Virology Flashcards
def. of virus
broad general term for any aspect of the infectious agent which includes: infectious or inactivated particle, viral nucleaic acid and protein in infected cell
def. of virion
complete intact virus particle outside of the cell
def. viroid
short stretch of circular single stranded RNA without a protein coat
what can virus be seen with
electron microscope
what is virus structre
core of nucleic acid surrounded by protein coat +/- evelope
3 different options for nucleic acids in viruses
- DNA or RNA
- single or double stranded
- linear/circular
what proteins are in viruses
- structural - capsid made of capsomeres
2. enzymes - few, differ from host cell
what is significance of virus enzymes
target for drugs
what is envelope made from
cell as it pushes out
5 different morphologies of virus
- helical/tubular - +/- envelope
- icosahedral - +/- envelope
- complex
what is enveloped cubic virus for sure
herpesviridae
4 ways to class viruses
- type and stucture of viral nucleic acid
- strategy used in replication - site
- type of symmetry of virus capsule
- presence of envelope
what are virus families
similar structural, genomic and replication properties (suffix viridae)
what are virus genera
subdivisions of families (suffix: virus)
what are genera subtypes based on
nucleotide sequences and antigen reactivities
6 DNA viruses - rest are RNA
- Hep B
- HPV
- parvovirus
- herpes
- adenovirus
- polyoma viruses
viral replications steps (7)
- adsorption (attachment)
- entry
- uncoating
- transcription
- synthesis
- assembly
- release
how do viruses attach
- random collision
- interaction between specific proteins on virus and on surface of cell
- able to only infect a limited range of cells
2 mechs. of virus entry
- endocytosis
2. fusion of envelope with cell
how do virus uncoat
cell enzymes strip capsid - no longer visible
2 things that must be synthesized
- proteins (structural and enzymes)
2. nucleic acids - new virus genome
where do DNA virus do their replications
- DNA in nucleus
- protein in cytoplasm
- move proteins into nucleus for packaging
2 types of RNA viruses and how they replicate
+sense - actas a mRNA and can make proteins immediatelly
-sense - must first make a +sense using viral enzymes and then copy
how do retroviruses work
contain reverse transcriptase
- +sense RNA > cDNA > integrated directly into the host chromosome
- virus doens’t need to do any work
2 ways of release
- bud out
2. rupture cell
2 ways virus may cause damage
- directly
2. through host reactions to the virus
2 factors that affect the outcome of viral infections
- host’s defences
2. virulence factors
4 possible outcomes of a virus-host cell interaction
- cell death - lytic
- cell transformation - cancer or malignancy
- latent infection - may reactivate any time to cause disease, may have continuous or intermittent shedding
- cell fusion to form nucleated cells - HIV
5 possible ways viruses evade the immune system
- antigenic variation - keep switching
- encode receptors for inflammatory cytokines - shutting down imune system
- reduce expression of MHC-class 1 - reducing ability of T cells to kill
- direct cell to cell propagation
- attenuation
3 types of persistent viral infections (some overlap)
- chronic carrier - chronic illness due to continuous shedding
- latent infection - may pop back up and may shed
- slow virus infections - due to prolonged incubation periods
2 routes of viral transmission
- horizontal - person to person
2. vertical - mother to fetus
when can transmission occur
- with or without disease
- during asymptomatic shedding
- during incubation period
what are some epidemiological aspects that change viral outcomes
- mode of tranmission
- age
- gender
- ethnicity
- travel Hx
- occupation
- season
- medical conditions
what is incubation time
time from infection to dev. of Sx
2 short incubation virus (1-2 days)
GI and resp viruses
3 medium incubation viruses (1-3 weeks)
- MMR
- VZV, HSV
- enteroviruses, polio
4 long incubation viruses (months)
heps, HIV, EBV, rabies
some non-specific host defences
- skin
- rest tract, cilia, mucous
- GI - acid, lymphoid
- GU- flow
tears - phago
- interferons
what does humoral do
- Ig
- neutralize viruses
- elimination of viruses
3 main Igs in virus infections
IgM - early - 1week to 6 months
IgG - months to years, responsible for immunity
IgA - dimer of 2 Igs, body secretions, mainly for GI
what does cellular defense do
- elim of virus infected cells
- most important defence
6 cell mediated types and functions
Th - stim cytotoxic response and activate B cells
Ts - control and reg. response by supressing Th
Tc - cytotoxic - min cells to kill virus infected cells
Td - delayed hypersentitivity cell - release macrophage activating factor
NK - direct killing of infected cells
interleukins - modulate immune response
5 times rapid and accurate diagnosis is important
- tranplant
- HIV
- effective chemo
- epidemiology
- transplant safety
3 methods to diagnose viruses
- isolation (culture)
- direct detection
- serology (AB/antigen)
3 methods of culture
- tissue culture
- chick embryo
- animal innoculation
how must viruses be samples
quickly and in a cool special medium
2 adv. of cuture
- definitive
2. obtain isolate for further tests
3 disadv. to culture
- not all viruses cultruable
- may take long time
- biohazard
how is direct detections done (3)
- look at the sample with electron microscope
- look for monoclonal ABs against
- PCR for viral DNA/RNA
what is serology tests
look for ABs against
4 ways to diagnose in serology
- IgM ABs
- four fold rise in AB titre
- seroconversion
- very high single AB titre (unreliable)
