ILC 1.13: Herpesviruses Flashcards
how are herpesviruses categorized?
α, β and γ
where do α herpesviruses establish latency?
neurons
which herpes strains are in the α group?
- HHV-1 = herpes simplex virus type 1 (HSV-1)
- HHV-2 = herpes simplex virus type 2 (HSV-2)
- HHV-3 = varicella zoster virus (VZV)
- Herpesvirus B
where do β herpesviruses establish latency?
T cells
sometimes macrophages too
which herpes strains are in the β group?
- HHV-5 = cytomegalovirus (CMV)
- HHV-6 = human herpesvirus 6
- HHV-7 = human herpesvirus 7
which herpes strains are in the γ group?
HHV-4 = EBV
what is the structure of the herpesvirus virion?
- icasahedron capsid
- linear dsDNA
- matrix proteins present
- enveloped
what is tegument?
aka matrix proteins, they just have a specific name when it comes to herpes viruses
describe the genome of the herpesvirus
linear, dsDNA with repeat sequences at the ends
this means that the virus will circularize at some point during the replication process!
the repeats will be maintained during replication process, they’re intentional
how does the herpesvirus enter a cell?
pH independent OR pH dependent manner
what mechanism does the herpesvirus use to replicate?
rolling circle mechanism
like toilet paper
what is a persistent infection?
viral infection does not result in cell death
instead there is continuous production of low titers
mechanisms leading to this situation are unknown
what is a latent infection?
involves maintenance of the viral genome without replication
so there’s a primary lytic cycle but then it just stops replicating and goes to sleep
you might not have an antibody response during this phase because no virus is being produced
latently-infected cells can be reactivated, often by stress, or during periods of impaired immunity
reactivation is characterized by new virus production
how do you know when HSV-1 is in a latent phase?
latency is characterized by the generation of untranslated mRNAs called latency-associated transcripts (LAT)
how do you know when CMV is in a latent phase?
there is no detectable RNA or protein synthesis
when herpesvirus resurfaces after a latent phase, where does it appear?
in the same spot!!
HSV-1 and HSV-2 are α-herpesviruses that go latent in neurons so usually its the innervating neuron associated with the primary infection
what are the most common clinical features of HSV?
- vesicular rashes
- oral herpes = HSV-1
- genital herpes = HSV-2
- fetal infection in utero is often fatal
most infections are symptomatic so you can physically see that someone has herpes unlike other viruses that go under-diagnosed because they don’t have as many presenting symptoms
how can you differentiate between HSV-1 and HSV-2?
they’re both α-herpesviruses
but HSV-1 is usually oral herpes = above the waistline
HSV-2 is usually genital herpes = below the waistline
what are some other clinical presentations of HSV?
- herpes pharyngitis
- eye infection
- finger infection
- skin infection
- herpes encephalitis = most common cause of fatal sporadic encephalitis cases
how do you diagnose HSV?
- distinct vesicular blisters
- Tzanck smears = scrape the bottom of a lesion and look at it under a microscope –> you’ll see balooned cells and Cowdry inclusion bodies
Cowdry inclusion bodies = intranuclear inclusions where virus is replicating
- other diagnostic methods include virus isolation/culture in cell lines, electron microscopy, immunofluorescence, and PCR
what is the pathogenesis of HSV?
initial acute infection with the virus replicating at the site; you’ll have a normal replication cycle where lots of virus is being procued
then the cell dies; lots of times with HSV there is disease associated with this
after the initial infection, the virus will infect innervating neurons and hide in the neuron = not an acute infection anymore
the virus changes its replication program so that it’s no longer replicating like it does in the epithelium and fibroblasts
then when the conditions are right, the virus will come out of the neuron and travel back up the axon and infect those same epithelial cells
how do you prevent HSV?
there is no vaccine against HSV-1 or HSV-2….
health-care workers should use latex gloves to prevent infection
condoms help, but may not always be fully protective
patients with a history of HSV infection must abstain from sexual contact while they have prodromal symptoms or lesions; the latter must be fully reepithialized
how do you treat HSV?
acyclovir
acyclovir is phosphorylated by HSV-encoded thymidine kinase and acts as a terminator of viral DNA synthesis
other options include valacyclovir, penciclovir and famciclovir
what type of herpesvirus is VZV?
alpha herpesvirus
VZV = varicella zoster virus