Childhood immunisations are a series of vaccines that are given to infants and young children. Immunisation…
What is chickenpox?
Chickenpox, also known as varicella, is a common, very contagious childhood illness. It is caused by the varicella virus and is most common during the cooler months of winter and spring. In temperate climates, chickenpox is primarily a childhood disease. In tropical climates, however, chickenpox is often more common among adults.
Prior to the global introduction of routine childhood immunisation, over 90% of people were infected with the virus, usually as children.  The illness is normally mild and goes away on its own, but in a minority of people it can cause more severe complications. Adults who get chickenpox tend to suffer more severe symptoms and are at greater risk of complications. The virus can also stay inside the body, re-emerging decades later to cause the adult illness known as shingles.
Chickenpox is caused by the varicella zoster virus (VZV). The virus is very common; an estimated 90% of all unvaccinated people have been infected with it at some point.
The virus is highly contagious, meaning that an unvaccinated person, who hasn't previously had chickenpox, has a high chance of being infected if they are in the presence of an infected person with whom they share household or office items, etc.
When an infected person sneezes or coughs, the virus spreads into the air via millions of tiny droplets, each containing many viruses. If a droplet enters your nose or mouth, you may then become infected. The droplets can also collect on surfaces and objects, so you can also catch the virus by touching an infected surface and then touching your nose or mouth area.
The varicella virus can also be caught by coming into contact with the fluid in the rash blisters.
Chickenpox is most common in children under 10 years of age, but anyone can catch chickenpox if they have not been infected or vaccinated in the past. However, some people are at greater risk of developing severe symptoms and complications (see below). These may include:
Signs and symptoms
The varicella virus has an incubation period of 10-21 days between the infection and the appearance of first symptoms. However, people can infect others from the time they themselves are infected.
The first symptoms of chickenpox can include:
- Lack of appetite, and;
- Mild stomach ache.
These symptoms go away naturally after a few days.
The most distinctive symptom of chickenpox is the rash it causes. It appears a day or two after the appearance of the early symptoms. The rash is very itchy. Blisters filled with clear fluid appear on the skin, with patches of reddish skin around them.
During the next 5-10 days, the blisters dry out and fall off on their own. It is important to not scratch the blisters, as it can lead to scarring, further infection and further spread of the virus.
Methods for diagnosis
Your doctor will diagnose chickenpox by noting the symptoms, especially the distinctive rash. For normal chickenpox cases, no further diagnosis is necessary.
If the illness becomes more serious, blood tests (checking for the presence of the virus and for antibodies formed against it) can confirm the diagnosis. Your doctor may wish to send samples for laboratory testing to confirm the presence of the varicella virus.
Types of treatment
Chickenpox usually goes away on its own without specific treatment. However, the symptoms can be very uncomfortable, especially the itching.
Medication that can help with the fever that often accompanies chickenpox may be recommended (aspirin is not recommended for children under 18).
Calamine lotion and wet compresses applied to the rash may help soothe the irritation. Antihistamine medication can help relieve itching.
Preventing further infection
Good hygiene - keeping the area clean, fingernails trimmed and not scratching - can help prevent further infection of the exposed blisters and avoid complications and scarring.
For some people, especially adults and people at risk of developing complications, antiviral medication, such as acyclovir, may be prescribed.
Treatment by vaccination
The varicella vaccine, if given within a short time after infection (preferably under three days, up to a maximum of five days), can reduce the severity of symptoms and shorten the course of the disease. However, the chickenpox incubation period is usually longer than five days, so by the time symptoms appear, it is already too late for this measure.
People at high risk of developing complications who cannot receive the regular varicella vaccine, such as pregnant women, newborn babies, or children with certain immune deficiencies, may be treated with antibodies that protect against the virus (varicella immunoglobulin).
Chickenpox is a common and usually mild disease and complications of chickenpox are rare. However, they can occur, especially in people in the abovementioned risk groups.
Bacterial and viral infection
Bacteria can infect the body as a result of chickenpox, especially through scratched skin. The varicella virus itself can also circulate throughout the body, causing problems.
Bacterial and viral complications can include:
- Cellulitis - infection of the layers of and under the skin;
- Lung inflammation (pneumonitis) and/or infection (pneumonia);
- Inflammation of the brain (encephalitis) and of the layers around the brain (meningitis);
- Blood infections (septicaemia);
- Disorders of the blood vessels, leading to a stroke in extreme cases, and;
- In rare cases, inflammation of the liver (hepatitis), kidneys (nephritis), or joints (arthritis).
Shingles is a skin rash caused by reactivation of the varicella virus. In people who have been infected with the virus, it can remain dormant in the nerve roots for long periods of time, sometimes decades, before erupting again.
Shingles usually appears as a rash on a specific area, most often running in a single band across the side of the body or the face. It is normally not dangerous, but can be highly uncomfortable and painful and may lead to unpleasant complications.
Congenital varicella syndrome
Most pregnant women are already immune to the varicella virus. A pregnant woman who is not immune and is infected with it during the first 20 weeks of pregnancy is in danger of passing the virus on to her foetus. The baby may then be born with congenital varicella syndrome.
- Skin scars;
- Growth retardation, abnormally small arms and legs;
- Eye defects, vision problems, and;
- Brain damage.
Other pregnancy complications:
- If the mother is infected with the virus during pregnancy, there is a small chance of miscarriage or premature birth;
- If the mother is infected with the virus in the second half of pregnancy, the baby may develop shingles in the first years of its life, and;
- If the mother is infected with the virus in the last week before birth, or in the week just after birth, the baby may develop chickenpox, which can be particularly severe and has an up to 30% mortality rate. 
A varicella vaccine is available and forms a part of regular childhood immunisation programs in many countries. It is often given as a part of the measles, mumps, rubella and varicella (MMRV) vaccine.
Japan and Korea introduced the vaccine in the late 1980s. It was gradually introduced into most other countries from the 1990s and has been listed on the Australian national immunisation program as part of routine childhood immunisation since 2005. Adults who have not been vaccinated as children may be encouraged to get vaccinated if they have not had chickenpox as children and are:
- At high risk of catching the virus (such as child education and healthcare workers), or;
- At risk of developing shingles.
Most vaccinated people, if later infected with the virus, will not fall ill. Of those vaccinated people who are later infected with the virus, 15%-20% will still get chickenpox - most of them with milder symptoms.  The vaccine will not cause shingles.
A person who has had chickenpox once is usually protected for life. It is very rare for people to be reinfected with the varicella virus and develop chickenpox a second time.
Preventing further infection
To prevent the spread of infection, children with chickenpox are advised to stay at home until the blisters have dried out and crusted over.