Varicella zoster virus as a paradigm

Question 1

what is the eclipse period

Answer 1

the period from virus entry until new virions are released

Question 2

what is the incubation period

Answer 2

time from exposure until appearance of rash of specific clinical sign

Question 3

what is the prodrome

Answer 3

when non specific symptoms appear before more specific features occurs a bit before incubation period has ended

Question 4

what is the reproductive number

Answer 4

Average number of secondary cases arising from a single index
case in a totally susceptible population

Question 5

what is the structure of the herpes virus

Answer 5

all look identical under EM, ds dna genome, enveloped, isocahedral capsid, images look like fried eggs

Question 6

how many human herpes viruses have been identified

Answer 6

8

Question 7

what is lytic infection

Answer 7

During lytic infection, host cells are

productively infected. New virions cell lysis.

Question 8

what is latent infection

Answer 8

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

Question 9

does the body clear primary herpes infections

Answer 9

no infection persists in latent state, reactivation may be clinical or sub clinical

Question 10

if an individual is seropositive for antibodies to herpes are they immune

Answer 10

no serposistivity indicates infection not immunity, infection may be in lytic or latent phase

Question 11

what drugs can control productive herpes infections

Answer 11

aciclovir and ganciclovir for cmv

Question 12

can animals catch vzv

Answer 12

no humans only there is no animal reservoir

Question 13

what does primary infection with varicella zoster virus cause

Answer 13

it causes varicella/chickenpox intially

Question 14

where does VZV stay latent

Answer 14

it hides in dorsal root or cranial nerve ganglia

Question 15

what does reactivation of VZV cause

Answer 15

zoster/shingles

Question 16

what happens in zoster

Answer 16

• During reactivation virus travels down sensory
nerves and produce painful vesicles in the area
of skin served by infected ganglion

Question 17

by 13 years old in uk what percent of children will have vzv/ chickenpox

Answer 17

90%

Question 18

how does VZV incidence differ globally

Answer 18

people from more tropic countries get the virus later and it often present worser than in childhood

Question 19

what is the incubation period of VZV

Answer 19

10-21 days

Question 20

what is the prodrome of VZV

Answer 20

fever malaise pharyngitis

Question 21

whats are the sgins of VZV

Answer 21

Itchy/painful lesions appear in crops
• Macule →papule → vesicle → pustule → crusts
• More severe in adults / Immunocompromised

Question 22

what are the complications of varicella

Answer 22

Severe / hemorrhagic varicella
• Pneumonia (adults)
• Acute cerebellar ataxia (children)
• Encephalitis
• Secondary bacterial infection

Question 23

why is indirect testing for VZV not useful

Answer 23

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

Question 24

desribe the memory immmuntiy that persists after varicella

Answer 24

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

Question 25

what are the key clincal features of zoster

Answer 25

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

Question 26

what clinical issue can zoster cause in the eyes

Answer 26

Acute retinal necrosis

Question 27

describe horizontal transmission of VZV

Answer 27

varicella spread by respiratory route, skin lesions are infectious until they crust over

Question 28

describe vertical transmission of vzv

Answer 28

Vertical
• Congenital infection of foetus in utero
• Perinatal infection causing neonatal varicella

Question 29

why is Maternal varicella occurring within 7 days before or 7
days after delivery

Answer 29

because mother does not have any antibodies produced to give to the baby so the baby has no protection

Question 30

does maternal shingles damage foetus

Answer 30

no it does not, varicella is also unlikely to cause severe defects to foetus

Question 31

how do you determine an individual susceptibility to VZV

Answer 31

find out if they have had shingles or chicken pox, check their vzv specific igg status

Question 32

when should passive immunisation be used to treat individual who has been exposed to VZV

Answer 32

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

Question 33

using vzv immunglobin is one form of post exposure prophylaxis what is another method

Answer 33

you can use aciclovir or varivax vaccine

Question 34

how do you diagnose herpes simplex virus or VZV in skin lesions during primary or reactivated infection

Answer 34

electron microscopy, immunofluorescence, tissue culture, NAAT PCR

Question 35

when would you not use anti viral therpay for VZV

Answer 35

in childhood varicella that is uncomplicated

Question 36

what does management of zoster involve esp if eyes effected

Answer 36

antivirals are recommended, ophthalmic assessment mandatory

Question 37

discuss the vaccine for varicella

Answer 37

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

Question 38

discuss zoster virus who does it help

Answer 38

No major safety concerns, but contraindicated in significant

immune deficiency. protects against shingles especially in ederley