Lauren Bentley
CRA
04.02.10

Disease

Herpes Simplex Virus Type Two

Causative Agents

The Herpes Simplex Virus Type Two (HSV-2) belongs to the Herpesviridae family.  It is enveloped, double-stranded DNA that is 150-200 nanometers (def) in diameter.  The virus is able to attach to and penetrate non-dividing host cells.  Once inside the cell, the virus replicates inside the nucleus.

Epidemiology

HSV-2 is one of the most common sexually transmitted diseases in the United States.  It is estimated that as many as one million people a year in the United States become infected with the virus.  At the 2010 National STD Prevention Conference, it was stated that one in six Americans ranging in age 14 to 49 years old is infected with HSV-2.  These rates have been found to be significantly higher in females (20.9%) than males (11.5%), most likely because women might be more biologically susceptible than men.  There also seems to be a higher prevalence of HSV-2 among African Americans (39.2%) versus Caucasians (12.3%).  The amount of people infected with HSV-2 tends to increase with age due to people living with the disease their entire lives because of its incurable nature.  Rates of infection are highest during adulthood and adolescence, since at these stages people tend to become more sexually active, and possibly have more than one sexual partner.  There currently appears to be no differences in the incidence of geographic location, since HSV-2 is common throughout the country in both rural and urban regions.

Transmission

Sexual contact is the most common manner in which HSV-2 is transmitted.  This means that there must be intimate contact with a person who is shedding the virus, and a host who is not infected.  Direct contact must be made with a lesion of an infected individual, or contact must be made with their body fluid through sexual intercourse, for example.  Once this contact occurs through the skin or mucous membranes, the herpes simplex virus begins to replicate in the epithelial cells (def), after four to six days of incubation.   As replication gets underway, cell lysis (def) and a local inflammatory response (def) occur, causing the lymphatic system to become involved.  At this point, the virus goes up along the peripheral sensory nerves until it reaches the dorsal root ganglia (def).  Replication continues here, and the virus is spread by the peripheral sensory nerves to other mucosal and skin surfaces.  Once the virus reaches the epithelial cells, replication continues even further until lesions form at the initial infection site.  The infection is eventually controlled through both systemic immunity (def) and mucosal immunity (def).  At this point, latency (def) of the virus is established once the virus travels along the sensory nerve pathways and reaches the dorsal root ganglia once again.

Transmission is also possible when the infected person is experiencing asymptomatic shedding (def).  This can happen over a week after or even before an outbreak, and occurs most frequently within the first year of being infected with the virus.  Asymptomatic shedding is the most common way in which HSV-2 can be transmitted, since the infected person is unaware that they are shedding the virus because they are experiencing no visible symptoms.

Without the use of any protection such as condoms or antiviral drugs, there is an 8-10% risk of women contracting HSV-2 from an infected male.  This is higher than the risk of an infected woman transmitting the virus to a man, with the risk only being 4-5%.  HSV-2 can also be transmitted from an infected mother to her baby.  The transmission risk is highest at 30-60% if the mother has an outbreak when delivering the baby.  This risk decreases greatly to 3%, however, if the infection is recurring, and drops further to 1% if there are no visible lesions present on the mother.

Signs and Symptoms:

HSV-2 is often difficult to diagnose since almost 80% of infected people have either mild or absent symptoms, allowing them to go undiagnosed.  In many cases, laboratory testing must be used to make a correct diagnosis.  These tests include skin biopsy, a culture of the virus, polymerase chain reaction (PCR) (def) which tests for the incidence of viral DNA, and direct florescent antibody (DFA) (def) studies to detect the virus.  When the virus is active, it appears as blisters or lesions on the infected area, which contain infectious particles of the virus.  These blisters can last anywhere from 2-21 days, and are then followed by a remission period, in which the sores disappear.  This latency is established when the HSV-2 reaches the dorsal root ganglia, and in this form, the DNA cannot be identified unless certain molecular probes are used.

Many people infected with HSV-2 often experience reoccurring outbreaks during their first year of infection.  Before the development of blisters, in subsequent outbreaks, prodrome (def) often occurs.  The symptoms that accompany this are itching, tingling and sometimes pain in the area where a sore will form. This can occur several days before, or even a few hours before a blister appears.  During reoccurring outbreaks, fewer blisters than the first outbreak often develop, and they tend to be less painful and heal faster.  Reoccurring outbreaks are also random, and occur approximately 4-5 times a year, with fewer occurrences after the first year of infection.  After several years, most infected people build up immunity to the virus, resulting in no further outbreaks. However, even though outbreaks are no longer experienced, the infected person is still contagious to others.

Prevention and Treatment

There has yet to be a cure developed for HSV-2.  Once one is infected, the virus stays with them for life since the immune system never removes it from the body.  Antiviral medicines, however, can lessen the severity of the symptoms of the outbreaks, their length, and how often they occur.  They also can reduce asymptomatic shedding.  These medications work by slowing down the replication rate of the virus, which gives the immune system a chance to intervene with the viral replication.  Examples include, valacyclovir (Valtrex), famciclovir (Famvir), penciclovir (Denavir) and acyclovir (Zovirax).   Topical treatments can also be used to relieve the symptoms of pain and itching and include tetracaine, lidocaine, and prilocaine. 

Due to the high prevalence of HSV-2, and its lack of a cure, preventative strategies are necessary for all sexually active people.  They include disclosure between partners, avoiding sexual contact during an HSV-2 outbreak, and consistent and proper condom usage.  Condoms offer moderate protection against HSV-2, reducing people’s risk of infection by 50%.  It is not possible for the virus to penetrate a latex condom, however, the effectiveness of a condom is limited because it provides no protection for the upper thighs, scrotum, anus and buttocks, all of which are areas susceptible to infection.  Preventing contact with these infected areas, and wearing a condom, should theoretically provide enhanced protection.   Condom -use has proven to be more effective in preventing an infected female from transmitting the disease to their male partner.  The use of daily antiviral medications and condoms during sex, further decreases the risk of transmission to the uninfected partner, when one partner is infected with HSV-2 and the other is not.  The two effects can be roughly added and provide a 75% reduction in transmission risk.

Bibliography

Baron, Samuel. Herpes Simplex Viruses, Clinical Manifestations and Pathogenesis. Medical Microbiology, 4th edition. 1996. Retrieved March 26, 2010 from http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=mmed&part=A3612#A3613
CDC. Tracking the Hidden Epidemics Trends in STDs in the United States 2000.  Herpes. April 6, 2001. Retrieved March 26, 2010 from  http://www.cdc.gov/std/Trends2000/herpes.htm.
CDC. Tracking the Hidden Epidemics Trends in STDs in the United States 2000.  A Closer Look at Herpes. Retrieved March 26, 2010 from  http://www.cdc.gov/std/Trends2000/herpes-close.htm.
Foster, Melissa. Prevalence of Genital Herpes Remains High. March 9, 2010. Infectious Disease News. Retrieved March 26, 2010 from http://www.infectiousdiseasenews.com/article/61733.aspx
MicrobeWiki. Herpesviridae. June 6, 2006. Retrieved March 26, 2010 from http://microbewiki.kenyon.edu/index.php/Herpesviridae
 Wikipedia. Herpes Simplex. Retrieved March 26, 2010 from http://en.wikipedia.org/wiki/Herpes_simplex