Chickenpox is caused by the:

Chickenpox (varicella) is a highly contagious disease caused by the varicella-zoster virus (VZV), a member of the herpes virus family. It mainly affects children under the age of 10, but people of any age can get it.

Chickenpox spreads through the air when an infected person coughs or sneezes, and by direct contact with the fluid from the blisters. A person is infectious from about one or two days before the rash appears until all the blisters have formed scabs. The incubation period is about 10-21 days.

Symptoms include fever, tiredness and loss of appetite, followed by an itchy rash. The rash starts as red spots, which turn into small fluid-filled blisters (vesicles), which then burst and form crusts or scabs. The rash usually appears first on the chest, back and face, and then spreads over the body. Blisters appear in successive crops, so spots at different stages can be seen at the same time. In most children, the disease is mild and lasts about 5-10 days. It can be more serious in adults, newborns, pregnant women and people with weak immunity, causing complications such as pneumonia.

After a person recovers, the virus is not removed from the body. It stays dormant (inactive) in the nerve cells. Years later, especially in older people or those with weak immunity, it can become active again and cause shingles (herpes zoster), a painful, blistering rash usually on one side of the body along a nerve.

One attack of chickenpox usually gives lifelong immunity against getting chickenpox again. A live attenuated chickenpox vaccine, developed in Japan by Michiaki Takahashi in 1974, is available. Treatment includes rest, fluids, calamine lotion for itching and, in some cases, antiviral drugs such as acyclovir. Aspirin should not be given to children with chickenpox, as it can cause Reye's syndrome.

Why not the other options?

• ✗The variola virus caused smallpox, which has been eradicated.
• ✗The rubella virus causes German measles.
• ✗Mycobacterium leprae is a bacterium that causes leprosy.