Varicella zoster virus as a paradigm Flashcards
what is the eclipse period
the period from virus entry until new virions are released
what is the incubation period
time from exposure until appearance of rash of specific clinical sign
what is the prodrome
when non specific symptoms appear before more specific features occurs a bit before incubation period has ended
what is the reproductive number
Average number of secondary cases arising from a single index
case in a totally susceptible population
what is the structure of the herpes virus
all look identical under EM, ds dna genome, enveloped, isocahedral capsid, images look like fried eggs
how many human herpes viruses have been identified
8
what is lytic infection
During lytic infection, host cells are
productively infected. New virions cell lysis.
what is latent infection
occurs after primary infection period where no new virions are made, latency genes may be expressed, reactivation of virus can occur going back to virion production
does the body clear primary herpes infections
no infection persists in latent state, reactivation may be clinical or sub clinical
if an individual is seropositive for antibodies to herpes are they immune
no serposistivity indicates infection not immunity, infection may be in lytic or latent phase
what drugs can control productive herpes infections
aciclovir and ganciclovir for cmv
can animals catch vzv
no humans only there is no animal reservoir
what does primary infection with varicella zoster virus cause
it causes varicella/chickenpox intially
where does VZV stay latent
it hides in dorsal root or cranial nerve ganglia
what does reactivation of VZV cause
zoster/shingles
what happens in zoster
• During reactivation virus travels down sensory
nerves and produce painful vesicles in the area
of skin served by infected ganglion
by 13 years old in uk what percent of children will have vzv/ chickenpox
90%
how does VZV incidence differ globally
people from more tropic countries get the virus later and it often present worser than in childhood
what is the incubation period of VZV
10-21 days
what is the prodrome of VZV
fever malaise pharyngitis
whats are the sgins of VZV
Itchy/painful lesions appear in crops
• Macule →papule → vesicle → pustule → crusts
• More severe in adults / Immunocompromised
what are the complications of varicella
Severe / hemorrhagic varicella • Pneumonia (adults) • Acute cerebellar ataxia (children) • Encephalitis • Secondary bacterial infection
why is indirect testing for VZV not useful
indirect looks for antibodies present, these do not present intially so to avoid a delay in treatment look directly for the virus, swab the lesions containing virus
desribe the memory immmuntiy that persists after varicella
After naturally acquired primary VZV infection:
Persistence of
– VZV-specific IgG & VZV IgA antibodies
– VZV- specific CD8 and CD4 T cells
• Adaptive T cell response needed to
prevent/control symptomatic reactivations of
endogenous VZV
