Here are some facts about chickenpox, a miserable ailment rendered fairly rare since the advent of an effective vaccine:
— That's not its real name
We call it chickenpox. But this disease, which was once a part of most childhoods, is actually caused by the varicella-zoster virus.
These days, cases of chickenpox are less common as a result of the introduction of the varicella vaccine. The vaccine, administered on its own or combined with the vaccines for measles, mumps and rubella, is given in two doses in childhood.
It's one of the more effective vaccines. The U.S. Centers for Disease Control and Prevention says about 80 per cent of vaccinated people are fully protected. About 15 to 20 per cent could still contract chickenpox, but will have a milder course of disease and will recover more quickly.
— It's itchy and it scars
You'd be hard pressed to find an adult over the age of 20 or so who doesn't have a chickenpox scar somewhere on their body. (The first varicella vaccine was introduced in Canada in 1998.)
The disease causes a blister-like red rash that is very itchy. "Don't scratch!" was always the mantra in households with chickenpox cases, because scratching picks off the scab on the blister and that's what causes scarring.
— It's not just uncomfortable. It can also kill
Before the vaccine was introduced, most people caught chickenpox in childhood. It's one of the most contagious of the so-called childhood diseases, so if chickenpox hit a household or a neighbourhood, a lot of kids got sick.
In fact, some parents would throw "chickenpox parties" — assuming since their children would eventually get the disease, they might as well get it over with. (Public health officials discourage chickenpox parties; they would prefer parents vaccinate children.)
Most people who contract chickenpox feel awful for a few days but then get better. But chickenpox can lead to skin infections and pneumonia. It can also cause necrotizing fasciitis — flesh-eating disease — in rare case, as well as stroke and encephalitis (swelling of the brain).
Chickenpox complications are more common in children and adults with compromised immune systems. Chickenpox is risky for pregnant women, both for them and in some cases for the fetuses they carry.
The risk of death from chickenpox rises with age. In the pre-vaccination era in Canada, adults had the highest death rate — 30 deaths per 100,000 cases, according to the Public Health Agency of Canada. But the disease is also hard on infants, a group which had a death rate of seven per 100,000 infections.
— It's really infectious
The chickenpox virus spreads in the air through coughing or sneezing, says the CDC.
It can also spread if a vulnerable person touches or breathes in the virus particles that come from chickenpox blisters. A person who hasn't had chickenpox and hasn't been vaccinated can also catch the virus through contact with someone who has shingles. (More on shingles next.)
One of the things that makes chickenpox a terrific spreader is that people who are infected can transmit to others for a day or two before they even know they are sick. Once someone sick takes to their bed they have fewer chances of infecting others. But the virus can move around in that day or two before symptoms set in.
The varicella-zoster virus has a nasty trick. It remains dormant in the body of anyone who has had chickenpox, and can flare up later in life.
When the virus reactivates, it causes shingles — a painful skin rash. The CDC estimates about one in three people who have had chickenpox will have shinges.
It's not known what triggers the reactivation, though the risk seems to rise with age. More than half of cases occur in people 60 years of age and older.
There is an adult vaccine that significantly reduces the risk of developing shingles.
The Canadian Immunization Guide, http://www.phac-aspc.gc.ca/publicat/cig-gci/p04-vari-eng.php#a3.
The U.S. CDC: http://www.cdc.gov/chickenpox/about/bam-villain-for-kids-fs.html