viral infections Flashcards
(43 cards)
what are the 6 stages in general virology replication
- attachment (between virus and host cell receptors)
- cell entry (viral ‘core’ carrying nucleic acid and proteins enter )
- interaction with host cells - virus uses cell materials eg. enzymes, for their replication and to subvert host cell defence mechanism
- replication within host cell to produce structural proteins, a viral genome and other nonstructural proteins eg. enzymes
- assembly of new virions
- release - bursts out of cells, or leaves via exocytosis, or leaks by budding. causes host cell death
which antibodies are involved in the humoral response to a virus ?
IgG,A,M response
IgA blocks attachment
complement factors are also involved
what cell can kill virus particles and infected cells and is a key part of the cell mediated response to viruses?
Cytotoxic T helper cells
what is meant by viral infection?
The process by which viruses evade the immune system and Interfere with specific or nonspecific defence
They do this by mutation
define antigenic drift
Antigenic drift of viruses:
spontaneous mutations, occur gradually giving minor changes in hemagglutinin and neuraminidase.
causing change in their antigens
define antigenic shift
Antigenic shift of viruses:
sudden emergence of new subtype different to that of preceding virus.
sudden change in coat antigens
out of antigenic drift and shift, which is responsible for epidemics and pandemics ?
Drift – epidemics
Shift – pandemics
give the definition/ criteria of a virus
An infectious, obligate intracellular parasite compromising genetic materia (DNA or RNA) surrounded by a protein coat and/or membrane.
They all have a receptor binding protein to ‘dock’ to cells.
what is the name of a virus that isn’t inside an infected cell
a virion
describe the structure of a virion, what does it consist of ?
the nucleocapsid
- Genetic material (DNA or RNA)
- Protein coat (capsid)
can be enveloped or non-enveloped
- envelope= lipid coat derived from plasma membrane of the host cell
contains no membranes or walls, no cell organelles, no metabolites,
very small
name 3 different shapes a nucelopcapsid can be
helical or icosahedral or complex
can a virus survive outside a host ?
depends in type of virus and environment
eg. can’t survive in UV light
a bacterium can contain both DNA and RNA . is this true also for viruses?
no
have only 1 type of nucleic acid
would you describe viruses as living?
they cannot feed or respire
they cannot reproduce by themselves
therefore considered non-living
give ways that viruses cause disease and damage
- direct destruction of host cells
- modify host ells
- cause over-reactivity of host immune response
- cell proliferation
- evades intracellular and extracellular defences
give 2 ways that viruses evade the hosts extraceullar defence system
- latency - virus is non detectable but then can reactivate at a time of low immune control
- direct cell to cell spread - avoids immune system
give 2 ways that viruses evade the hosts intracellular defence system
- antigenic variability
- prevention of host cell apoptosis
- down regulation fo interferons and other defence proteins
what are the 2 main approaches to diagnosis of viral infection ?
- direct detection of the virus
- indirect detection of the immune response to the virus, using SEROLOGY
list some methods of direct viral detection that are now considered outdated (timely,efffort)
electron microscopy
CPE - culture viruses for 4 weeks and look at effect virus has on the cells ie. detection of a cytopathic effect
what is the preferred methods of direct viral detection
NAATs (nucleic acid amplification tests)
- identify viruses by looking for the presence of viral nucleic acid in a tissue sample, blood sample or a swab.
- most common NAAT is the PCR (polymerase chain reaction)
describe how a PCR works
- special enzymes ‘unzip’ chains of DNA or RNA
- they then make complimentary copies of the original DNA/RNA by using nucleoside bases as substrate to double the number of copies of the original.
- By repeating this process many times, logarithmic increases in the copies of RNA/DNA are created.
- The nucleoside substrate bases are each specially tagged with a fluorescent molecule which only fluoresces when bound in a chain of other bases.
5.Thus, the creation of the new DNA/RNA can be detected and quantified by measuring increases in fluorescence.
advantages to PCR
very sensitive and quick
diadvantages to PCR
- vulnerable to laboratory contamination of a sample and might give a false positive result
- an only detect nucleic material complimentary to the primer sequences used to initiate it - so you need to know the DNA/RNA sequence of the virus before complimentary primers can be designed and used. It is not possible to detect a virus via PCR unless you suspect it in the first place and use the relevant primers.
Difficult for new viruses!
indirect detection of a virus via serology
how does this work?
study the antibody responses in the serum with the virus in
