Chickenpox is a highly infectious condition caused by a virus called varicella zoster, which comes from the herpes group of viruses. It is common in the UK but less so in the United States since routine immunisation started there from the mid-90s.
Most cases in the UK occur before the age of five, although chickenpox may occur at any age. Once a person is exposed to the virus, it may take from nine days to three weeks before symptoms develop. A person is infectious from around four days before the rash develops until all the lesions have scabbed over.
Many people are concerned that children may develop shingles from someone else who has chickenpox. This is not possible - you can only contract shingles from yourself. Once someone has had chickenpox, the virus never leaves the body, but instead lies dormant in the spinal cord. In some instances, perhaps during times of stress or if the immune system is under par, the varicella zoster virus will travel along a nerve causing a localised skin rash, shingles.
A patch of shingles will shed virus and may cause chickenpox in someone who has never been exposed to it before. In most cases, children will catch it from another child who also has chickenpox. It is possible, but quite unusual to get chickenpox more than once.
Exposure in pregnancy
Many parents ask about the risks of exposure to chickenpox during pregnancy. If a mother has had chickenpox in the past, prior to pregnancy, she will be immune and the unborn child unharmed. If, however, she has never had it, and is exposed in the first half of the pregnancy, the child has a one in 200 to one in 50 chance of being affected by the virus.
Congenital varicella may cause poor growth, brain damage, a small head, cataracts, skin scarring, limb problems and even death. If contracted late in pregnancy, the child may be born with chickenpox, which may be fatal. Antibody and antiviral drugs are available to reduce these risks.
Symptoms
Some children will have no symptoms from chickenpox after exposure to the virus. In others, the first symptoms will be a high fever, feeling generally unwell, headache and perhaps stomach pains. Itchy spots, which become filled with fluid, known as vesicles, tend to occur all over the body but spare the arms and legs. They eventually crust over, after which they no longer shed virus.
Complications
Adults infected with chickenpox tend to have a far more severe course than children. But children may still experience significant complications from chickenpox. Young babies, those with other serious diseases and children with poor immune systems are particularly at risk.
Lesions affecting the eye may cause permanent damage. Vesicles may also occur in the mouth and genitalia, causing significant distress.
The vesicles may commonly become infected by bacteria, known as 'bacterial super-infection'. Super-infected lesions will look more inflamed than the others. Super-infection may require antibiotics and is more likely to cause scarring and changes in the pigment of the skin. The middle ear may also become infected by bacteria, causing otitis media.
Very rarely, bacterial infection can cause bone infection, or osteomyelitis; blood poisoning, or septicaemia; spreading skin infections, or cellulitis; or severe flesh infections, referred to as necrotising fasciitis. Some of these infections require hospitalisation and life-saving treatment.
Pneumonia is another unusual complication of chickenpox. In this situation, the virus affects the lungs, causing breathlessness, wheeze and chest pain.
The varicella zoster virus may rarely cause a brain infection called encephalitis. In this case, children become very irritable and drowsy, finding it difficult to balance and walk. They may also have symptoms of meningitis - headache, painful eyes when exposed to light, and neck stiffness. Children with brain involvement require hospital treatment, usually in an intensive care setting.
Treatment
The treatment of chickenpox usually requires rest and over-the-counter medications to control fever. Antihistamines and calamine lotion may be used to control itching. Anti-viral drugs and antibody therapy is available for severe cases.
Parents should be warned to keep their child away from susceptible individuals such as pregnant women and those whose immune systems are poor, such as people receiving chemotherapy for cancer.
Fortunately, the serious complications of varicella are rare, but if in doubt, always seek advice from your doctor.
- Dr Raj Thakkar BSc(Hons) MBBS MRCGP MRCP(UK) is a full-time GP in Buckinghamshire