Microbiology Flashcards
what is a virion?
an infectious virus particle
what is a protomer?
identical protein subunit making up the capsid
what shapes can a capsid be?
icosahedral, helical or complex
name 4 viruses of icosahedral symmetry
adenovirus, papillomavirus, parvovirus, herpesvirus
name 2 viruses of helical symmetry
rhabdovirus, parainfluenza virus
name a virus of complex symmetry
poxvirus
name a non-enveloped DNA virus
canine parvovirus
name an enveloped DNA virus
feline herpesvirus
name a non enveloped RNA virus
foot & mouth disease virus
name an enveloped RNA virus
influenza virus
t/f
viral genome can be both DNA or RNA
false. can only be one or the other
where do DNA viruses replicate?
most in nucleus
where do RNA viruses replicate
most in cytoplasm
are DNA or RNA viruses more prone to mutation?
RNA viruses
are DNA or RNA viruses stable?
DNA viruses
t/f
envelopes derived from viral cell?
false. derived from host cell
are enveloped or non-enveloped viruses stable?
non-enveloped
t/f
enveloped viruses usually easily inactivated by disinfectants
true
what is mutation?
structural alteration in nucleic acid
mutation has important effects on…
- virulence of virus
- host range of virus
point mutation
single nucleotide substitutions
viral recombination
exchange or transfer of genetic material between diff but closely related viruses infecting same cell
antigenic DRIFT
gradual accumulation of point mutations (common)
antigenic SHIFT
acquisition of new gene from another virus due to recombination or reassortment (rare)
In influenza virus, what allows it to attach and to where?
Hemagglutinin, attaches to respiratory epithelium
when did the spanish influenza arise?
1918
spanish influenza aka…
H1N1 virus
how was H1N1 passed to humans
bird-to-human transmission
what are the types of virus-cell interactions?
- Lytic infection
- Persistent infection
What are types of persistent infection?
- productive
- latent
- non-productive transforming
example of lytic infections
- canine parvovirus
- foot and mouth disease virus
examples of persistent productive infections
- rabies
- foot and mouth disease
examples of persistent latent infections
- herpes virus
- retrovirus
example of non-productive transforming infections
equine sarcoids
types of viral effect on cell morphology
- cytopathic
- inclusion bodies
- alterations in cell membrane
- formation of syncytia
- haemadosorption
describe cytopathic effect
- seen in vitro
- seen in cell monocultures infected with virus
- nature of CPE can be diagnostic
describe inclusion bodies
morphological changes seen in cells infected with certain viruses
all viral infections produce inclusion bodies. t/f?
false.
give some examples of inclusion bodies
- masses of viral nucleocapsids (e.g. rabies)
- masses of viral proteins and nucleic acid (e.g. pox)
- crystalline aggregates of virions
- degenerate nuclear DNA (e.g. herpes)
give examples of alterations to cell membranes
- increase in permeability
- altered ion exchange/membrane potential
- proliferation/rearrangement of membrane
- insertion of viral glycoproteins
what is syncytia?
viral proteins inserted into plasma membrane of cell may lead to fusion of between neighbouring cells (e.g. herpes, coronavirus)
what is haemadosorption?
adherence of RBCs to other cells or particles
name ways viruses damage cells
- cell lysis
- inhibit acid synthesis
- inhibit protein synthesis
- cytopathic effects
- cytolysis
how can viral interference occur?
- superinfection exclusion
- interferon mediated interference
what are cytokines that are produced rapidly (but transiently) in response to viral infection?
interferons
what is the paracrine effect?
interferons released by infected cell and binding to receptors on neighbouring cells
what are some routes of viral entry?
- respiratory system
- alimentary system
- skin
- urogenital tract
- conjunctiva
what is the most common route of viral entry
respiratory system
how do particles enter respiratory system?
impaction - large - nasopharynx
sedimentation - medium - small airways
diffusion - small - alveoli
where are sites of defence in respiratory system?
- nasal passages
- nasopharynx
- larynx
- lower respiratory tract
where are cough receptors located?
larynx
where is the mucociliary escalator?
lower respiratory tract
where are turbinate bones?
nasal passages
where are lymphoid nodules in submucosa?
nasopharynx
what is the 2nd most common route of viral entry?
alimentary system
what are some defences of the alimentary system?
perstalsis, mucous, bile, proteases, gastric acid, secretory IgA, tight junctions, lymphoid tissue (peyers patches), constant cell turnover
what are some barrier disruptions to skin defences?
- cuts, abrasions, trauma
- biting arthropods
- animal bites
- latrogenic
where would defence mechanisms of tear production and mechanical ‘wiping’ occur?
conjunctiva
what are some defence mechanisms of the urogenital tract?
- urinary flushing
- anatomical barriers
- low pH
- secretory IgA
how can viruses spread from site on entry?
- apical release
- basolateral release
what type of directional spreading moves to contagious surfaces?
apical release
what is basolateral release?
directional shedding favouring internal dissemination
once in sub-epithelial tissues, virus disseminates via…
- lymphatics
- bloodstream
- nerves
in haematogenous spread, how can virions be transported through the blood?
- free virions in plasma
- absorbed to, or within blood cells
what is neural spread?
viral spread through peripheral nerves
retrograde (centripetal) transport
allows access to CNS
anterograde (centrifugal) transport
allows access to peripheral tissue
what is viraemia?
presence of infectious virus in the blood
what are the 3 requirements for successful infection?
- sufficient viral particles present at site of infection
- cells at site of infection susceptible and permissible
- host defences inactive or absent
how do dogs get distemper?
- transmission from recently infected animal or fresh formites
- virus enters host via aerosol droplets that contact upper respiratory tract epithelium
- viral replication within 24hrs in local tissue macrophages then spreads via these cells to local lymphoid tissue
- widespread viraemia and viral proliferation within lymphoid, acute fever and leukopaenia
- viral invasion of epithelial tissue and CNS depending on dogs humoral & cell mediated immunity and viral virulence
what is viral tropism?
ability of virus to selectively infect particular cell types
what is enterotropic?
virus replicates in cells of GIT
what is it called when virus replicates in cells of nervous system?
neurotropic
what are determinants of tissue tropism?
- accessibility
- susceptibility
- permissiveness
- immune response
viruses passed in faeces generally more resistant to environmental inactivation. true/false?
true
what are some possible outcomes of foetal infection?
- abortion/stillbirth
- foetal malformation
- foetal tolerance
- recovery with no adverse effects
with BVDV, what happens if infection occurs 80-125 days?
- defects in brain and eye tissues
- surviving calves remain infected for life
- become immune tolerant of virus
- later die of mucosal disease from viral mutation
with BVDV, when would foetal death and resorption occur?
<80days gestation
with BVDV, what is the 125 day gestation threshold significance?
immune system fully developed in foetus by 125 days
what are patterns of infection a result of?
interplay between characteristics of viral lifecycle and host immune response
acute infection is…
brief, self-limiting infection
chronic infection is…
long-lasting, from months to life
latent infection is…
resting/hiding, viral recrudescence
slow infection is…
maybe long preclinical phase, can infect others in this time
what viruses cause epithelial damage leading to secondary bacterial infections?
- canine parvovirus - septicemia
- foot & mouth - bacterial infection
what viruses cause immune damage leading to secondary infection?
- FIV - infecting lymphocytes and monocytes - reduced cell mediated immunity
- measles cause immunosuppression
what is immunopathology
damage caused by host immune response
what is a result of immunopathology?
hypersensitivity reactions
what is an example of a virus that causes immunopatholgy?
feline infectious peritonitis (FIP)
what happens when immune system recognises host proteins as foreign?
autoimmune disease
what can cause autoimmune disease?
- molecular mimicry
- revealing previously hidden antigens
- incorporation of host proteins in virions
- persistent infection
what is viral oncogenesis?
viral infection leading to tumour production
