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  • Alex Cloherty

Herpes hide and seek: Why do cold sores return?


When most people think of the Herpes Virus, they think of the sexually transmitted type. But, there is a whole other type of Herpes out there that you might actually be more familiar with: the kind that causes cold sores.

If you or somebody you're close to has a cold sore, you probably already know that once you get one, it will return again and again. Usually, they reappear after bouts of stress, exhaustion, excessive partying… They hit a lot of University students, that's for sure! But why is it that cold sores don't just go away eventually? Why do they keep returning?

The Herpes Virus which causes cold sores, known in academic circles as Herpes Simplex Virus 1 (HSV-1), is able to return again and again because it hides out in human nerve cells. To understand how this happens, you first need to understand that cells are like birds: they have feathers.

The outside surfaces of cells are more or less completely coated with feathery structures sugars and/or proteins. To sneak into nerve cells, also called neurons, HSV-1 first grabs onto a particular kind of protein-sugar feather found on the surface of cells. Once it has a hold on these feathers, the virus can then force the fusion of its own membrane and the membrane of the cell. You can picture this like two soap bubbles merging to become one.

This soap-bubble merger of the membranes of the virus and neuron allow the "seed" of the virus to enter the cell. This "seed" is called a capsid, and is where the genetic material (DNA) of the virus is contained. Once the capsid has entered the neuron, HSV-1 can travel along the nerve cell in a similar manner to rabies, as was explained in last week's post.

HSV-1 travels upstream along the neuron until it hits the area where the neuron's DNA is. Once there, the DNA of the virus can basically hang out with the cell DNA, blending in with its surroundings. By blending in this way, the virus is less visible to the human immune system. In fact, the virus accomplishes the whole process of grabbing, entering, and traveling along the neuron within only about 24 hours of infection, to get to this stage before the whole "immunitarmy" of the human body can assemble!

Once the virus is hidden with the neuron's DNA, it hides out for life. However, it doesn't cause symptoms, namely cold sores, unless a lot of virus can be produced.

It's thought that the virus is probably always producing more of itself, including its capsid (the "seed") and membrane (which can fuse with neuron's membranes). However, these mature viruses, complete with capsid and membrane, are probably produced only at very low levels. This is because your immune system is able to take them out as soon as they are no longer camouflaged with the neuronal DNA.

It's only when opportunity strikes that the virus rears its ugly head again. This opportunity, as you may have guessed, is usually when your immune system is low due to other reasons, such as during periods of illness, stress, high alcohol intake… You get the idea. The strength of the immune system also decreases with age, meaning that older adults might notice their cold sores reappearing more often than in early adulthood – which is when infection usually takes place for reasons that I'm sure I don't have to explain.

So if you're not yet infected, how do you avoid herpes hiding out in your nervous system? The main preventative steps are, don't share drinking containers and avoid kissing people with active cold sores.

Until next time - kiss responsibly!

- Alex

#viruses #infection #dormancy

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