Varicella Zoster Virus Flashcards
What is chickenpox?
Varicella zoster virus
Belong to the family of Alpha herpes viruses
When does chickenpox normally present?
Normally a mild illness of childhood
What percentage of UK-raised adults are immune to chickenpox?
> 90%
What is the genome of varicella zoster virus?
ds DNA genome
How many base pairs does the genome of the varicella zoster contain?
130 000 base pairs
What happens during primary infection of chickenpox?
Viral replication in skin causes lesions
This presents as chickenpox
Immune control regulates this
Retrograde spread in sensory neurons
Latency is established in the ganglion
Where is latency established?
In the ganglion
What happens during reactivation of the varicella zoster virus?
Reaction from latency induced by unknown factors
Anterograde spread
Viral replication in skin causes lesions to develop and presents as shingles
What does reaction of varicella zoster present as?
Shingles
To who are herpesviruses problematic?
In immunocompromised individuals
Examples of immunocompromised individuals
HIV
Transplantation
Zoster lesions are usually limited to a single dermatome
TRUE or FALSE
TRUE
Area innervated by sensory neuron that contains latent form of the virus
Which percentage of chicken pox patients develop Zoster?
25-35%
What factor increase the incidence and severity of Zoster?
Age
Immune senescence
Chickenpox is a special risk to pregnant women, foetus and neonates
TRUE or FALSE
TRUE
Risk of fatal varicella is five times higher in pregnant women
During which time of the pregancy is material infection most risky to the foetus/neonate?
First 20 weeks: Congenital varicella syndrome (1-2% pregnancies)
Second and third trimesters: Neonatal Zoster
A week before to a week after delivery: Severe/fatal neonatal disease
Is chickenpox contagious?
Yes, highly contagious
Not determined what the main mode of transmission for the virus is
What is the chance of getting chickenpox through household contact?
100%
What is the first step to do if a mother presents to a neonatal clinic with a child sick with chickenpox?
Urgent look back at clinic list for possible contacts
What characterises people who have had contact with the child?
Face-to-face contact
15 minutes in the same room
Two hours before/after the woman’s appointment
When we have identified the women at risk of exposure, what are the next steps?
Retrieve stored sera
Taken for routine screening tests done in pregnant women
What is a mother has Hepatitis B?
Vaccine and Ig for baby
Potentially fatal to the embryo
What is a mother has Syphilis?
Antibiotics for mum
And baby if needed
Potentially fatal to the embryo
What is a mother has HIV?
ART for mum
No breastfeeding
1 month AZT for baby
Potentially fatal to the embryo
What test would you do to see if someone is immune to VZV?
Test for VZV IG via colorimetry/fluorescent substrate
What does the presence of VZV IgG in serum indicate?
Marker of prior infection
Indicates protective immunity
What should be prescribed to pregnant women who are VZV IgG negative and exposed to the virus?
VZIG
Varicella Zoster ImmunoGlobulin
What is VZIG made of?
Pooled plasma from non UK donors with high titre of anti VZV IgG
Do you have to present with chickenpox to have been exposed to the virus?
No
11% of children aged 1 to 5 years,
37% aged 6 to 16 years
89% of adults
With a negative history of chickenpox are VZV IgG positive
What is the aim of VZIG?
Reduce severity of maternal disease
Reduce of risk of foetal infection
When is VZIG given?
Infants whose mothers develop chickenpox in the period seven days before to seven days after delivery
VZV antibody-negative infants exposed to chickenpox or zoster in the first 7 days of life
What is another cause, other than shingles, of vesicular rashes?
HSV
What is a way to distinguish between HSV and VZV?
PCR
What happens when a patient in a transplant ward develops shingles?
Isolated
Treated with acyclovir
What happens to the patients in the transplant ward exposed to the patient with shingles?
Test for VZV IgG
IgG negatives: give VZIG and isolate
What type of vaccine is the chickenpox vaccine?
Live attenuated
To who is the chickenpox vaccine recommended for?
Healthcare workers
Regular/ close contacts of person at high risk from VZV
Why has the UK opted out of making chickenpox vaccine widespread?
Exposure to varicella boosts immunity to herpes-zoster
Highly protective
If remove the varicella = less protected against shingles
What has recently happened in the incidence of zoster?
Incidence of zoster is increasing
No change to rate after vaccination programme started
So vaccine is useless in protecting against shingles
What is the current vaccine used to protect against Zoster?
Zostavax
When is Zostavax taken?
Adults aged 70 years
Catch-up for adults aged 78 and 79
What is a vaccine that is currently being investigated and predicted to have better results than the Zostavax vaccine?
Herpes Zoster Subunit vaccine
What is tested to reveal someone’s history to exposure to VZV?
Antibody
ELISA
What is tested to reveal current infection of VZV?
DNA/antigen
PCR
What is the benefit of the virus being in latent stage?
Allows it to survive months immune response
Can wait for another host and reactivate
Why does the virus become latent in nerve ganglia?
No tissue turnover in neurons
How does the virus exist during the latent stage?
Sits as an episomal DNA molecule
Where are rashes originating from shingles occur most commonly?
In the waist
Why were post-mortem examinations of nerves to look at latent stage of virus ineffective?
Death is physiologically stressful
Would reactivate the virus
What technique was used to identify genes responsible for latency?
RNA transcriptome
