (rubeola), German measles (rubella), etc
• Other systemic febrile illnesses
• Influenza, leptospirosis, typhoid fever, scrub
  typhus, etc

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Lab Diagnosis

• Antigen detection virus detection during acute
  phase in blood / serum within 5 days of infection
• Antibody detection
• IgM capture ELISA,
• RT-PCR
• Culture in mosquito cell-lines,
• Immuno-flourescence,
• PCR with nucleotide sequencing to detect strains
  / genotypes

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Prevention

• The best preventive measure is vector control
• Personal protection against mosquito biting
• Screening doors and windows
• Protective clothing
• Application of mosquito repellents on exposed skin

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Vector Control Methods

• Biological control largely experimental, e.g.
  place certain fish in containers to feed on
  larvae
• Environmental control elimination of larval
  habitats covering water holding containers,
  discarding artificial containers,
• It is the most likely method to be effective in
  the long term.
• Chemical Control larvicides may be used to kill
  immature aquatic stages, but ultra-low volume
  fumigation is ineffective against adult
  mosquitoes as Aedes aegypti is fully domesticated
  and mosquitoes may have resistance to commercial
  aerosol sprays

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Community Participation

• Prevention and mosquito control through active
  community involvement and participation to reduce
  larval breeding sources is the key to success
• Public health education on the basics of dengue,
  e.g.
• Locations for mosquito-laying of eggs
• Link between larvae and adult mosquitoes
• Dengue transmission, clinical picture,
  management, vector control methods

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Dengue Vaccine?

• No licensed vaccine at present
• Effective vaccine must be tetravalent (against
  the 4 sero-types), where field testing of an
  attenuated tetravalent vaccine currently underway
• May immunize population against yellow fever, if
  dengue occurs near jungle foci, as the urban
  vector for both diseases is the same

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HEADLINES

• Examples
• Emerging Re-emerging infections
• Dengue Fever (DF) versus Dengue Hemorrhagic Fever
  (DHF)
• Cycle of Disease Transmission of DF
• DF Agent Vector
• DF / DHF Prevention and Control

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Further Information

1. World Health Organization (WHO)
   http//www.who.int/denguenet/
2. Centers for Disease Control Prevention (CDC)
   http//www.cdc.gov/ncidod/dvbid/dengue/
3. Halsted SB. Dengue Epidemiology. Pediatric Dengue
   Vaccine Initiative
4. Selvaraj I. Dengue and dengue hemorrhagic fever.
   India.

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Thank You