Chickenpox is an acute, infectious disease caused by the varicella-zoster virus (VZV). Chickenpox is highly contagious, infecting up to 90% of non-immune people who come into close contact with an infected person.
The initial symptoms of infection are mild fever and headaches. These are followed within hours by the appearance of a typical rash. Crops of red spots appear over 3 to 5 days, which quickly develop central fluid-filled blisters that are intensely itchy. After a few days these crust over and dry up. The rash mostly affects the trunk, but may appear anywhere on the body, including the scalp and the mouth. In about one in ten cases symptoms are so minimal the infection goes unnoticed.
The virus is transmitted by direct contact with the rash, by droplets dispersed into the air by coughing or sneezing or through contact with infected articles such as clothing and bedding. The incubation period (time from becoming infected to when symptoms first appear) is from 14 to 21 days.
The most infectious period is from 1 to 2 days before the rash appears but infectivity continues until all the blisters have crusted over (commonly about 5 to 6 days after onset of illness).
Anyone who has never had the disease or who has not been vaccinated against varicella-zoster virus can get chickenpox. The majority of people are infected in childhood and remain immune for life.
Chickenpox is most commonly seen in children under 10 years old and spreads quickly within child care facilities, schools and families.
Chickenpox is usually a mild illness and most healthy children recover with no complications; however the illness is usually more severe in adolescents and adults.
Certain groups of people, such as neonates (infants within the first four weeks of life), adults, pregnant women and those who are immunocompromised due to illness or treatments such as chemotherapy or high-dose steroids may experience more serious complications.
These include viral pneumonia, secondary bacterial infections and encephalitis (inflammation of the brain). Very rarely, chickenpox infection can be fatal even in previously healthy people.
Varicella infection in pregnant women can cause severe chickenpox with increased risks for the mother from varicella pneumonia and other complications. It also carries the risk of congenital varicella syndrome for the unborn baby. Congenital varicella syndrome can cause a range of problems including shortened limbs, skin scarring, cataracts and growth retardation.
The risk of this occurring within the first half of pregnancy has been estimated to be less than 1% in the first 12 weeks and around 2% between 13 and 20 weeks of pregnancy. Between 20 and 28 weeks, the risk is substantially lower.
Infection with in the later stages of pregnancy can cause premature delivery or neonatal chickenpox infection. This is particularly serious if the mother becomes infected 7 days before birth.
Treatment of chickenpox is generally based on reducing symptoms such as fever and itchiness. People at higher risk of developing serious complications from chickenpox or shingles may be given antiviral drugs such as acyclovir and/or immunoglobulin (a specialised preparation of antibodies taken from the plasma of blood donors), which may prevent severe illness developing. Immunoglobulin is offered to non-immune pregnant women who have been in contact with someone with chickenpox or shingles.
Chickenpox occurs worldwide and is endemic in most countries. In temperate climates, it usually occurs in sporadic outbreaks, particularly during the winter and spring.
It is estimated that in the UK, 9 out of 10 people have had chickenpox by the age of 15 years. However, adults from tropical or subtropical areas are less likely to have had chickenpox in childhood.
Chickenpox is not a notifiable disease in Wales or England (although it is in Scotland). However, information about the trends in incidence of chickenpox in Wales is available through the Public Health Wales Sentinel GP Surveillance Scheme. A volunteer sample of 40 general practices in Wales (covering over 10% of the population of Wales) have reported cases of measles, mumps, rubella, shingles, chicken pox, pneumonia (from 2004) and influenza each week to CDSC Wales since 1986.
The latest GP surveillance newsletter is published weekly on the Public Health Wales Health Protection Division internet site can be accessed from the link: GP Surveillance Newsletter
Two live, attenuated varicella vaccines are licensed in the UK. At present, there are no plans for varicella vaccine to be given routinely to all children in the UK but it is recommended for children aged 1 to 12 years who are close family contacts of those people considered to be at high risk of severe chickenpox or shingles infection. It is also licensed for healthy adults and children over 13 years old who are not immune to varicella (as indicated by blood tests).
Since 2003, varicella vaccination is now recommended following advice from the Joint Committee on Vaccination and Immunisation (JCVI) for non-immune healthcare workers who work in primary care and in hospitals (both NHS and private). This recommendation covers all non-immune staff who have direct patient contact including ambulance drivers, ward cleaners, catering staff and GP receptionists.
Public Health Wales issue guidance and advice to both health professionals and the general public in Wales on the management and treatment of such infections, especially in outbreak situations and in those considered to be more at risk of developing complications from the illness.