Sunday, January 20, 2013

A mild dose

I mentioned a couple of posts back that I was having an interesting viral infection.   It's shingles - the illness you can get years after you've had chickenpox, when the varicella-zoster virus comes out of its hiding place on your nerves and gives you a skin rash with possible complications.

I don't like the way certain viruses do that "never leave your system" trick.  Like most in my family, I'm unlucky enough to get cold sores too, so now I've got two herpes related viruses always hanging around waiting to re-emerge if feeling run down.  (In fact, now that I think of it, how come people like me don't always get a break out of cold sores at the same time that they get shingles - both are thought to be related to the immune system dipping a bit.)

My chickenpox experience was as an adult and was of average unpleasantness, I guess.  My Mum had an attack of shingles in her 50's and it bothered her quite a bit for a couple of months; I remember David Letterman had one a decade or more ago which kept him off TV for a while.  So I was generally aware of the illness.  (One website says about 1 in 5 adults in Australia will have an attack.)

On Monday last week I noticed an itch on my back.  It felt a bit unusual, and looking in the mirror it seemed to be in a smallish oval red patch just off the spine, but I thought the redness may have just have been from scratching.  It was still looking like a rash on Tuesday evening though, and after checking some photos on the internet of what a shingles rash could look like, I headed off the GP.

He seemed to very much doubt it was shingles, as it was only moderately itchy, and didn't have any pain or much in the way of "pins and needles" feeling.   Anyway, he took a swab and gave me a week long course of anti-viral tablets just to be safe.

Over the next day or two, I asked everyone at work about whether they had shingles, and whether they had much pain with it.  As with the doctor, everyone I spoke to had the attitude "I think you'd really know about it if it was shingles - it's pretty painful."  Yet I was continuing with just mild itchiness.

The GP rang a couple of nights later and said the test was positive for the virus - it was shingles; just a very mild case apparently.  So I'll continue my anti-virals for a couple more days and just hope that is as bad as it gets.   (The rash is now less distinct and less itchy, but still there.)

I've had a look around at stuff on the internet about shingles.  I see that there is a vaccine they can give now for those aged over 60, when the complications can be worse.   But the most interesting thing I read was this - about how it is not clear whether widespread childhood immunisation against chickenpox may actually lead to more cases of adult shingles.  (I'll add a couple of the earlier paragraphs which set the scene before the most interesting bit):
 The varicella-zoster virus (VZV) is so named because it causes two distinct illnesses: varicella (chickenpox), following primary infection, and herpes zoster (shingles), following reactivation of latent virus....
  Herpes zoster or shingles is a sporadic disease, caused by reactivation of latent VZV in sensory nerve ganglia. It is usually self-limiting and is characterised by severe pain with dermatomal distribution, sometimes followed by post-herpetic neuralgia which can be chronic and debilitating in the elderly.10,11 Although herpes zoster can occur at any age, most cases occur after the age of 50 with the incidence of complications also increasing with age.12 However, children infected in utero or those who acquire varicella before the age of 1 year, and patients on immunosuppressive drugs or infected with human immunodeficiency virus, are also at increased risk of herpes zoster.13–15 A new herpes zoster vaccine which is over 60% effective in reducing the burden of herpes zoster and post-herpetic neuralgia16 has been available on the private market in Australia since 2008. The zoster vaccine is formulated from the same VZV strain (Oka-derived) as the licensed varicella (chickenpox) vaccines but is of higher potency (at least 14 times greater).
  In 1952, Hope-Simpson proposed the hypothesis that exposure to varicella may boost immunity against herpes zoster.20 There is increasing evidence to support that hypothesis, with two observational studies showing lower rates of herpes zoster in groups who have been exposed to varicella.21,22 If exposure to wild varicella provides boosting and protection against activation of herpes zoster, universal infant varicella vaccination and the subsequent decline in wild varicella may result in an increase in herpes zoster incidence among those previously infected.23 Mathematical modelling has also suggested that widespread infant varicella vaccination might result in a significant increase in the incidence of herpes zoster, possibly over a 40-year period.23 An Australian study, performed to assess the potential impact of universal varicella vaccination based on this hypothesis, suggested that total morbidity due to varicella and herpes zoster in Australia would decrease for the first 7 years of a population program, but, for 8–51 years after vaccination commenced, total morbidity was predicted to be higher than pre-vaccination levels.24 However, this model assumed 90% vaccination coverage and 93% vaccine effectiveness. These predictions might not be correct, particularly given that overall vaccine coverage and effectiveness are now estimated to be less than that originally used in the model. Currently, surveillance data from the USA, where varicella immunisation has been recommended for over a decade, indicates a large reduction in varicella morbidity with no increase in zoster disease yet demonstrated.25
Chickenpox and shingles are therefore a little complicated.  If they go the way of smallpox, good for us.

No comments: