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VIRAL ZOONOSES. ZOONOTIC VIRUSES TRANSMISSIBLE FROM ANIMALS ARTHROPODS often via a blood sucking arthropod VERTEBRATES bites, body fluids, inhalation etc. VIRAL ZOONOSES. PART I ARTHROPOD BORNE. transmission. arthropod vectors (blood sucking)
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VIRAL ZOONOSES • ZOONOTIC VIRUSES • TRANSMISSIBLE FROM ANIMALS • ARTHROPODS • often via a blood sucking arthropod • VERTEBRATES • bites, body fluids, inhalation etc
VIRAL ZOONOSES PART I ARTHROPOD BORNE
transmission • arthropod vectors (blood sucking) • Many arboviral diseases world wide (hundreds)
ARBOVIRUSES • FEBRILE DISEASES • ENCEPHALITIS • HEMORRHAGIC FEVERS
ARBOVIRUSES FAMILY ENVELOPE yes yes no SYMMETRY icosahedral helical icosahedral GENOME ssRNA (+ve) ssRNA (-ve) segmented dsRNA, segmented
Birds Mammals Humans
ARTHROPOD Habitat Diurnal activity Preferred host Annual activity Overwintering ability Transovarial transmission VERTEBRATE Migratory activity Persistence of viremia Clinical consequences Reservoir ? Dead end host?
PREVENTION • SURVEILLANCE • VECTOR CONTROL • REPELLENTS • CLOTHING • TIMING OF ACTIVITY (OR CANCELLATION) • VACCINE
vertebrate arthropod arthropod vertebrate human SYLVATIC (JUNGLE) CYCLE
human arthropod arthropod human URBAN CYCLE human cycle note: viruses which have a human cycle may also have a sylvatic/jungle cycle
OUTBREAKS • TEND TO BE SUMMER/EARLY FALL • SPORADIC • UNPREDICTABLE
ARBOVIRAL DISEASE • MANY DIFFERENT ARBOVIRUSES CAUSE DISEASE • OFTEN SUB-CLINICAL
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
RECOVERY • INTERFERON • CELL-MEDIATED IMMUNITY • ANTIBODY MAY PLAY A ROLE IN PREVENTING SPREAD DURING VIREMIC PHASE
DIAGNOSIS • Immunological techniques • RT-PCR for viral RNA
RESISTANCE • IgG
ARBOVIRUS ENCEPHALITIS • SPORADIC • LOW % INFECTIONS -> CLINICAL CASES • NOT ALL CASES -> MAJOR DISEASE • PROBABLY UNDERDIAGNOSED
WEST NILE VIRUS • Reservoir: birds • Vector: mosquito • human, horse • dead end hosts flavivirus http://www.cdc.gov/ncidod/dvbid/westnile/cycle.htm
flavivirus West Nile virus
Final 2008 West Nile Virus activity in the United States flavivirus West Nile virus
WEST NILE VIRUS • Symptoms: • Fever • Meningitis • Encephalitis More rarely: • Acute flaccid paralysis • West Nile polio-like paralysis • poliomyelitis - inflammation spinal cord flavivirus http://www.cdc.gov/ncidod/dvbid/westnile/cycle.htm
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
WEST NILE VIRUS 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 flavivirus
http://www.cdc.gov/ncidod/dvbid/westnile/resources/wnv_transplant%20brochure6_12_07.pdfhttp://www.cdc.gov/ncidod/dvbid/westnile/resources/wnv_transplant%20brochure6_12_07.pdf
WEST NILE VIRUS transmission: • Mosquito (vast majority of cases) • Blood transfusion (blood supply is now screened) • Organ donation flavivirus
flavivirus 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%
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
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
EASTERN EQUINE ENCEPHALITIS CDC togavirus
WESTERN EQUINE ENCEPALITIS • Reservoir: birds • Vector: mosquito • Sentinels • horse,quail, turkey • Children at higher risk • CFR 3-5% • humans and horses dead end hosts USA: last confirmed human case 1999 togavirus
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
bunyavirus 2000 - 2 cases in SC, Charleston area La Crosse life cycle
ARBOVIRUSES – FEVER AND HEMORRHAGIC FEVER FAMILY FLAVIVIRIDAE Dengue Yellow fever REOVIRIDAE Colorado tick fever MAIN DISEASES fever, hemorrhagic fever hemorrhagic fever fever DISTRIBUTION World wide, especially tropics Africa, S. and C. America North America
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
flavivirus 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 http://news.bbc.co.uk/2/hi/americas/6422319.stm patients being treated for Dengue fever in a Paraguayan hospital
flavivirus 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 DENGUE HEMORRHAGIC FEVER/DENGUE SHOCK SYNDROME • hemorrhages • plasma leakage • hemoconcentration • hypotension • circulatory failure • shock
flavivirus CDC DHF - petechiae
Dengue hemorrhagic fever - pleural effusion CDC Vaughn DW et al. J Infect Dis 1997; 176:322-30.
flavivirus 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 DENGUE HEMORRHAGIC FEVER • Immune enhancement hypothesis • more mononuclear cells infected • infected monocytes release vasoactive mediators • increased vascular permeability • hemorrhagic symptoms
flavivirus 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 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 CDC last yellow fever epidemic in US - 1905