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MSII Microbiology > Unit 2 - Arbovirus > Flashcards

Unit 2 - Arbovirus Flashcards

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1
Q

define what an arbovirus is

A

group of viruses transmitted by arthropod vectors

-ARthropod-BOrne

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2
Q

what are the 4 clinical syndromes that arboviruses can cause?

A
  1. systemic febrile illness
  2. fever with arthritis
  3. encephalitis
  4. hemorrhagic fever
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3
Q

what is important about RNA viruses?

A
  • all of the viral hemorrhagic fever (VHF) viruses
  • majority of highly pathogenic viruses that produce encephalitis, severe fibrile illnesses
  • all arboviruses (transmitted by ticks, mosquitoes)
  • many have animal reservoir or animal amplification transmission with humans as an incidental host
  • many are endemic with periods of epidemics
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4
Q

what are mosquito-borne viruses that cause systemic febrile illness?

A
  1. chikungunya
  2. O’nyong-nyong
  3. Ross river
  4. Dengue
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5
Q

what are mosquito-borne viruses that cause fever with arthritis?

A
  1. chikungunya
  2. Ross river
  3. O’nyong-nyong
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6
Q

what are mosquito-borne viruses that cause encephalitis?

A
  1. Japanese encephalitis
  2. West Nile virus
  3. Venezuelan/Eastern/Western equine encephalitis
  4. Murray Valley encephalitis
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7
Q

what are mosquito-borne viruses that cause hemorrhagic fever?

A
  1. yellow fever
  2. dengue
  3. Rift valley fever
  4. chikungunya
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8
Q

explain Eastern Equine Encephalitis virology

A

Togaviridae family of alphavirus (highest probability of getting EEE)

  • focal epidemics of EEE in Eastern USA
  • clinical manifestations are inapparent influenza-like illness to encephalitis
  • mortality rates are 50%
  • causes leukopenia, increased protein, lowered glucose, and inflammation/edema in thalamus area
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9
Q

what are the 4 encephalitic viruses in the alphavirus genus? where are they found? probability of developing? mortaility rates?

A

Eastern, Western, Venezuelan, and Everglades

  • EEE: Eastern USA; highest chance of getting; 50% mortality
  • WEE: Western USA; 5% mortality
  • VEE: endemic in South and North America; lowest chance of getting; 35% mortality
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10
Q

explain Japanese encephalitis virus description

A

Flaviviridae, +sense ssRNA

  • circulates as single serotype
  • 5 genotypes (I - V)
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11
Q

what are the 5 genotypes of Japanese encephalitis and where do each dominate?

A

I: N. Thailand, Cambodia, Korea
II: S. Thailand, Malaysia, Sarawak, Australia, Indonesia
III: Japan, China, Taiwan, Vietnam, Philippines, Sri Lanka, India, Nepal
-has 4 subgroups
IV: Indonesia
V: Singapore

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12
Q

explain the transmission cycle of JEV

A

Culex tritaeniorhynchus vector

  • night feeders on large domestic animals and birds
  • rice fields, marshes, water collections
  • rainy season marks highest transmission
  • -irrigation allows year-round transmission
  • vertical transmission and overwinter is possible
  • sexual transmission between mosquitoes
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13
Q

what are the natural hosts and accidental hosts for JEV?

A

natural: pig
- prolonged and high titer viremia, asymptomatic
- production of numerous uninfected offspring
- viral replication
natural: migrating birds and domestic fowl

accidental: humans and horses

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14
Q

what are the transmission patterns of JEV

A
  1. seasonal transmission (large epidemics)
    - Japan, China, Taiwan, Korea, N. Vietnam, Thailand, N. India, Nepal
  2. year round transmission (sporadic cases)
    - S. Vietnam, Thailand, India, Indonesia, Malaysia, Philippines, Sri Lanka
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15
Q

what is the epidemiology of JEV?

A
  • 50,000 cases each year (underreported)
  • 10,000 deaths each year
  • in JEV endemic areas:
  • -infection common with high seroprevalence rates
  • -annual incidence as high as 10-20 per 100,000
  • increasing in India and Nepal
  • inapparent to apparent infections 200-300 to 1
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16
Q

what are clinical features of JEV?

A
  • incubation period: 6-16 days
  • spectrum: febrile headache –> aseptic meningitis –> encephalitis (<1%)
  • prodrome (2-3 days): headache, fever, chills, anorexia, N/V, dizziness
  • acute (3-4 days): high fever/seizures, dull flat mask-like facies, unblinking eyes, tremor, hypertonia, rigidity, abnormal behavior, acute flaccid paralysis
  • subacute (7-10 days) and convalescent (4-7 weeks): tremors, paresis, incoordination, pathologic reflexes, lip smaking, rapidly changing CNS signs
17
Q

what is the prognosis of JEV?

A

poor

  • respiratory dysfunction, prolonged seizures and fever, albuminuria
  • infectious virus in CSF
  • low IgM in CSF
18
Q

is JEV preventable?

A

yes, 2 vaccines

19
Q

what is JE-Vax (Biken)?

A

JEV vaccine

  • mouse-brain derived vaccine with JE E-protein of Nakayama strain
  • 3 shot series results in long-term immunity
  • serious side effect is anaphylactic-like reaction (delayed and rare)
  • production has stopped
20
Q

what is IXIARO?

A

JEV vaccine from strain SA 14-14-2

  • virus suspension treated with protamine sulfate to remove contaminating DNA and proteins
  • purified virus inactivated by formaldehyde treatment
  • administered in 2 doses 28 days apart
21
Q

what are adverse reactions to yellow fever vaccine?

A

serious adverse reactions highest if >60 yo

  1. immediate hypersensitivity or anaphylactic reactions
  2. yellow fever vaccine associated neurologic disease (YEL-AND)
  3. yellow fever vaccine-associated viscerotropic disease (YEL-AVD)
22
Q

what happens in YEL-AVD?

A

yellow fever vaccine-associated viscerotropic disease

-febrile illness that starts 3-5 days after vaccination, and clinically resembles naturally acquired yellow fever

23
Q

yellow fever virology?

A

Flaviviridiae Flavivirus

  • single open reading frame of 10,233 nt, encoding 3 structural and 7 non-structural proteins
  • 1 serotype, 5 genotypes
24
Q

what do phylogenetic analysis of yellow fever tell us?

A

originated in Africa

  • divided into West and East lineages
  • West african lineage has progenitor imported into S. America and New world
25
Q

explain the seasonal incidence of yellow fever

A

annual cases in S. America 50-300, but in Africa 4000
-large outbreaks can cause 100,000 cases and 30,000 deaths in Africa (due to losing protection provided by mass preventive immunization campaigns)

26
Q

explain geographic localization of yellow fever?

A

tropical regions of Africa and S. America in Amazon, Orinoco, Magdalena valleys, Bolivia, Brazil, Colombia, Peru

27
Q

clinical features of acute period yellow fever

A

incubation period ranges 3-6 days

  • clinical spectrum manifests as mild, nonspecific, febrile illness to fulminating, sometimes fatal hemorrhagic disease
  • severe YF begins acutely with fever, chills, severe headache, lumbosacral pain, generalized myalgia, anorexia, N/V, minor gingival hemorrhages, epistaxis
  • bradycardia despite rising temperature (Faget’s syn)
  • symptoms last 3 days and period of viremia
28
Q

clinical features of hemorrhagic phase of yellow fever

A

“coffee-ground” hematemesis (vomito negro), melena, metorrhagia, petechiae, ecchymoses

  • volume depletion is secondary to vomiting and plasma leakage
  • renal failure manifested by increase in albuminuria and diminishing urine output
  • death (in 20-50% severe cases) on 7th to 10th day of illness (preceded by deepining jaundice, hemorrhages, rising pulse, hypotension, oliguria, azotemia)
  • hypothermia, agitated delirium, intractable hiccups, hypoglycemia, stupor, coma are terminal signs
  • leukpenia, elevation of bilirubin, serum transaminas levels, thrombocytopenia, prolonged PT and PTT, and ST-T wave changes in EKG
29
Q

what are clinical features of yellow fever convalescent phase?

A

prolonged convalescence can occur with profound asthenia lasting 1-2 weeks

  • late death, occuring at end of convalescence, or even weeks after complete recovery from acute illness, is rare phenomenon attributed to cardiac complications or renal failure
  • elevations of serum trasaminase levels can persist for at least 2 months after onset of acute illness
30
Q

what are Dengue virus virology?

A

Flavivirus Flaviviridae

  • 4 serotypes that are antigenically distinct (DEN-1/2/3/4)
  • genetic diversity and phylogenetics between each serotype
  • variations in virus virulence due to RNA virus mutations and recombination events
31
Q

what spreads Dengue virus?

A

urban Aedes aegypti mosquito

  • breeds in standing water
  • daytime feeder
  • humans are preferred host for blood meal
  • multiple probing for single blood meal
32
Q

what are clinical manifestations of Dengue fever?

A

after 2-7 day incubation period, high fever, headache, retrobulbar pain, lumbosacral aching pain, conjunctival congestion, facial flushing develops
-fever lasts 6 to 7 days with generalized myalgia, bone pain anorexia, nausea, vomiting, weakness, prostration
-generalized macular rash may appear on the first or second day
-following defervescence (day 3 to 5) a secondary rash,
maculopapular or morbilliform appears on the trunk and then spreads centripetally to the face and limbs but spares the soles and palms
-fever may rise again, creating the second phase of the saddleback course
-peripheral WBC count is depressed with an absolute granulocytopenia, and the platelet count may fall to less than 100,000/mm3

33
Q

what are clinical manifestations of dengue hemorrhagic fever (secondary dengue)

A
  • petechiae, epistaxis, intestinal bleeding, menorrhagia, positive tourniquet test
  • myocarditis may occur, and neurologic disorders
  • Reye’s syndrome reported to follow infection
  • prolonged convalescence may occur with generalized weakness, depression, bradycardia, and ventricular extrasystoles
34
Q

what is shock syndrome?

A

severe form of viral hemorrhagic fever that results from:

  • intravascular volume depletion from plasma leakage into third space and/or blood loss
  • cardiovascular collapse
35
Q

what is the most common arbovirus causing human infection in subtropical and tropical regions of the world?

A

dengue fever

MSII Microbiology (23 decks)

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