What is a Herpes Simplex Virus (HSV)

What is a herpes simplex virus (HSV) and how does it propagate?

HSV is a large, double stranded DNA virus. All the programming of the virus’ ability to infect someone is contained in the DNA. The DNA is packaged in a “diamond like” protein structure, called an icosahedron. The virus also has an “over coat”, the envelope, which is necessary for the “docking” procedure when the virus infects a cell. In other words, an HSV particle without the envelope is not infectious, since it cannot enter the cell.

How does HSV enter the body?

The virus gains entry into the body, not through intact skin, but through mucous membranes, such as the oral region, vagina, tip of the penis, or the eye. The virus will first replicate (make copies of itself) inside surface cells at these sites, eventually killing the infected surface cells. In a person with normal immunity, the immune system is quickly mobilized to contain the primary infection.

However, before this happens, the virus gains entry to the nerve cell end-plates (structures that help us to feel things like pain and temperature), present at the skin surface. The end-plates connect to the more deeply located nerve cell body through an elongated nerve fibre or axon. This cell in turn is connected to “serially coupled” layers of internal nerve cells, which eventually lead to a ganglion, which is a collection of nerve cell bodies just like a node in an electricity grid. Through such intricate connections the nerve cells eventually lead into and communicate with the central nervous system or the brain. The axons are protected by “myelin blankets”, just like the insulating material around electrical wires, but the endings are bare, as are the nodes where one nerve cell extension connects with the next (synapse). It is thought that the virus sheds its envelope as soon as it has entered the nerve and uses the axon as a conduit, hiding from immune system attack, as if it were inside a “Trojan Horse”.

HSV has specifically chosen the nerve cell body and ultimately the ganglion (HSV-1 resides in the trigeminal ganglion; HSV-2 resides in the sacral ganglia) as a site where it remains dormant. It is from these locations that the virus may reactivate from its dormant state to the respective innervated (nerve-cell-serviced) body areas. This is why dormant virus from the trigeminal ganglion (oral or facial area) reactivates in the oral or facial region, whereas the dormant virus from the sacral ganglion (lower back/spine area) reactivate to the genital area or the buttock.

What is latency (or where does the herpes virus lie dormant)?

Within a day of infection, the naked virus (nucleocapsid) arrives at the nerve cell nucleus, and it “injects” its genetic material (DNA).It then resides in the nerve cell nucleus in a dormant (latent) form.

According to most researchers, virus replication will not occur at this stage and no new virus particles will be formedThe precise molecular mechanisms for this event (establishment and maintenance of latency) are unknown, but appear to reflect an interplay between viral and nerve cell factors.

However, other researchers argue that a low level of replication must occur in order to keep the virus machine “well oiled”. This could be compared to car maintenance. For proper functioning, it is not a good idea to leave a car in the garage for years, but to drive it at least occasionally. If this were the case for HSV, it would likely result in low level viral shedding at the peripheral skin site.

Why does HSV recur (or why does the dormant herpes virus reactivate)?

It is important, from the virus “survival” point of view, to be able to “fire up” and begin to replicate should circumstances become uncomfortable inside the neuron (i.e. the infected person suffers a trauma, acquires a severe disease, becomes immunocompromised, or dies).

We do not understand why stress and sunshine, for example, tend to trigger HSV reactivation. When this happens, new virus particles are created and transported back to the skin and mucous membranes through the neuronal highway. They then begin to replicate in the surface cells, creating a blister in the form of a cold sore or genital herpes. The surface cells balloon up and become filled with fluid. This fluid contains millions of infectious viral particles.

We believe that the infected nerve cells usually survive during this reactivation process. We also think that HSV particles not only travel down to the skin and mucous membranes, but may also travel in the opposite direction leading them closer to the brain. Some researchers suggest that healthy immunocompetent people may, in fact, harbor dormant virus inside the brain.

How is HSV transmitted/How do I get it?

HSV spreads from person to person by direct contact with infected secretions, such as through kissing or sexual intercourse.

Click on any of the Herpes images below to enlarge.

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