viral zoonoses zoonotic viruses transmissible from animals
TRANSCRIPT
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VIRAL ZOONOSES
• ZOONOTIC VIRUSES– TRANSMISSIBLE FROM ANIMALS
• ARTHROPODS– often via a blood sucking arthropod
• VERTEBRATES– bites, body fluids, inhalation etc
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VIRAL ZOONOSES
PART I
ARTHROPOD BORNE
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transmission
• arthropod vectors (blood sucking)
• Many arboviral diseases world wide (hundreds)
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VIGILANCE
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• ARBOVIRUSES– FEBRILE DISEASES– ENCEPHALITIS– HEMORRHAGIC FEVERS
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ARBOVIRUSES
FAMILY ENVELOPE
yes
yes
no
SYMMETRY
icosahedral
helical
icosahedral
GENOME
ssRNA (+ve)
ssRNA (-ve)segmented
dsRNA, segmented
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BirdsMammalsHumans
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ARTHROPOD• Habitat• Diurnal activity• Preferred host• Annual activity• Overwintering ability• Transovarial
transmission
VERTEBRATE• Migratory activity• Persistence of
viremia• Clinical
consequences• Reservoir ?• Dead end host?
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PREVENTION
• SURVEILLANCE
• VECTOR CONTROL
• REPELLENTS
• CLOTHING
• TIMING OF ACTIVITY (OR CANCELLATION)
• VACCINE
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SYLVATIC (JUNGLE) CYCLE
arthropod arthropod
vertebrate human
vertebrate
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URBAN CYCLE
arthropod arthropod
human
human
human cycle
note: viruses which have a human cycle may also have a sylvatic/jungle cycle
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OUTBREAKS
• TEND TO BE SUMMER/EARLY FALL
• SPORADIC
• UNPREDICTABLE
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ARBOVIRAL DISEASE
• MANY DIFFERENT ARBOVIRUSES CAUSE DISEASE
• OFTEN SUB-CLINICAL
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ARBOVIRAL DISEASE
• INITIAL VIRAL REPLICATION– endothelial cells– macrophages/monocyte lineage
• INTERFERON (RNA VIRUSES)– headache, fever, myalgia
• VIREMIA– spread to target tissues, depending on
tropism of virus
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RECOVERY
• INTERFERON
• CELL-MEDIATED IMMUNITY
• ANTIBODY MAY PLAY A ROLE IN PREVENTING SPREAD DURING VIREMIC PHASE
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DIAGNOSIS
– Immunological techniques
– RT-PCR for viral RNA
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RESISTANCE
• IgG
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ARBOVIRUSES – ENCEPHALITIS
FAMILY DISTRIBUTION
FLAVIVIRIDAE
West Nile virus encephalitis North America, parts of Europe, parts of Africa
St Louis encephalitis North America
TOGAVIRIDAE
Eastern equine encephalitis East US, Canada
Western equine encephalitis West US, Canada, Mexico, Brazil
BUNYAVIRIDAE
California serogroup (La Crosse etc) North America
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ARBOVIRUS ENCEPHALITIS
• SPORADIC
• LOW % INFECTIONS -> CLINICAL CASES
• NOT ALL CASES -> MAJOR DISEASE
• PROBABLY UNDERDIAGNOSED
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WEST NILE VIRUS
http://www.cdc.gov/ncidod/dvbid/westnile/cycle.htm
• Reservoir: birds
• Vector: mosquito
• human, horse– dead end hosts
flavivirus
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1999
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flavivirusWest Nile virus
22flavivirusWest Nile virus
Final 2008 West Nile Virus activity in the United States
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WEST NILE VIRUS
http://www.cdc.gov/ncidod/dvbid/westnile/cycle.htm
• Symptoms:– Fever– Meningitis– Encephalitis
More rarely:– Acute flaccid paralysis
• West Nile polio-like paralysis– poliomyelitis - inflammation spinal cord
flavivirus
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West Nile Virus
For every ~150 people infected
– ~30 mild symptoms• mild fever, headache, body ache, maybe rash
– may never see physician, even if do, may not be diagnosed
– ~1 severe illness • e.g. encephalitis, meningitis, high fever, stiff neck,
stupor, disorientation, coma, tremors, convulsions, muscle weakness
– frequency of flaccid paralysis unknown, but much less than frequency of encephalitis
flavivirus
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Case fatality ratio:
• Seen in all age groups but higher in the elderly– the majority of cases of neuroinvasive
diseases and fatalities are over 50 yrs age
• Transplant recipients may be at higher risk– increased incidence of clinical disease– increased risk of severe disease
WEST NILE VIRUS
flavivirus
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http://www.cdc.gov/ncidod/dvbid/westnile/resources/wnv_transplant%20brochure6_12_07.pdf
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WEST NILE VIRUS
flavivirus
transmission:
• Mosquito (vast majority of cases)
• Blood transfusion (blood supply is now screened)
• Organ donation
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Reported Human WNV Disease Cases, US
1999 62
2000 21
2001 66
2002 4156
2003 9862
2004 2539
2005 3000
2006 4269
2007 3630
2008 1338
2009 515 (as of 10-20-09)
2008 Case Fatality Rate = 44/1356 = 3.2%
flavivirus
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ST. LOUIS ENCEPHALITIS
• Second commonest mosquito borne disease in US
• Reservoir: birds– Man is usually a dead end
host
• Vector: mosquito• <1% infections clinical• Elderly at higher risk• CFR 3-25%• ~100 cases/year av.
flavivirus
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EASTERN EQUINE ENCEPHALITIS
• Reservoir: birds• Vector: mosquito• Sentinels
– horse,quail, turkey
• Under 15yrs, over 50yrs at higher risk
• CFR ~35%• ~5 cases/year av.• horses and humans
dead end hosts
CDC
togavirus
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EASTERN EQUINE ENCEPHALITIS
CDC
togavirus
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WESTERN EQUINE ENCEPALITIS
• Reservoir: birds• Vector: mosquito• Sentinels
– horse,quail, turkey
• Children at higher risk
• CFR 3-5%• humans and horses
dead end hoststogavirus
USA: last confirmed human case 1999
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CALIFORNIA SEROGROUP ENCEPHALITIS(includes La Crosse virus)
• Recently commoner in eastern US
• Reservoir: small mammals
• Vector: mosquitos• Children at higher risk• Low CFR• ~80 cases/year av.
bunyavirus
34La Crosse life cycle
2000 - 2 cases in SC, Charleston area
bunyavirus
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ARBOVIRUSES – FEVER AND HEMORRHAGIC FEVER
FAMILY
FLAVIVIRIDAE
Dengue
Yellow fever
REOVIRIDAEColorado tick fever
DISTRIBUTION
World wide, especially tropics
Africa, S. and C. America
North America
MAIN DISEASES
fever, hemorrhagic fever
hemorrhagic fever
fever
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COLORADO TICK FEVER- coltivirus
Vector: tick
• Mild disease in man
• Fever, rash, arthralgia
• RMSF important consideration in differential diagnosis
• Probably common, rarely reported Reovirus family
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flavivirus
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DENGUE FEVER
• jungle cycle (monkeys-mosquitoes)• urban cycle (man-mosquitoes)• rapidly increasing disease in tropics• approx. 100-200 cases/yr in US due to import
– occasional indigenous transmission
• 50-100 million cases per year worldwide– ~900,000 cases in Central and S. America in 2007
flavivirus
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http://news.bbc.co.uk/2/hi/americas/6422319.stm
patients being treated for Dengue fever in a Paraguayan hospital
flavivirus
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DENGUE FEVER
• Fever (overlaps with viremic phase)• headache• retro-orbital pain• myalgia, arthralgia• severe joint and muscle pain
‘breakbone fever’• sometimes rash• may look like flu, measles, rubella• more rarely encephalitis
flavivirus
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DENGUE HEMORRHAGIC FEVER/DENGUE SHOCK
SYNDROME • hemorrhages
• plasma leakage
• hemoconcentration
• hypotension
• circulatory failure
• shock
flavivirus
42DHF - petechiae
CDC
flavivirus
43Dengue hemorrhagic fever - pleural effusion
CDCVaughn DW et al. J Infect Dis 1997; 176:322-30.
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DENGUE HEMORRHAGIC FEVER
• immunopathological
• 4 serotypes (1, 2, 3, 4)– increase in areas in which all 4 circulate has led to more
cases DHF fever in South and Central America– Entomologic, serologic and virologic conditions are now
such that locally acquired DHF can occur in South Texas
• maternal antibody flavivirus
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DENGUE HEMORRHAGIC FEVER
• Immune enhancement hypothesis– more mononuclear cells infected– infected monocytes release
vasoactive mediators– increased vascular permeability– hemorrhagic symptoms
flavivirus
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DENGUE HEMORRHAGIC FEVER
• do not give aspirin, ibuprofen – because of anticoagulant affects– (acetaminophen OK)
• children more severe disease
• CFR depends on rapid response– can be as low as 1%
flavivirus
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CDC
YELLOW FEVER
• jungle and urban cycles• hemorrhages• degeneration liver, kidney,
heart• CFR 50%• Vaccine (live attenuated)
– important to consider in travel to areas with yellow fever
– egg grown– contraindicated in immune
suppression
flaviviruslast yellow fever epidemic in US - 1905
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The end
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(Time Dec 2007)
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Aedes albopictus is a species of mosquito which is a good vector for Dengue
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WEST NILE VIRUS
flavivirus
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WEST NILE VIRUS
flavivirus
Case fatality ratio:
• Higher in elderly• The 1 fatality in SC in
2005 was over 65 years old
• Peaks about Aug-Sept
SC
SC - 2005
http://westnilemaps.usgs.gov/sc_human.html
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1999
West Nile virus
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2000
West Nile virus
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2001
West Nile virus
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2002
West Nile virus
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2003
West Nile virus
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2004
West Nile virus
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2005
West Nile virus
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2006
West Nile virus
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