Varicella Zoster Flashcards
Describe the VZV virus
- dsDNA
- Enveloped
- Part of alpha herpesviridae family (like HSV)
What does primary VZV infection cause?
Chickenpox (varicella)
Where does VZV lie latent and why?
Dorsal root/cranial nerve ganglia - gets into nerve root from lesions in skin and travels to these areas
What does reactivation of VZV cause?
Shingles (zoster)
What happens during VZV reactivation?
- The virus travels down sensory nerves and produces painful vesicles in the area of skin served by the infected ganglion
- When it is travelling down the nerve it can’t be reached by T cell response
- More likely to get reactivation with T cell deficiency
What is the incubation period of varicella?
10-21 days
What symptoms occur in the prodrome of the the disease?
Fever, pharyngitis, malaise
Describe the lesions in varicella
- Itchy and painful
- Appear in crops
- Macule to papule to vesicle (blister) to pustule (yellow) to crusts
In what kind of patient is varicella more severe?
Adults and immunocompromised
What does more lesions indicate?
Higher viral load
How do you get the best sample?
Push the base of the lesion with the swab as there are more cells at the base of the lesion
What are possible complications of varicella?
1) Severe/haemorrhagic varicella
2) Pneumonia (adults)
3) Acute cerebellar ataxia (children)
4) Encephalitis
5) Secondary bacterial infection
When is someone with varicella no longer infectious?
When all the lesions have crusted over
When are you infectious with varicella?
From 48h before the rash until all lesions are crusted
Can you be asymptomatic with varicella?
Yes
Describe memory immunity of varicella
- After naturally acquired VZV infection there is persistence of VZV IgG and IgA as well as VZV CD8 and CD4 cells
- Adaptive T cell response is needed to prevent/control symptomatic reactivations of endogenous VZV (booster response when encounter someone with chickenpox)
What are the clinical features of zoster?
- Pain at site may precede eruption of painful vesicles
- Unilateral + 1-2 dermatomes involved (if immuno compromised might get multi-dermatomal shingles)
Why does an immunocompetent individual rarely suffer at most 2 attacks decades apart during a lifetime?
Bc shingles itself is a boost to VZV immunity so unlikely to get it soon after another one
What are three complications of zoster?
1) Involvement of eye in 50%, ophthalmic division of trigeminal nerve, indicated by lesion on top of nose (need to see ophthalmologist)
2) Post-herpetic neuralgia - chronic pain that continues after rash has cleared (weeks-years after) in same area as rash
3) Acute retinal necrosis PORN - can spread to both eyes and cause blindness
What does incidence of PHN increase with?
Age
What groups are more likely to get zoster?
Old and immunocompromised
What are the most common dermatomes involved?
1) Thoracic (50%)
2) Cranial (20%)
3) Trigeminal (14%)
4) Lumbosacral (16%)
When can children develop shingles?
- If they are exposed to chickenpox as a neonate due to maternal varicella infection
- They don’t develop a proper immune reaction or memory bc it is fought off by passive maternal antibodies instead of own immune system
What is a common presentation of shingles in children?
Dermatomal rash on leg
