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microb - viruses > Mosquito Borne Viruses & Hantavirus > Flashcards

Mosquito Borne Viruses & Hantavirus Flashcards

1
Q

Examples of mosquito borne viruses + hantavirus

A
  1. Dengue virus (flavivirus)
  2. Alphavirus (Chikungunya) (togavirus)
  3. Japanese encephalitis (flavivirus)
  4. Hantavirus (bunyavirus)
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2
Q

Structure of dengue virus

A
  • enveloped, with glycoprotein containing antigenic determinants - group specific, subgroup specific & type specific
  • spherical virion, ssRNA
  • 4 serotypes/subgroups
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3
Q

Epidemiology of dengue virus

A
  • Aedes aegypti is the main vector, also Aedes albopictus

- man is the main reservoir, man-mosquito-man transmission

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4
Q

Pathophysiology of dengue

A
  1. First infection
    - primary type antibody response
    - neutralising IgM production against type specific antigens - IgG production - patient immune to infecting dengue serotypes, partial protection (3-6w) against other serotypes (cross reactive Abs)
  2. Second infection
    - IgG predominant, infection enhancing
    - patient protected against clinical disease subsequently
  3. Deposited in skin by biting mosquito vector - replicates at site of infection & local lymphatic tissue - viremia (up to 4-5 day after onset of symptoms) - virus replicates in mononuclear phagocytes
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5
Q

Clinical presentations of dengue virus

A
  • can be asymptomatic or symptomatic
    1. Undifferentiated fever (infants, young children)
    2. Dengue fever
    3. Dengue hemorrhagic fever/dengue shock syndrome
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6
Q

Features of dengue fever

A
  • abrupt onset of high fever
  • severe headache
  • retro-orbital pain
  • muscle & joint pains
  • rash
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7
Q

Features of dengue haemorrhagic fever/dengue shock syndrome

A
  • fever (acute onset, high, continuous, 2-7 d)
  • haemorrhagic manifestations: positive tourniquet test - petechiae (do not blanch), purpura, ecchymosis, epistaxis, gum bleeding, haematemesis, melaena
  • enlargement of liver
  • DSS - rapid & weak pulse w narrowing of pulse pressure/hypotension w cold clammy skin & restlessness (inadequate perfusion to brain)
  • DSS - occurs at time of/shortly after fall in temp (3-7d), acute abdominal pain shortly before onset of shock, warning signs of shocl - restlessness/lethargy, acute abdominal pain, cold extremities, skin congestion, oliguria
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8
Q

Pathogenesis of dengue haemorrhagic fever/dengue shock syndrome

A
  1. Viral virulence - varied strains in terms of pathogenic potential
  2. Immune enhancement involving infection-enhancing antibodies
    - DSS seen in (A) infants 1yr w 2nd dengue inf
    - in (A) - infants in first 6m protected by maternal, neutralizing Abs - as maternal IgG degrades - dengue neutralising Abs decrease to below protective level (relatively, Abs w enhancing activity reach peak)
    - in (B) - non neutralising Abs from immune complexes w replicating virus, attach to Fc receptors on mononuclear phagocytes, complex internalised, virus continues to replicate in infected cell, mobile cell spreads infection - infection activates phagocytes - release cytokines etc - increase vasc perm & disorder in haemostasis
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9
Q

Diagnosis of dengue virus (4)

A
  1. Virus isolation - live mosquitoes, cell cultures
  2. Serology - haemagglutination inhibition test; IgM & IgG ELISA; NS1 Ag - ELISA (viraemia)
  3. RT-PCR - serum (viraemia)
  4. FBC - DHF/DSS - thrombocytopaenia (<100,000/mm3), haemoconcentration due to loss of plasma (vasc perm) - increased haematocrit
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10
Q

Treatment of dengue virus (3)

A
  1. Live attenuated tetravalent vaccine - in clinical trial
  2. Control of vector mosquitoes - source reduction, adulticiding, health ed, law enforcement
  3. DSS/DHF - increased vasc perm - plasma leakage - correct by vol replacement - infuse plasma/plasma expander/electrolyte solution
    - symptomatic treatment - avoid salicylates (cause bleeding), use paracetamol
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11
Q

Features of chikungunya fever

A
  • alpha virus transmitted by bite of Aedes aegypti & Aedes albopictus
  • endemic in Indian subcontinent, outbreaks in Malaysia, Italy
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12
Q

Symptoms of chikungunya fever

A
  • fever
  • skin rash
  • arthralgia (joint pain)
  • arthritis
  • photophobia
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13
Q

Diagnosis of chikungunya fever (2)

A
  1. RT-PCR
  2. Serology

to differentiate from dengue: 1. Serology 2. Positive travel history + tend to present more with severe joint pain, dengue more with muscle aches (but not definitive)

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14
Q

Epidemiology of Japanese encephalitis

A
  • majority of infections inapparent
  • mainly in children < 15 years
  • epidemics in India, Thailand, Vietnam, China
  • transmitted among mosquitoes & vertebrate hosts - Culex tritaeniorhynchus & Culex gelidus; vertebrate hosts are amplifying hosts mainly domestic pigs & wading birds
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15
Q

Pathogenesis of Japanese encephalitis

A
  • Bite by infected mosquito - virus replicates locally in skin/lymphatics/endothelium of blood vessels - transient viraemia
  • if viraemia terminates before virus penetrates brain/virus destroys sufficient brain cells to produce overt encephalitis - infection will be asymptomatic/non-encephalitic, generalized, febrile illness
  • enters nervous system by - capillary seeding through endothelium into meninges & brain OR inf of nerve endings
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16
Q

Symptoms of Japanese encephalitis (5)

A
  1. Abrupt onset w fever, headache, malaise, drowsiness, vomiting, generalised convulsions
  2. Marked & increasing disturbances of sensorium & signs of meningeal irritation (neck rigidity, positive Kernig’s sign)
  3. CSF abnormalities - pleocytosis, elevated glucose content, raised protein
  4. Histopathology of brain: destruction of neurons & glial cells, perivascular infiltration with lymphocytes, sometimes local haemorrhage
  5. Motor weakness, mental backwardness, behaviour disorders
17
Q

Diagnosis of Japanese encephalitis

A

Detect IgM from CSF during encephalitis - ELISA

18
Q

Treatment of Japanese encephalitis

A

Inactivated vaccines from infected mouse brain

19
Q

Structure of hantavirus

A

Enveloped, spherical virion with trisegmented ssRNA

20
Q

Variations of hantavirus

A
  • Hantaan, Seoul, Puumala, Dobrava (HFRS)
  • Sin Nombre (HPS)
  • Prospect Hill (not associated with disease)
21
Q

Transmission of hantavirus

A
  • virus transmitted to humans by infected rodents
  • infection in rodents - asymptomatic & lifelong, shed in saliva, urine, faeces
  • transmission predominantly after infected rodent excreta are inhaled
22
Q

Clinical presentation of hantavirus (2)

A
  1. Haemorrhagic Fever with Renal Syndrome (HFRS)

2. Hantavirus Pulmonary Syndrome (HPS)

23
Q

Features of haemorrhagic fever with renal syndrome

A
  • Mild to severe (esp in Korea, China, Balkans - Dobrava virus)
  • Mild HFRS in Europe is also nephropathia epidemica (Puumala virus)
  • Phases of severe clinical course:
    1. Febrile - Sudden onset with influenza-like symptoms, petechiae, conjunctival haemorrhage
    2. Hypotensive - 3-7d later - tachycardia, vomiting, shock, further haemorrhagic signs - haemoconcentration, thrombocytopaenia, leukocytosis
    3. Oliguric - hypotension, severe hemorrhage, abnormal renal fn, most deaths in this phase
    4. Diuretic - +/- electrolyte imbalance
    5. Convalescent - prolonged
24
Q

Features of hantavirus pulmonary syndrome

A
  • fever, myalgia, variable respi symptoms eg-cough

- followed by abrupt onset of acute respiratory distress

25
Q

Diagnosis of hantavirus pulmonary syndrome

A

Detection of antibody (IgM & total) by indirect IF assay & ELISA

microb - viruses (10 decks)

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