Herpes Simplex (thing)

The word herpes was coined from the Greek word herpein meaning to creep. Herpes Simplex Virus (HSV)is about 180 - 200 nm in diameter and icosahedral in shape. The virus has an envelope, making it more resistant to chemical and physical damage. Herpes Simplex Virus is typically classified under two distinct strains, Type I and Type II, each responsible for a group of symptoms but sharing several common features. The major difference between type I and type II is the site of infection, Type I causing orofacial lesions and Type II causing genital lesions.

Features:

• Latency: This means that the virus has the ability to reside in the genome of certain human or animal cells and cause no symptoms. Stress can however stimulate the virus to start replicating rapidly and manifest as active lesions. It is important that a virus can infect cells that are not actively multiplying, such as neurons, for succesful latency, and HSV possesses this capability.
• The viral envelope : This is crucial for the penetration of the virus into the host cell. It contains certain enzymes that make this process easier.
• DNA Virus : The virus carries DNA as opposed to RNA so the DNA fragment must be entirely replicated. This implies that they must encode enzymes involved in nucleic acid metabolism and DNA synthesis to be able to copy their DNA once they have penetrated the host cell.
• Herpes viruses infect all known vertebrate species as well as at least some invertebrates (e.g., oysters); the viruses fall into at least three distinct lineages, all of which are believed to have coevolved with their host species (mammalian/avian, fish/amphibian and invertebrate). They are believed to be extremely ancient (hundreds of millions of years old, or older).

Infection

In the case of Type I, infection happens in about 80% of the population at a young age and usually causes no symptoms. This is referred to as a sub-clinical infection. The virus is spread by droplet infection. Type II infection is normally sexually transmitted.

HSV I affects the face, causing lesions around the eye and mouth, the latter being more common. Following infection, the virus migrates to the trigeminal nerve and lies there in a dormant state referred to as latency. In the case of HSV II, the virus resides in the sacral area following infection. Stress such as wind, sunburn and fever cause the virus to migrate down to the skin surface such as the lips and multiply rapidly causing the lesions associated with the virus. Cold sores are one such type of clinical manifestation.

Treatment

Apart from symptomatic treatment of lesions, antiviral treatment plays an important role in the control of such HSV infection. While eradication of the virus is difficult, drugs like Acyclovir, famciclovir, valacyclovir and penvir are used to treat HSV infection.