Infectious Disease: Chicken Pox

Question 1

Defintion

Answer 1

Varicella-zoster virus (VZV) is a herpes virus responsible for chicken pox (primary infection in non-immune hosts) and shingles (following reactivation of latent infection)

Chickenpox predominantly occurs in childhood and it is spread via airborne droplets and also from direct skin contact with vesicular fluid.

Chickenpox is characterised by an itchy, vesicular rash. Chicken pox can be much more severe in adults and pregnant women

Question 2

Epidemiology

Answer 2

Age: most common < 10 years of age
Formal day-care attendance
Large household size

Question 3

Pathophysiology

Answer 3

Intubation period 15-21 days
Primary VZV infection, in the form of chickenpox, starts with viral replication in respiratory regional lymph nodes 2-6 days the virus then enters the circulation for primary viraemia. The virus then enters the reticuloendothelial system and another bout of viremia occurs in 10-12 days, leading to the development of the chickenpox rash.
Once the primary VZV infection has resolved, the virus is thought to spread to and remain latent within dorsal ganglion cells of sensory nerves .
Chickenpox only occurs once due to the antibodies against VZV which persist for life conferring immunity.

Question 4

Shingles defintion

Answer 4

Shingles , also known as herpes zoster, is caused by reactivation of VZV and affects an individual nerve, or cranial nerve (e.g. Ramsay-Hunt Syndrome) and the skin surface served by it (dermatome).

Question 5

Signs and symptoms

Answer 5

Incubation period (2 weeks)
Prodromal phase (1-2 days)
- most infective period
- fatigue
- fever
- malaise
Exanthem phase (5-6 days)
- vesicular rash starts on the trunk/face and spreads
- the rash initially begins as a macula before evolving -> papule -> vesicles and pustules
- the vesicle and pustules then erupt and crust within 5 days of onset
- healed lesions may appear hypo or hyperpigmented for several months.

Question 6

Diagnosis

Answer 6

Clinical

Question 7

Management

Answer 7

Usually self-limiting however a low threshold for hospital admission should be considered.

Children and adults:
- conservative measures = paracetamol for pain, topical calamine lotion, chlorphenamine to treat pruritus.
- NSAIDS should be avoided
- children should be kept from school or nursery until the vesicles have crushed over
- Aciclovir: if < 13 years old, can be considered in patients who present within 24 hours of rash onset particularly severe cases or those at risk of complications

Question 8

Complications

Answer 8

• Superinfection: impetigo , cellulitis , and necrotizing fasciitis. Bacterial superinfection can lead to scarring
• Severe disseminated chickenpox : seen in immunocompromised patients
• Neurological complications: encephalitis , cerebellar ataxia, Reye’s syndrome
• Pneumonia: smokers and pregnant women are at higher risk of developing varicella pneumonia
• Shingles: reactivation of latent varicella-zoster virus