Chickenpox Varicella Infection

Related Subjects: |Herpes Varicella-Zoster (Shingles) Infection |Chickenpox Varicella Infection |Varicella Cerebral Vasculopathy |Herpes Viruses |Herpes Zoster Ophthalmicus (HZO) Shingles

About

• The varicella-zoster virus (VZV) causes two distinct clinical infectious diseases, chickenpox (varicella) and shingles (zoster).
• Chickenpox is the primary infection caused by the varicella-zoster virus. It is an acute, highly infectious disease most commonly seen in children under 10 years old.
• Chickenpox is usually a mild, self-limiting illness and most healthy children recover with no complications. Adults tend to suffer more severe disease than children.
• The incidence of Chickenpox is seasonal reaching a peak from January to April when outbreaks of infection are common. Anyone who has had chickenpox in the past may develop shingles.
• You can only get shingles if you have previously had chickenpox as it is a recurrence or reactivation of the varicella zoster virus.
• It is not possible to develop shingles from exposure to a person with chickenpox.
• It is possible however, to develop chickenpox as a result of exposure to a person with shingles. Second attacks of chickenpox are rare but do occur.

Transmission

• Chickenpox is highly contagious, infecting up to 90% of non-immune people who are exposed to the disease.
• The incubation period (the time from becoming infected until symptoms appear) ranges from 10 to 21 days although is usually from 14-16 days.
• Susceptible individuals who have been in contact with a person with chickenpox should be considered potentially infectious from the 10th to the 21st day after exposure.
• The most infectious period is 1-2 days before the rash appears, but infectivity continues until all the vesicles have crusted over, at least 5 days after onset of the rash.
• Airborne respiratory droplets. Direct contact with the vesicle fluid. Indirect contact through contact with clothes/linen freshly soiled by vesicle fluid
• Chickenpox can also be spread from people with shingles. A person with shingles can spread the VZV virus to others who have never had chickenpox.
• The exposed person would need to come in contact directly or indirectly with the vesicle fluid of the person with shingles but would develop chickenpox and not shingles.

Clinical

• Chickenpox may initially begin with cold-like symptoms, as the virus is shed from the nasopharynx for up to 5 days before the rash appears.
• This may be accompanied by fever, mild headache and myalgia. Vesicular rash starts as small papules
• An intensely itchy, vesicular (fluid-filled blister-like) rash appears - these crops of vesicular spots appear, mostly over the trunk and to a lesser extent the limbs. Later they crust.
• The rash usually appears first on the trunk and successive crops of vesicles appear over several days although hands and feet are relatively spared.
• The severity of infection varies and it is possible to be infected but show no symptoms. Infectivity may be prolonged in people with altered immunity.

Complications

• The risk of complications varies with age and is higher in infants under 1 and in persons over 15 years.
• Nearly all children recover completely and have detectable antibodies for many years.
• Complications in childhood are uncommon but may occur and include neurological complications (meningitis, encephalitis) and more rare glomerulonephritis and myocarditis.
• In children under 5, skin bacterial super infection is the most common complication.
• This manifests as a sudden high grade temperature (often after initial improvement), erythema and tenderness surrounding the original chickenpox lesions.
• Adults with chickenpox may develop more severe disease with lung involvement of varying severity, with smokers at higher risk of fulminating varicella pneumonia.

Varicella in Pregnancy

• Maternal VZV infection – associated with increased morbidity including pneumonia in 10-14% (severity is increased in later gestation) with 1% mortality; hepatitis and encephalitis
• Fetal Varicella syndrome – can occur from the 3rd to 28th week gestation with in-utero infection leading to dermatomal skin scarring, eye defects, limb hypoplasia and neurological abnormalities.
• Varicella infection of the newborn – due to maternal infection near the time of delivery or immediately post-partum, or from direct contact with a person other than the mother with chickenpox or shingles.
• Severe infection is likely to occur if the infant is born within 7 days of the onset of the mother’s rash, or the mother develops the rash up to 7 days after delivery.

Investigations

• Clinical diagnosis
• Laboratory confirmation is rarely required but if necessary, is available by sending a microscopy slide with vesicle fluid to the National Reference Laboratory.
• Serology is also available and is used to demonstrate immunity.

Management

• Isolate patient. No specific treatment for chickenpox. It is a viral infection that will therefore not respond to antibiotics. Treat to reduce fever and itchiness.
• Assess if at risk of serious complications and consider if needs Aciclovir and/or immunoglobulin to prevent severe illness from developing. See below.
• High Risk patients
  • Non Immune
  • Neonates
  • Immunosuppressed people e.g. receiving chemotherapy or radiotherapy
  • Organ transplant
  • Immunosuppressant therapy
• Varicella prevention in those at increased risk
  • If previously infected, very likely immune (95% positive predictive value). If any doubts check VZV IgG. Consider also if exposure.
  • If seronegative (non-immune), avoid contact with chickenpox/shingles and to inform healthcare workers of a potential exposure without delay.
  • If seronegative with significant exposure, VZIG (Varicella Zoster Immunoglobulin) should offered as soon as possible subject to its availability (discuss with on-call virologist first). VZIG is effective up to 10 days after contact or in case of continuous exposure, 10 days from the appearance of rash. Due to limited availability of VZIG, Public Health England (PHE) has recommended the use of VZIG for seronegative pregnant women with significant exposure in the first 20 weeks of pregnancy (up to and including 20+0 weeks) and either oral antivirals (oral acicolvir 800mg 4 times a day from days 7-14 after exposure or oral valaciclovir
• Management of Chicken Pox in Pregnancy
  • Pregnant women who develop a chickenpox rash should immediately contact their GP and avoid contact with potentially susceptible individuals
  • Pregnant Women with respiratory symptoms or other symptoms and signs of severe chickenpox (photophobia, seizures, drowsiness, haemorrhagic rash, bleeding or a dense rash with or without mucosal lesion) should be referred to the hospital immediately. A hospital assessment should also be considered in a woman at high risk of severe or complicated chickenpox even in the absence of concerning symptoms or signs.
  • High-risk women
    • Smokers
    • Chronic lung disease
    • Immunosuppressed (systemic corticosteroids in the preceding 3 months)
    • Second half of pregnancy.
  • Assess in an area away from other pregnant women. Treatment decided with a multidisciplinary team includes an obstetrician or fetal medicine specialist, a virologist and a neonatologist.
  • Women hospitalised with varicella should be nursed in isolation from babies, potentially susceptible pregnant women or non-immune staff.
  • Symptomatic treatment to prevent secondary bacterial infection of the lesions.
  • Prescribe Oral aciclovir (800 mg five times a day for 7 days) if pregnant with chickenpox and present within 24 hours of the onset of the rash and if they are 20+ weeks of gestation or beyond (dosage 800mg five times a day for 7 days). Use of aciclovir before 20+0 weeks should also be considered. However, Aciclovir is not licensed for use in pregnancy and the risks and benefits of its use should be discussed with the woman.
  • Intravenous aciclovir should be given to all pregnant women with severe chickenpox - take advice.
  • VZIG has no therapeutic benefit once chickenpox has developed and should therefore not be used in pregnant women who have developed a chickenpox rash.
  • If the pregnant woman develops varicella or shows serological conversion in the first 28 weeks of pregnancy, she has a small risk of FVS (incidence of 0.91%; lower in the first trimester) and she should be informed of the implications.
  • Women who develop chickenpox in pregnancy before 28 weeks should be referred to a fetal medicine specialist, at 16–20 weeks or 5 weeks after infection, for discussion and detailed ultrasound examination.
  • Women who develop varicella infection during pregnancy should be counselled about the risks versus benefits of amniocentesis to detect varicella DNA by polymerase chain reaction (PCR). Amniocentesis should not be performed before the skin lesions have completely healed.

References

• Chicken Pox (Varicella Zoster virus)guideline (GL805)