Viruses Flashcards
what type of agents are viruses
sub cellular & infectious
what type of parasites are viruses
obligate intracellular parasites
as parasites, what do viruses need to do in order to replicate
need to invade other (host) cells
what size are viruses
20-300nm (small)
what do viruses depend on to independently replicate and grow to synthesise their own nucleic acid or protein
a host cell
what of the host cell do viruses take advantage of
metabolic machinery to create progeny virions
what do a broad variety of viruses contribute to
human disease
which microscope is needed to view viruses
electron
what does the basic structure of a virus consist of
a capsid surrounding a viral genome
what is the genome and capsid together referred to as
nucleocapsid
what is the capsid
a protein shell composed of repeating sub units called capsomeres
what does the capsid enclose
the nucleic acid
what is a preferred capsid morphology
icosohedral symmetry (20 equalateral triangular faces)
what is the glycoprotein which surrounds the virus cell
the capsid in addition to a plasma membrane around
what are the glycoproteins sticking out of
the plasma membrane, so virus has a membrane coat as well as a protein shell
what is the glycoprotein made out of
small protein sub units
what alternative morphologies exist of viruses
- helical nucleocapsid
- other virus families are surrounded by a lipid envelope (derived from the host cell membrane). the envelope is studded with glycosylated transmembrane proteins
what are the lipid envelopes which surround some virus families derived from
the host cell membrane
what can the viral genome be composed of
- DNA double strand
or - RNA single strand or double strand
what can viruses be classified according to
their genome type and replication strategy
baltimore classification
which groups of DNA viruses usually enter the host nucleus before they can replicate
groups: 1, 2 & 6
give example of double stranded DNA viruses
- adenovirus
- herpes virus
give an example of a single stranded DNA virus
parvovirus
give an example of a double stranded DNA reverse transcriptase (RT) virus
hepatitis B
how does the double stranded DNA reverse transcriptase virus, hepatitis B replicate
replicates through a single stranded RNA intermediate
which RNA viruses usually replicate in the cytoplasm
3, 4, 5 & 6
what can single stand RNA viruses replicate through
- either a +ve sense nucleotide sequence which can access ribosomes directly
or - -ve sense which must be transcribed into a readable +ve sense strand form before transcription
what is a -ve sense strand
the complementary base pairing of the messenger RNA sequence (sense strand) of a nucleotide
what single strand RNA viruses replicate through a DNA intermediate
HIV
what do double stranded RNA replicate via
+ve sense RNA
list the RNA viruses which infect humans
- picornavirus
- astrovirus
- calicivirus
- flavirus
- togavirus
- reovirus
- orthomyxovirus
- bunyavirus
- retrovirus
- coronavirus
- arenavirus
- filovirus
- rhabdovirus
- paramyxovirus
list the DNA viruses which infect humans
- parvovirus
- hepadnavirus
- papovavirus
- adenovirus
- iridovirus
- herpesvirus
- poxvirus
what do RNA viruses which infect humans always have in their structure
always has a bit of nucleic acid in the middle, which is protected & surrounded by a protein core called a protein capsid (protein membrane)
list the different types of respiratory viruses
- adenovirus (respiratory tract infections)
- parainfluenza virus (pharyngitis/sore throat)
- rhinovirus (tonsilitis and sinus infection)
name a type of retrovirus
HIV (AIDS)
what is the virus of warts called
papovirus
give an example of pox virus
small pox
give an example of a hepatitis virus
hepatitis A-E (liver dysfunction)
how does a retrovirus get incorporated into a cell geno
it starts off in RNA virus and contains an enzyme called reverse transcriptase which converts RNA into DNA which can get incorporated into the cell geno
list the viruses which are childhood diseases
- rubella
- rubeola (measles)
- mumps
what is the herpes virus in children known as
chicken pox
what is herpes virus in adults known as
shingles
list the different types of herpes virus
- HSV-1
- HSV-2
- CMV
- EBV
- VZV
what comes under the VZV herpes virus
- cold sores
- gladular fever
- lymphomas
- shingles
- acute CNS infections
what does the first stage of viral infection involve and what are the different strategies
entry into the cell via:
- attachement
- translocation
- genome insertion (naked virus)
- membrane fusion (enveloped virus)
- endocytosis and endosome formation (enveloped virus)
how does translocation occur, as a strategy of the virus entering into the cell
virus binds to cell membrane and remains the same
how does genome insertion (naked virus) occur, as a strategy of the virus entering into the cell
capsid merges with the cell and releases its geno inside the cell
how does membrane fusion (enveloped virus) occur, as a strategy of the virus entering into the cell
virus already has a lipid coat on the outside & blends with the lipid coat of the host cell and then passes on its capsid and nucleic acid inside the host cell
what is the viral genome transcribed to form
new virions
what does translation use
host cell machinery
during translation which uses the host cell machinery, what are the first proteins to generally be synthesised
DNA or RNA polymerases
during translation which uses the host cell machinery, where does DNA replication occur
in the nucleus
during translation which uses the host cell machinery, where does RNA replication occur
in the cytoplasm
describe the way in which DNA viruses invade a cell and cause an infection to propagate
- virus enters the cell and gets dissociated, where the capsid has dissipated and is destroyed leaving behind the viral DNA
- which is incorporated into the host cell geno
- so it goes to the nucleus and gets translocated by the nucleus and is entered into the host cell DNA which instructs cells to produce the various components of the virus
- so it will direct the synthesis of viral proteins
- so there are capsids of the viral protein coat and will direct the process of replicating DNA of the viral DNA and they become assembled into the cytoplasm of the host cell
- and through exocytosis the viral cells are dissipated and leave the cell where they go on to infect other cells
what do retroviruses e.g. HIV which are RNA viruses convert their ssRNA into
dsDNA
where can viral assembly occur within a host cell
nucleus or cytoplasm
what can viral-induced pathology be a result of
direct viral action leading to host cell death
how can damage of virus occur
due to immune response to viral antigens, where antibodies bind with the virus and stop them from invading the host cell
what do natural killer cells on host cells provide
an antiviral property
how does the T cell surveillance system mechanism work
- cytotoxic T cells can lock onto one of our body cells and have the ability o differentiate normal cells from virally infected cells
why can we have a T cell surveillance system
because we have MHC proteins which present antigens to T cells and all of our cells have class one MHC cells on the surface of proteins which function as antigen presentation, which periodically samples proteins from within its cytoplasm and shows them on the surface of the cell and then the T cytotoxic cell comes along and locks onto the MHC complex and is able to differentiate between normal proteins and viral proteins so it its a normal protein, it will leave the cell and move along, is its a virally infected cell, it can trigger the destruction of that cell through apoptosis, which is a standard mechanism that all our cells have
list the routes from which viruses can be spread
- respiratory droplets (cold/flus, inhaled)
- faecal-oral (not wash hands and then transferred)
- parenteral - sharing infected needles, can transfer HIV or hepatitis
- sexual activity
what can be established after a primary infection with some viruses
a latent infection
give an example of a latent infection
herpes virus
when a coldsore goes away, the virus does not go away.
it enters one of the sensory nerves and tracks back to the trigeminal ganglia & sits there in its latent form, to be subsequently activated, so once you acquire that infection, your stuck with it in its latent form and you keep getting secondary infections
when can you develop cold sores
when you don’t feel well
how long does acquiring HIV from the beginning to the end (aids) last
10 years
what type of symptoms are present during acute stage of HIV
flu like symptoms in first 10-16 weeks, virus is at its peak and detectable
what occurs during 2-10 years if HIV
antibody positive, no clinical symptoms, virus fallen down to base line but is still detectable because the immune system is still functioning normal and able to suppress levels of virus, px may not know they have the disease
what occurs 2-3 years after the asymptomatic stage of HIV
symptomatic
lymphadenopathy (enlarged lymph nodes), fever, weight loss
CD4+ cells go down & px is susceptible to illnesses as viral levels increase
what happens 2+ years after the asymptomatic stage of HIV
AIDS
die from opportunistic infections
what does the HIV virus only target within the body
the T helper cells = CD4+
which help orchestrate the whole of the immune system
what happens when CD4+ T helper cells are knocked out
we will have a massive immunosuppression
what is in vitro propagation in cultured cells
cells can be fixed and screened for infection
what can serological tests screen for
anti-viral antibodies
what can be used for molecular diagnosis
PCR and hybridisation techniques
what does diagnostic virology do
checks antibodies in blood
give an example of an antiviral agent
virucides e.g. detergents, chloroform uv light
what can anti viral agents target
specific components of the viral life cycle e.g.
- attachment
- penetration of virus into cell
- inhibition of replication of virus
how do most HIV drugs work
inhibition of replication of virus
what does the drug interferon do as an antiviral agent
stimulate the host immune response
what anti viral agent can increase long term protection from viruses, and how
MMR
active immunisation with subunit or live attenuated viruses
how can passive immunity be achieved
using high dose antiviral antibodies
give an example of a high dose antiviral antibody
Varicella zoster
what does chlamydia do
obligate intracellular pathogens
what category does chlamydia fall into
is its own category
what is chlamydia similar to
bacteria
how is chlamydia different to bacteria
cannot replicate on its own, must penetrate into a cell
what are the 3 species of chlamydia which causes human disease
- chlamydia trachomatis
- chlamydia pneumoniae
- chlamydia psittaci
which species of chlamydia causes, sinusitis, bronchitis and pneumonia
chlamydia pneumoniae
which species of chlamydia can also cause pneumonia
chlamydia psittaci
which species of chlamydia causes, urogenital infection, conjunctivitis and trachoma
chlamydia trachomatis
how can you diagnose chlamydia disease
by scraping off and staining the cells to detect the disease
what is the infectious agent of chlamydia
the elementary body which binds to receptors on host cells
what is chlamydia unable to synthesise
ATP
what is chlamydia responsive to
antibiotics
