Unit 4 part 6: Viruses: replication and effects of viral infections Flashcards
viral replication strategies can depend on what 4 thiings
their viral genomic nucleic acids
capsid
envelope
symmetry
what are the 6 major steps in a viral replication cycle
attachment aka adsorption penetration uncoating biosynthesis assembly release
what happens in the uncoating phase
capsid is made protein coat and the virus removes the protein coat and injects nucleic acid into the cell
what happens during biosyntheis
virus hijacks the inside machinery to make their own copies, host cell is hijaked by the virus
what happens during assembly
need to be assembled into the virus
how do naked viruses attach
through interactions between their capsid proteins and the host cell membrane receptors
how does the rhinovirus attach to a host cell since it is a naked virus
intracellular adhesions between the molecule ICAM-1 which is involved in the inflammatory and immune response
virus uses ICAM-1 as a key to get into the cell
rhinovirus binds to ICAM-1 receptors
what virus is responsible for 50% of common cold cases
rhinovirus
what can prevent the rhinovirus from attaching to ICAM-1
antibodies can bind to the surface of the rhinovirus
how do enveloped viruses attach to the host cell
use glycoprotein spikes allow the viurs to attach to the host cell surface receptors
how does HIV attach in humans
glycoprotien spikes (gp 120) on HIV attaches to CCR5 (co-receptors) on T helper cells in humans
what is CCR5 also known as
CD195
what is What kind of receptor is CCR5
chemokine - direct traffic to cellular infection so leukocytes know where the infection is
if someone lacks what receptor they are immune to HIV
CCR5
- but cannot able to direct leukocytes
what are two ways a virus can penetrate a cell
fusion between the viral envelope and the host cell membrane
endocytosis (receptor mediated) or engulfment into a vesicle
what occurs in the uncoating process
release of viral nucleic acid (from the protein coat, i.e. capsid) inside the cell
what occurs in the biosynthesis stage
synthesis of new viral nucleic acids and proteins (lots of variations!)
replication of viral genome
mRNA synthesis (transcription)
production of viral proteins (e.g. capsomers)
what do the events of biosynthesis to a varying degree depend upon
certain host-derived & virus-specific replication enzymes
what is one of the most important active and important steps in viral replication
biosynthesis
how many copies of a virus can an infected cell create in a single cycle
tens of thosands
what occurs during the viral assembly stage
newly synthesized viral genome and other components (e.g. enzymes) are incorperated into the capsid forming the nucleocapsid
the new virons from naked viruses in the assembly stage are said to be what?
mature (i.e they are complete and infectious)
- non naked viruses are not complete as they have to grab their coat on the way out
what is the final step in the viral replication cycle
release of mature viruses
how are naked viruses released
mature viruses accumulate in the cell eventually leading to cell death and are released by cell lysis (lytic infection)
how are eneveloped viruses released
nucelocapsid “buds” through the cell membrane
picks up phospholipids to produce a mature virus with the envelope (budding/exocytosis)
what leads to showing S & S in a viral infection
immune system recognizes abnormal cells
cells are destroyed
tissue damage due to inflammation and immune responses
how do antivirals work
drugs affect specific steps of the replication cycle
are their broad spectrum anti-virals
no, because viruses have very diverse multiplication strategies.
i.e. drug only works against a single type of virus but not others
vaccines existing and new for viruses are developed to target what stage of the virus replication cycle
attachment step
immunized persons make antibodies that block viral attachment to host cells (virus neutralization) to prevent infection
what are 4 possibel effects of viral infections on host cells
cytopathic effects (structural changes in a host cell) cell death (e.g. lytic infection) persistent infection transformation into tumor cells (malignancy)
what are the two types of persistent infection
chronic infection
latent infection
how are cytopathic effects (CPE) seen
under the microscope - can be useful in aiding diagnosis
what are inclusion bodies
vacuoles in teh cytoplasm and/or nucleus of infected cells
filled with new viruses and viral components
what is an example of an inclusion body
negri bodies
inclusion bodies seen in infected nerve cells caused by rabies virus’s
what are the two common types of CPE’s seen
inclusion body
giant cell or syncytium
what is a giant cell or syncytium
infected cells fuse with neighbouring cells forming a syncytium to facilitate their spread
what does a synctium look like
multi-nucleated giant cell
what are two examples of syncytium
RSV
CMV
what is RSV
syncytium called respiratory syncytial virus
common cause of bronchiolitis, bronchitis, pneumonia, otitis media,& febrile URI amoung young canadian children
what is CMV
synctium called cytomegalovirus
herpesvirus - leading cause of morbiditiy and mortality amoung organ-transplant patients
polio virus causes what type of infection
lytic
what does the polio virus cause to happen
destroys nerve cells known as motor neurons
3 characterisitcs of polio
nerve cells cannot be regenerated
affected muscles no longer function
irreveresible & extensive paralysis involving the trunk, muscles of the chest and abdomen, resulting possibly in quadriplegia and death
what happens in chronic infection
mature infectious viruses are produced and can be detected in the body at all times
e.g. hep c infection (asymptomatic)
what occurs in latent infection
viruses “hide” inside a specific body site –> virus NOT detected/shed in body fuluids at all times
what are examples of a latent infection
vacirella zoster virus (VZV or chickenpox) and herpes simplex (HSV) infection,
where do causative virus remain in a latent infection
inside the trigeminal nerve ganglia (not contagious) until reactivation
in a latent infection what can we still look for
viral genome
do latent infections evoke the immune response
no
how are viral genomes carried during latency
extrachromosomally e.g. herpes or HSV
may integrate into the host cell chromosome as proviruses or proviral DNAs
what is an example of a latent infectin that ay integrateinto the host cell chormosome as proviruses or proviral DNA
epstein-barr virus (EBV) or HIV
HIV has features of both _____ and _____ infections
chronic
latent
what 5 things can reactivate latent infections
immunosuprpression aging malnutrition stress exposure to UV light or sunlight
the reactivation of HSV infection can lead ot appearance of what
new blisters or asymptomatic viral shedding
is asymptomatic viral shedding (ASV) congatious
yes
babies born to parents with HSV have what
born with lesions that look like cigarette burns all over their face
c section done to avoid this
what is transformation
normal cells infected with viruses can be transformed into tumor cells
normal cells can be turned into tumor cells by the activation of what
viral oncogenes
what is an example of a viral oncogene virus
HPV
what can transoformation due to host cell chromosomes
integration of viral genes or genome into host cell chromosome
what virus causes burkitt lymphoma and infectious mononucleosis
EBV
hepatitis B virus causes what type of cancers
hapatocellular carcinoa (liver cancer)
how many cases of cancer does HBV (hepativits B virus) account for
60%
what cancer does the epstein-barr virus aka human herpes virus 4 cause
burkitt lymphoma nd nasopharyngeal carcinoma
what cancer does herpes simplex 2 aka human herpes virus 2 cause
cervical cancer
genital herpes
hepatitis C causes
HCC
