Common Skin Infections

Herpes zoster and varicella zoster

Varicella is the term used to describe classical ‘chickenpox’. The incubation period is ­21 days and there may be an influenza – like prodrome prior to the rash. The rash classically starts centrally and then spreads, particularly to areas not exposed to pressure e.g. axillae; it is rare on the palms or soles. Lesions appear in crops, initially appearing as macules and then developing into papules, which become vesicular and then crust as the vesicles burst. There are usually lesions at all stages visible. Recovery from infection gives lifelong immunity. The virus remains latent in one or more posterior root ganglia. Remember infection may be more severe in adults, in immunocompromised and in smokers who are at risk of developing Chicken pox pneumonitis.

Clinical Tip: Look in Axillae (often involved) and look for lesion 'Dew Drop on a Rose Petal'- vesicle on erythematous base

Varicella – note lesions at different stages in development

Dew Drop on Rose Petal

Herpes zoster refers to the reactivation of varicella zoster virus causing a unilateral rash in a single dermatome (shingles), most commonly the ophthalmic branch of the trigeminal nerve and on the trunk in the distribution of T5-L2. The rash may be preceded by an area of paraesthesia and hyperaesthesia where the rash develops and with weakness in the affected or adjoining limb. The rash is also vesicular and heals with crusting. The majority of cases occur over the age of 50 years.

Clinical Tip: Asking about preceeding dysaesthesia in the skin is a really helpful way to aid making the diagnosis, particularly if you are not sure.

Herpes zoster – note the dermatomal distribution

What if the rash is not confined to one dermatome? How can you determine whether the infection is primary or a reactivation (shingles)?

This is initially determined from the history. Questions to ask:

• Is there a history of chickenpox
• Has there been any contact with chickenpox?  Patients are infectious from 24-48 hours prior to the rash and until all vesicles have crusted, usually 5-7 days. Spread occurs via respiratory droplets. In practice spread will only occur after a prolonged period of time in close proximity e.g. 15 mins face­ to face contact or 30 mins in the same room. Contact prior to 48 hours before the rash can be disregarded.
• What age is the patient? Zoster is more common in the elderly, but may occur in children with a history of varicella occurring in utero or in infancy. Healthy children presenting with shingles therefore may sometimes need to be investigated for causes of immunosuppression.
• Is the patient immunosuppressed? Very immunosuppressed patients e.g. those receiving chemotherapy, may occasionally present with ‘disseminated shingles’ i.e. several dermatomes affected. They will also be generally unwell with a fever and tachycardia and should be referred to hospital for intravenous Aciclovir. 

Clinical Tip: Multi-dermatomal shingles can be a presenting sign of HIV infection and should ring alarm bells.

 

Laboratory diagnosis

1.  Serology: is this primary or secondary? If it is unclear whether the patient has had varicella in the past a serum sample (clotted blood) should be sent to the lab for varicella IgG. If this is positive this indicates past infection and therefore immunity. Patients with zoster will have pre­existing IgG antibody. Patients with chickenpox may be positive for VZV IgM antibodies but are often seronegative at presentation. If a blood sample is sent at the onset of the rash a repeat specimen should be sent after recovery to detect seroconversion (development of IgG).

2.  Direct immunofluorescence: is this varicella? The simplest and fastest way of obtaining a diagnosis of varicella is by sending a scraping from the base of a vesicle on a slide to virology, and a swab from the base of the lesion in viral transport medium for culture. 

Infection control and contacts

Anyone without a past history of varicella is at risk of developing the disease after exposure. The disease can be more serious in adults, particularly those who smoke, due to the risk of varicella pneumonitis. Immunosuppressed individuals and neonates are at increased risk of haemorrhagic or disseminated varicella. There is also an increased risk of varicella pneumonitis in pregnant women, along with the risk of congenital varicella syndrome in the foetus. Congenital varicella syndrome includes limb hypoplasia and skin scarring, microcephaly, cataracts and growth retardation. The risks to the foetus have been estimated to be less than 1% in the first 12 weeks pregnancy and approximately 2% between weeks 13 and 20. After this gestation maternal infection may cause herpes zoster in the infant, up to the week before and after delivery when infection can be severe or fatal in the infant.

First determine whether contact occurred in the infectious period (see above). Pregnant women whose immune status is unknown should have an urgent VZIgG assay requested (obtain advice from the lab). This can be done the same day by the lab if necessary. Human varicella zoster immunoglobulin (VZIG) is recommended as prophylaxis for individuals fulfilling all of the following three criteria.

(a) a clinical condition which increases the risk of severe varicella e.g. immunosuppression, pregnancy, neonates

(b) no antibodies to varicella

(c) significant exposure to chickenpox or herpes zoster

VZIG is obtained from the virology department and is only effective if given within 10 days of exposure, preferably within 72 hours. It does not prevent infection but may attenuate disease.

Healthcare workers without varicella antibodies should not have contact with patients during their incubation period, returning to work 21 days after exposure. Individuals who have received VZIG have longer incubation periods. Ideally the immune status of immunocompromised patients should have been checked and susceptible individuals should be immunised and advised to avoid contact with infected individuals.

Apart from the issue of timing of the contact, as described earlier, the type of contact and closeness and duration of contact are important. The need for VZIG is restricted to those in contact with chicken pox, disseminated zoster, immunocompetent individuals with exposed lesions (e.g. ophthalmic zoster) or immunosuppressed individuals with lesions anywhere (viral shedding may be greater). A significant duration of contact would be 30 mins or more within the same room, or face-­to-face contact e.g. having a conversation. Transmission from household contacts is particularly efficient.

To obtain VZIG contact your local virology department for advice. It will either be issued from the department itself or from Public Health Laboratories and the Communicable Disease Surveillance Centre (CDSC).

In the UK varicella vaccine is available privately but the UK's immunisation body decided against universal vaccination of children. Patients not immune to chickenpox who are at risk of complications from varicella if they are exposed, may discuss vaccination. It may also be recommended for healthcare workers and close contacts of immunosuppressed who are not already immune. The vaccine is given as two separate injections, usually into the upper arm, four to eight weeks apart. The varicella vaccine is effective in making about 90% immune. The vaccination cannot be given in pregnancy and pregnancy should be avoided for 3 months after the injection.

Management of chicken pox

Children: it is a self-limiting illness and management is supportive. They should avoid pregnant women and immunosuppressed patients (but, not necessarily other children). Aspirin should not be given due to the risk of Reye’s syndrome, a syndrome of encephalopathy and liver damage associated with varicella and influenza. Topical antipruritics such as Calamine lotion are very old fashioned but do seem to afford relief from itch. A mild antihistamine may be advised.

Adults: treatment is also supportive, but they should be monitored for complications of varicella. Treatment with aciclovir is indicated for otherwise healthy adults presenting within 24 hours of the rash who smoke and/or have chronic lung disease and pregnant women in the second half of pregnancy. Treatment is also indicated in adults who develop respiratory symptoms and a fever (may require intravenous therapy therefore seek specialist advice- there is also a risk of permanent lung fibrosis).

• Secondary bacterial infection of skin

• Viral pneumonia occurs in 1 in 200 adults (compare with 1 in 200,000 children) 10% smokers increased risk in immunocompromised individuals and pregnancy.
• Haemorrhagic chicken pox. Lesions may appear purpuric. May be associated with thrombocytopenia and disseminated intravascular coagulation so seek specialist advice.
• Encephalitis cerebellar ataxia in children- most recover fully but it may take months. More common in immunocompromised. 3-4/100,000 cases in children.

Management of Shingles

Early treatment with high dose acicilovir (800mg orally 5 times per day) has been shown to reduce zoster-associated pain, produce faster resolution of the rash and decrease eye complications. Oral famciclovir (dose 250mg three times tds) seems to be as effective. There is some evidence that low dose amitryptiline given early also helps reduce intensity and duration of pain. Prednisolone given acutely with aciclovir reduces acute symptoms but does not seem to shorten duration of zoster associated pain (ZAP). Sympathetic nerve blocks have been reported anecdotally to reduce ZAP. Mild opiate analgesics will provide relief during the acute attack. Furthermore, gabapentin, a GABA analogue has been shown to reduce pain of three months duration. Carbamazepine should not be used- this is effective in trigeminal neuralgia, not herpetic neuralgia. Acupuncture may provide pain relief for some patients, along with topical measures such as ice packs and capsaicin. Patients with intractable pain may benefit from referral to a specialist pain clinic.