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MICR3320 > 20 - Vector Borne Viral Diseases > Flashcards

20 - Vector Borne Viral Diseases Flashcards

1
Q

Three families that most arboviruses causing human disease belong to

A
  • Togaviridae (Alphavirus)
  • Flaviviridae (Flavivirus)
  • Bunyaviridae (Bunyavirus)
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2
Q

Alphaviruses and flaviviruses

A
  • Enveloped
  • Linear
  • (+)ssRNA
  • Spherical
  • Underlying capsid
  • Measure 40-70nm
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3
Q

Bunyaviruses

A
  • Enveloped
  • Circular
  • (-)ssRNA
  • Spherical
  • Segmented
  • 80-120nm in diameter
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4
Q

Alphaviruses subdivisions

A

Divided into those associated with polyarthritis and rash (mainly old world strains) and those associated with meningoencephalitis (mainly new world)

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5
Q

Old world alphavirus strains

A
  • CHIKV
  • o’nyongnyong virus
  • Ross river
  • Sindbis
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6
Q

Alphavirus replication cycle

A
  • Virus binds to host receptor via E1 and E2 glycoproteins
  • Clathrin dependent endocytosis occurs and nonstructural proteins are translated first from the full-length viral RNA, allowing assemblage of the viral replication complex.
  • The structural proteins are translated from the subgenomic RNA.
  • The capsid protein assembles into NCs with the full- length viral RNA.
  • pE2, 6K and E1 insert into the endoplasmic reticulum membrane and transit to the host plasma membrane via the secretory pathway.
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7
Q

Chikungunya Virus

A
  • 11.5kb enveloped (+) ssRNA
  • Alphavirus genus, Togaviridae family
  • Aedes (Ae.) mosquitos
  • E1-A226V mutation in Ae albopictus leads to increased infectivity and transmissibility
  • Sylvatic and urban cycles
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8
Q

Chikungunya pathogenesis

A
  • Incubation period of 4 and 7 days
  • Fever and severe, debilitating joint pain
  • Arthralgia can last for months and disease can evolve to chronic rheumatoid arthritis
  • Neurological, cardiac and GIT problems in older patients
  • Meningoencephalitis in neonates
  • No cure, and treatment is focused on relieving the symptoms
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9
Q

Ross River Virus

A
  • (+)ssRNA, enveloped
  • Alphavirus genus, Togaviridae family
  • Aus endemic
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10
Q

Ross River Transmission

A
  • Transmission is maintained in mosquito mammal cycle involving macropods and other marsupials.
  • Rodents and horses act as amplifier hosts
  • Spread by different types of mosquitoes with Aedes vigilax most common
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11
Q

Ross River Fever

A
  • Most infections asymptomatic
  • Causes acute febrile illness for 2-5 days followed by prolonged arthralgic disease that may last for many months
  • ““Epidemic polyarthritis”
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12
Q

Barmah Forrest Virus

A
  • (+) ssRNA,enveloped
  • Alphavirus genus, Togaviridae family
  • Second most prevalent arbovirus disease in Australia
  • Clinical presentation closely mimics that of RRV
  • Arthritis is more common in RRV, rash more common in BFV infection
  • Similar to RRV, transmission is maintained in mosquito-mammalian cycle
  • Aedes vigilax
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13
Q

Flaviviruses structure

A
  • (+)ssRNA, enveloped virus
  • Assembled using three viral structural proteins, a host lipid envelope and the viral genomic RNA.
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14
Q

Three viral structural proteins of Flaviviruses

A

C, prM and E

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15
Q

E protein

A

A three-domain structure (referred to as domains E-DI, E-DII and E-DIII) tethered to the viral membrane and is antigenic determinant

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16
Q

Flavivirus replication cycle

A
  • Virions are internalized by clathrin-dependent mechanisms that usurp host factors involved in the uptake of large macromolecules
  • Viral RNA replication occurs on membranes of the host reorganized through the actions of the nonstructural proteins.
  • These virus-induced membrane structures spatially coordinate viral genomic RNA replication and virion morphogenesis, and shield replication products from host innate immune sensors.
  • Virus particles assemble at and bud into the ER and traffic out of the cell
17
Q

Flavivirus genome

A

Genomic RNA encodes a single open reading frame flanked by highly structured untranslated regions (UTR) that coordinate viral translation, replication and regulation of the innate immune response.

18
Q

Examples of flaviviruses

A
  • Yellow fever
  • Dengue
  • Japanese encephalitis
  • Murrary valley encephalitis
  • West Nile
19
Q

Different disease syndromes of flavivirus

A
  • Neurotropic disease
  • Visceral disease
  • Congenital disease
20
Q

Neurotrophic disease

A
  • Encephalitis
  • Cognitive impairment
  • Flaccid paralysis
21
Q

Congenital disease

A
  • Microcephaly
  • Placental insufficiency
22
Q

Visceral disease

A
  • Hepatitis
  • Vascular leakage
  • Haemorrhage and bleeding
  • Shock syndrome
23
Q

Dengue

A
  • (+) ssRNA, enveloped virus Genus Flavivirus, Family Flaviviridae
  • Four distinct serotypes: DENV-1 – DENV-4
  • RNA genome, exits as quasispecies and as clades or genotypes
24
Q

Peak dengue viraemia

A

Correlates with high fever and coincides with the initiation of IgM and IgG production, which promote clearance of virus infection.

25
Q

Secondary heterologous DENV infection

A

Period of viraemia is shorter, due to cross-reactive immunity, including pre-existing antibodies

26
Q

Dengue fever

A
  • Flue like illness
  • Hypovolemic shock (severe dengue)
  • Severe disease frequently occurs in the setting of secondary infection with a heterologous serotype
  • Immunity to infections with one serotype is lifelong
27
Q

Murray Valley Encephalitis Virus

A
  • (+) ssRNA, enveloped virus
  • Genus Flavivirus, Family Flaviviridae
  • Member of the JEV serogroup
  • Maintained in enzootic foci in water birds
  • Spread of MVEV outside enzootic foci is likely due to rainfall and flooding that allowed movement of infected water birds to previously arid environments
28
Q

MVEV clinical manifestations

A
  • Commonly subclinical infection with fever or headache
  • Can cause encephalitis (altered mental status, convulsions and coma)
  • 4 week incubation
29
Q

West Nile Virus

A
  • (+) ssRNA, enveloped virus
  • Genus Flavivirus, Family Flaviviridae
  • Humans horses and mammals are dead end hosts
  • Cycles between mosquitoes (culex species) and birds
30
Q

West Nile Virus clinical manifestations

A
  • Most infections asymptomatic
  • Symptoms include headache, body aches, joint pains, vomiting, diarrhoea or rash
  • Severe disease causes encephalitis
  • No vaccine or antivirals
31
Q

Bunyaviruses

A
  • Spherical, enveloped particles 90 to 100 nm in diameter
  • (-) ssRNA, segmented genome, enveloped virus
  • Comprised of only four structural proteins.
  • Genomes are divided into three negative single-stranded RNA segments, which are hidden by
    multiple copies of N.
  • Genetic reassortment can occur during infection because the RNA is segmented
32
Q

Structural proteins of bunyaviruses

A
  • Two of them are envelope
    glycoproteins (Gc and Gn),
  • The other two are internal proteins, the nucleocapsid protein or nucleoprotein (N) and the L protein (the viral RNA polymerase).
33
Q

4 genera of Bunyaviruses that are human pathogens

A
  • Orthobunyavirus
  • Nairovirus
  • Phlebovirus
  • Hantavirus
  • All but Hentaviruses are arboviruses
34
Q

Crimean Congo haemorrhagic fever virus

A
  • (-) ssRNA, segmented genome, enveloped virus
  • Genus Nairovirus, Family Bunyaviridae
  • Maintained in Hyalomma ticks
  • Transmitted to humans by close contact, tick bites, or contact with infected animals immediately after slaughter
35
Q

Crimean Congo haemorrhagic fever virus infecion

A
  • Incubation period following tickbite 1-3 days to 9days
  • Following contact with blood or tissues 5-6 days to 13 days.
  • Acute febrile illness which may be followed by abdominal pain, petechial rash and haemorrhagic phenomena
  • 40% mortality rate
36
Q

Rift Valley Fever Virus

A
  • (-) ssRNA, segmented genome, enveloped virus
  • Genus Phlebovirus, Family Bunyavirales
  • Maintained in livestock (mosquito cycle)
  • Transmitted by close contact with infected animals immediately after slaughter
37
Q

Rift Valley Fever Virus Infections

A
  • Incubation period of 2-6 days
  • Majority asymptomatic
  • Typically, patients recover within two days to one week after symptom onset.
  • Small percentage (8-10%) of people infected with RVFV develop much more severe symptoms

MICR3320 (25 decks)

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