Herpes Simplex Viruses

Herpes Simplex Viruses belong to the family Herpesviridae. The HSV viruses are double-stranded DNA viruses and replicate in the nucleus of host cells. They have icosahedral capsids and are enveloped viruses. HSV also consists of eight different types of viruses. The most commonly known viruses associated with HSV are HSV-1 and HSV-2. HSV infections are very common and by adulthood, almost 80% of Americans have had an HSV-1 infection at some point. About 20% of all Americans have had HSV-2 infections. Most infections caused by HSV are asymptomatic. Once a person becomes infected with HSV, the virus becomes latent between infections and remains in the body for life. HSV viruses are usually spread through contact with lesions on the skin. HSV-1 and HSV-2 have no seasonal incidence and are found worldwide. Over 90% of children older than 2 years of age in undeveloped countries have the antibody to HSV-1.

Taxonomy:  HSV-1 and HSV-2 viruses cause different types of infections in their hosts. HSV-1 causes gingivostomatitis, or oral herpes, which are cold sores along the oral mucosa and opening of the mouth. This type of infection occurs most often in children. About 80% of the American population has been infected by the time adulthood is reached. HSV-1 also causes keratitis which is an infection of the cornea, and can cause herpes encephalitis in older children and adults. HSV encephalitis is a rare disease and has a 70% mortailty rate. HSV is the primary cause of fatal sporadic encephalitis in the United States. HSV encephalitis is caused by HSV-2 in neonates and has a high association with immunocompromised patients. HSV-2 viruses can also cause genital herpes and neonatal herpes. About 85% of genital herpes infections are cause by HSV-2.

Pathogenesis: HSV viruses usually only infect humans although they can also be transmitted by dogs. Infections are spread through contact with secretions from lesions on the oral mucosa, genitalia, or areas where lesions have formed. Lesions develop on mucous membranes of the oral mucosa and genitalia after an incubation time period of 2 to 11 days. HSV is more readily transmitted when the virus is in its primary stage of development. The virus-infected cells are located at the base and along the edges of the lesions. The virus can still be transmitted from lesions that are old or scabbed. Also, asymptomatic patients can still transmit the virus without visible lesions present. Saliva and vaginal secretions contain the virus and the infection is spread through kissing, sharing drinking glasses, and through sexual contact. During latency of the virus, HSV-1 infects the trigeminal nerve root ganglion and autonomic ganglia of superior cervical and vagus nerves. HSV-2 remains in the sacral nerve root ganglion at the base of the spine. HSV infections can also be transmitted from mother to neonate and have a fairly high mortality rate of 60%, although infection obtained by this way is not as common.

Signs and Symptoms: Although many times HSV is asymptomatic, there are many signs to distiguish whether a person has an HSV-1 or HSV-2 infection. Oral herpes, is usually caused by an HSV-1 infection and has an incubation period of 2 to 14 days. In its primary stage, the virus is usually asymptomatic. When visible, the virus manifests into intraoral mucosa vesicles, which are inside the mouth and cannot be easily seen. The virus can also produce ulcerations which can be found on the buccal mucosa, posterior pharynx, gingival mucosa, and palatal mucosa. Since ulcerations may be found on the posterior pharynx, it may appear as pharyngitis. Recurrent infection usually causes lesions or infection of the lips and in the corners of the mouth where oral mucosa joins with skin. These lesions and ulcers create a burning sensasation which is typical of HSV infections.


Another sign of an HSV infection is the formation of genital herpes caused mostly by HSV-2. HSV-1 can also cause genital herpes and is the cause of infection about 33% of the time. In females, the infection appears as vesicles on the mucosa of the labia, vagina, or both. Infection can also occur in the urethra, on the cervix, or on the vuvla of the female body. In males, the infection affects the shaft, glans, and prepuce, and can also infect the urethra. These sypmtoms become less severe throughout recurrent infections.

HSV infection may also cause ocular herpes, or an infection of the eye. This will cause swelling of the eyelids and can also result in a corneal infection. HSV is the most common cause of corneal infections in the United States. Most infections only involve the epithelial layer of cells and with treatment, will heal completely.


What are the long term effects of HSV?

After primary infection of HSV, the virus remains inside the host. Although the person may be asymptomatic, the virus is still in the body and becomes latent. As discussed before, HSV-1 stays in trigeminal nerve root ganglia and autonomic ganglia of superior cervical and vagus nerves. HSV-2 remains in sacral nerve root ganglia. Certain stimuli can reactivate the virus such as stress, caffeine, and sunlight. This would cause the virus to come out of latency and lesions will reappear. There is no cure for HSV, but treatments and testing are available. With treatment and while the virus is latent, a person may appear and feel completely normal. Although no symptoms are visible, reactivation of the virus is possible at a later time.

Who is at risk?

HSV does not have a higher incidence in patients with a medical or family history of HSV. This also does not help to diagnose the disease. However if a neonate contracts HSV, it is very likely it was transmitted congenitally during birth from the mother. HSV in neonates can cause HSV encephalitis. Mothers who are expecting should be tested if an HSV infection is suspected. HSV is a common infection throughout the world and traveling will not increase your risk of contracting HSV. People who are sexually active before age 17, have been sexually active for many years, and who have had many sexual partners are at a greater risk. Also, people infected with other STDs such as gonorrhea, syphilis, and HIV are more likely to be seropositive for HSV.

How can an HSV infection be prevented?

HSV can be prevented by limiting sexual partners and practicing safe sex. HSV-1 and HSV-2 can still be transmitted when no symptoms are present so be aware of who your sexual partners are. Also be aware of lesions on or around the mouth and genitalia. Avoid direct contact with lesions, saliva, mucosal secretions, and other secretions from an infected person. Health care workers should wear gloves to prevent herpatic whitlow, which is an HSV infection on the fingers. There is no vaccine available to prevent against HSV.

How is HSV treated?

HSV can be treated by the use of antiviral drugs such as Acyclovir and Vidarabine. Daily doses of these drugs interefere with the replication of the virus so the virus is unable to reproduce in the host. Therapy, with the use of antiviral drugs, can limit recurrences of the disease althought it cannot completely prevent further infection.

For more information on HSV visit Herpes.com

This website is part of a class assignment for Clinical Immunology and Virology at the University of Delaware. I am a Medical Technology student and my goal is to educate people on HSV and help them to know more about how to prevent contracting an infection due to HSV. My Home Page          

Have any questions or comments?

CONTACT INFORMATION:
Laura Manzi
lmanzi@udel.edu

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