The complex problem of herpes simplex

There are thankfully few conditions for which anyone might suggest wearing a bag over your head. Oral herpes is one. In an advert for aciclovir cream (the antiviral medication that can slightly reduce the duration of an outbreak) a woman wears a sack with two holes cut out of it for her eyes. Older adverts featured a man wearing an upturned bucket. Magazines and the internet are full of hopeful remedies for cold sores: tea tree oil, ice cubes, garlic … But at least oral herpes gets some press. No one even speaks about the genital variant, which is still described in some studies as the most embarrassing sexually transmitted infection of all – more stigmatised, even, than HIV.

The herpes viruses are some of the commonest viruses to afflict humans – by some estimates 80 per cent of the adult population will carry type one herpes simplex by the age of 80 – but they are also some of the most misunderstood. Herpes is a broad category – it includes the virus that causes chickenpox and shingles (varicella zoster) as well as the germs responsible for glandular fever and Kaposi’s sarcoma. Cold sores and genital herpes are caused by the two herpes simplex viruses. Type one usually infects the skin of the face: it causes the blisters that we call cold sores. Type two usually causes genital herpes. However, this is a description of prevalence, rather than a rule: in practice, you can get either type at either end of the body, and there is no clinical way of differentiating between the two.

Herpes simplex spreads by contact. The virus “sheds” infective particles, especially when there are sores present (though you can still shed when there’s absolutely nothing to see). If the particles get through your own skin’s defences, you will contract the infection (though, again, you won’t necessarily develop any symptoms). Cold sores are so common that most people are exposed in infancy, though they may not get a sore until adolescence. Genital herpes is also more widespread than you might expect: the World Health Organisation estimates a prevalence in western Europe of up to 18 per cent of women and 13 per cent of men.

The word herpes is derived from the Greek herpein “to creep”, and the capacity of herpes simplex to lie dormant, or latent, is part of what makes it difficult to understand. It helps if you can visualise its target: the nerve cell. The Mr Men books are useful for this. A nerve cell looks like Mr Tickle’s arm. The long wiggly part – the axon – terminates in a waving hand. The hand has a cell body for a palm, from which emerges lots of splayed fingers, or dendrites. The dendrites like to hold hands with the dendrites of other nerve cells, forming clusters of intertwined fingers called ganglions. This is where latent herpes simplex goes to hide.

After an initial infection, the virus retreats down the axons of the nerve – the trigeminal nerve in the case of cold sores, or the sacral nerve if it is a genital infection. It then lurks mutely in the ganglia of that nerve. It won’t do anything dynamic – that is, recur – unless your body’s immune surveillance is temporarily compromised, by stress, for example, or sunlight, or another illness.

At this point it may creep back up the axon to the area of skin supplied by that nerve, where it typically causes fluid-filled blisters followed by scabs. This can happen at any time: it may be months distant from the initial infection. As a character in the film The Hangover observes, “What happens in Vegas, stays in Vegas. Except for herpes – that shit’ll come back with ya.”

Sophie Harrison is a hospital doctor in South Yorkshire.

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