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
what are the key clincal features of zoster
reactivation of VZV which has been dormant. affects specific dermatome of which the virus was latent in it’s corresponding ganglia. Ophthalmic division of trigeminal nerve →
involvement of eye in 50% can effect eyes.
Immunocompetent less likely to suffer attacks,
strikes elderly more as immune system weakens
unilateral presentation of rash
what clinical issue can zoster cause in the eyes
Acute retinal necrosis
describe horizontal transmission of VZV
varicella spread by respiratory route, skin lesions are infectious until they crust over
describe vertical transmission of vzv
Vertical
• Congenital infection of foetus in utero
• Perinatal infection causing neonatal varicella
why is Maternal varicella occurring within 7 days before or 7
days after delivery
because mother does not have any antibodies produced to give to the baby so the baby has no protection
does maternal shingles damage foetus
no it does not, varicella is also unlikely to cause severe defects to foetus
how do you determine an individual susceptibility to VZV
find out if they have had shingles or chicken pox, check their vzv specific igg status
when should passive immunisation be used to treat individual who has been exposed to VZV
Passive immunisation with VZIG is indicated for
susceptible individuals at risk of severe VZV
infection following a significant exposure incident
• Pregnant
• Immunosuppressed
• Neonate of seronegative mother
using vzv immunglobin is one form of post exposure prophylaxis what is another method
you can use aciclovir or varivax vaccine
how do you diagnose herpes simplex virus or VZV in skin lesions during primary or reactivated infection
electron microscopy, immunofluorescence, tissue culture, NAAT PCR
when would you not use anti viral therpay for VZV
in childhood varicella that is uncomplicated
what does management of zoster involve esp if eyes effected
antivirals are recommended, ophthalmic assessment mandatory
discuss the vaccine for varicella
live attenuated vaccine, 2 dose schedule, reccomended in uk for susceptable healthcare workers and carers of immunocompromised patients, not 100 per cent effective but protects against severe primary vzv infection
discuss zoster virus who does it help
No major safety concerns, but contraindicated in significant
immune deficiency. protects against shingles especially in ederley
