Science Questions

If you get cold sores and give blood, can the virus be passed on?

Sun, 9th Dec 2007

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Question

Hazel asked:

If you get cold sores and give blood, can the virus be passed on?

Answer

Good question.  There’s probably almost zero chance of that. The virus that causes cold sores, the Herpes Simplex Virus (HSV), most of us acquire this when we’re very young because of our parents kissing us and children dribbling over each other in nurseries – it spreads in saliva.  When you first get it, it produces a sore throat, ulcers in the mouth, swollen glands in the neck and a high temperature.  It then invades the sensory nerves that supply your mouth and tongue, as well as other parts of the body it can infect.  It goes inside these nerve cells and switches off.  It exists there as a piece of DNA, loitering alongside the cell’s own DNA, and periodically comes back to life.  We don’t know exactly what triggers it to come back to life, but we know that things like damage to the skin, for example sunburn, menstruation, depression and immune depression, can bring it out again.  The virus turns back on its DNA, makes new virus particles which come down the nerve and pop out of the skin, causing the infectious lesion, the cold sore.  When you kiss someone who’s got one, that’s how you pick it up.  

Thankfully, it doesn’t really get into the blood stream, so you should be safe from HSV from blood products.  Other members of the herpes family do spread through blood, but not HSV.

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