Varicella-Zoster Virus (VZV) Infection

Introduction

Varicella-Zoster Virus (VZV) is a highly contagious virus responsible for two distinct clinical conditions: varicella (chickenpox) as the primary infection, and herpes zoster (shingles) upon reactivation. VZV primarily affects children as chickenpox, while shingles typically occurs in older adults or immunocompromised individuals. VZV can lead to significant complications, particularly in those with weakened immune systems.

Aetiology and Pathophysiology

Varicella-zoster virus is a member of the herpesvirus family and shares characteristics with other herpesviruses, such as the ability to establish latency and reactivate later in life:

• Transmission: VZV is transmitted through respiratory droplets, direct contact with vesicular fluid from skin lesions, or indirectly through fomites. The virus is highly contagious, especially in the early stages of varicella.
• Latency and Reactivation: After the primary infection (chickenpox), VZV becomes latent in the dorsal root ganglia. Reactivation of the virus later in life causes herpes zoster (shingles), typically in the distribution of a single dermatome.
• Risk Factors: Risk factors for reactivation include advanced age, immunosuppression (e.g., HIV infection, cancer, organ transplantation), and stress.

Clinical Presentation

The clinical presentation of VZV infection differs based on whether the patient has chickenpox or shingles:

Varicella (Chickenpox)

• Prodromal Symptoms: Fever, malaise, and headache typically precede the rash by 1-2 days.
• Rash: The characteristic vesicular rash begins on the face, scalp, and trunk, spreading to the extremities. Lesions progress from macules to papules to vesicles, which then crust over. New lesions continue to appear in crops over 3-5 days, resulting in lesions at different stages of development.
• Pruritus: The rash is intensely itchy, and scratching can lead to secondary bacterial infection.
• Systemic Symptoms: Children often experience mild systemic symptoms, while adults may experience more severe manifestations, including high fever and general malaise.

Herpes Zoster (Shingles)

• Prodromal Pain: Localised pain, tingling, or burning in the area of the affected dermatome often precedes the rash by several days.
• Rash: The rash consists of grouped vesicles on an erythematous base, confined to a single dermatome. The most common sites are the thoracic and lumbar regions, but the trigeminal nerve, particularly the ophthalmic branch, can also be involved.
• Postherpetic Neuralgia: Persistent pain in the affected dermatome after the rash has healed is a common complication, particularly in older adults.
• Systemic Symptoms: Some patients may experience fever, headache, or general malaise, but these are less common than in varicella.

Diagnosis

The diagnosis of VZV infection is primarily clinical, based on the characteristic appearance of the rash. However, laboratory tests can confirm the diagnosis in uncertain cases:

• Clinical Examination: The classic vesicular rash of varicella or the dermatomal distribution of vesicles in herpes zoster is usually sufficient for diagnosis.
• Polymerase Chain Reaction (PCR): PCR testing of vesicular fluid, blood, or cerebrospinal fluid (CSF) is the most sensitive method for detecting VZV DNA and is particularly useful in atypical cases or immunocompromised patients.
• Serology: VZV-specific IgM and IgG antibodies can help distinguish between primary infection, reactivation, and immunity, though these tests are more commonly used in epidemiological studies.

Management and Treatment

The management of VZV infection depends on the clinical presentation and the patient’s age, immune status, and the severity of the disease:

1. Varicella (Chickenpox)

• Supportive Care: Management is mainly supportive, including antipyretics like paracetamol for fever, and calamine lotion or antihistamines for itching. Aspirin should be avoided in children due to the risk of Reye's syndrome.
• Antivirals: Oral aciclovir is recommended for adults, adolescents, and immunocompromised patients, especially if started within 24 hours of rash onset. It may also be considered for high-risk children.
• Prevention: The varicella vaccine is part of routine childhood immunisation in many countries and can prevent or reduce the severity of the infection.

2. Herpes Zoster (Shingles)

• Antivirals: Oral antivirals, such as aciclovir, valaciclovir, or famciclovir, are most effective when started within 72 hours of rash onset. These medications reduce the severity and duration of the rash and the risk of postherpetic neuralgia.
• Pain Management: Pain control is crucial and may include paracetamol, NSAIDs, or stronger analgesics such as opioids. In cases of severe pain or postherpetic neuralgia, gabapentin or amitriptyline may be prescribed.
• Topical Treatments: Topical lidocaine patches or capsaicin cream can be used to manage neuropathic pain.
• Prevention: The shingles vaccine is recommended for older adults to reduce the risk of reactivation and the severity of the disease.

Complications

VZV infections can lead to several complications, particularly in immunocompromised patients or those with severe disease:

• Bacterial Superinfection: Secondary bacterial infection of skin lesions, often caused by Staphylococcus aureus or Streptococcus pyogenes, can occur in both varicella and herpes zoster.
• Pneumonia: Varicella pneumonia is a serious complication that can occur in adults, pregnant women, and immunocompromised individuals.
• Neurological Complications: VZV can cause encephalitis, meningitis, or myelitis, particularly in immunocompromised patients.
• Disseminated Infection: In immunocompromised patients, VZV can disseminate to multiple organs, leading to a severe and potentially fatal illness.
• Postherpetic Neuralgia: Persistent neuropathic pain following herpes zoster is the most common complication in older adults.
• Herpes Zoster Ophthalmicus: Reactivation of VZV in the ophthalmic branch of the trigeminal nerve can lead to serious eye complications, including keratitis, uveitis, and vision loss.

When to Refer

Referral to a specialist may be necessary in the following situations:

• Severe or Complicated Disease: Patients with severe VZV infection, such as disseminated disease, pneumonia, or neurological involvement, should be referred for specialist care.
• Immunocompromised Patients: Immunocompromised patients with VZV infection require specialist management due to the increased risk of severe disease and complications.
• Postherpetic Neuralgia: Patients with persistent pain following shingles may benefit from referral to a pain specialist for management of postherpetic neuralgia.
• Ophthalmic Involvement: Immediate referral to an ophthalmologist is necessary if herpes zoster affects the eye or the periorbital area.

References

1. British Association of Dermatologists (2024) Guidelines for the Management of Varicella-Zoster Virus Infections. Available at: https://www.bad.org.uk (Accessed: 26 August 2024).
2. National Institute for Health and Care Excellence (2024) Varicella-Zoster Virus Infection: Diagnosis and Management. Available at: https://www.nice.org.uk/guidance/ng99 (Accessed: 26 August 2024).
3. British National Formulary (2024) Antiviral Treatments for Herpesviruses. Available at: https://bnf.nice.org.uk/ (Accessed: 26 August 2024).