Herpes and Herpes Virus
Herpes and herpes virus
Herpes is a name given to a common viral infection. The infection can occur in the mouth and in the genitals.
The two forms of herpes are caused by two forms of a herpes virus. Both forms are called herpes simplex virus. Oral herpes is generally caused by herpes simplex type 1 (that is typically shortened to HSV–1). It is also known as human herpes virus 1 (HHV1). Genital herpes is generally caused by herpes simplex type 2 (shortened to HSV–2, which has also been called human herpes virus 2, or HHV2). However, HSV–1 can cause genital herpes and HSV–2 can cause oral herpes.
There are eight herpes virus types known in humans. HSV–1 (HHV1) and HSV-2 (HHV2) are the forms associated with oral and genital herpes. Human herpes virus 3 is also known as varicella zoster virus , and is the cause of chickenpox. HHV4 is the official name of Epstein-Barr virus , the major cause of infectious mononucleosis . HHV5 is also known as cytomegalovirus. It can cause mononucleosis, hepatitis in newborns, and complications in AIDS patients. HHV6 causes roseola in children and fever-associated seizures in infants. HHV7 has not yet been associated with any disease, and appears to be present in almost all people. Infection with HHV7 likely occurs early in life. Finally, HHV8 contributes to Kaposi's sarcoma, a relatively rare cancer that predominantly afflicts AIDS patients whose immune systems are failing.
Herpes simplex virus types 1 and 2 appear identical when examined using the high magnification power of the electron microscope . Both types are icosahedral in shape; that is, their surface consists of twenty equal-sized and equilateral triangles.
The oral form of herpes is manifest as cold sores or socalled fever blisters, and is common in young children. The virus can be passed from person to person very easily. Only a brief contact is needed for transmission. Cold sores are innocuous in children and adults. However, they can be a very serious health threat in newborns.
The genital form can be apparent as genital sores. These appear as clustered blistery-appearing sores on the vagina, vulva, cervix, penis, buttocks, or the anus. Pain, itching, and a burning feeling during urination can accompany the sores. In more severe cases, the lymph glands can be swollen, with a number of flu-like symptoms evident. These symptoms of what is referred to as primary herpes persist for several weeks then disappear. They can return, usually to a lesser extent, in anywhere from a few weeks to years later. Others who are infected may not display any symptoms whatsoever. Diagnosis of infection in asymptomatic people can still be made, based on the detection of viral antibodies in the blood.
Herpes affects some 80 million people in the United States alone, with one in six of these people having genital herpes. Herpes is spread by human contact. Typically this involves kissing, touching, or sexual contact. Typically, a person is contagious when he or she has open sores. Because of this, contact with others can be minimized when sores are present, thus minimizing the chance of spread. However, it has been proven that genital herpes can be spread even when no symptoms or sores are evident. The chance of this happening is about 10 percent. The spread of herpes via wet toilet seats and the like is now considered to be unlikely.
Studies have shown that the chances of pregnant women passing either herpes simplex virus to the developing fetus are rare. Transfer can occur during childbirth. If open sores are evident at this time, a caesarean section may be considered to avoid the chance of infection.
Herpes simplex virus replicates insides cells of the host. An association between a virus particle and the surface of the host cell starts this process. The host cell is typically that in nerves. This association is specific, involving the recognition of a host surface molecule. Another viral protein then associates with several of the host cell molecules that are collectively termed the herpes virus entry mediators. This second association leads to the fusion of the host and the viral membranes. The contents of the virus can then be emptied into the host cell.
Once in the host cell, the viral deoxyribonucleic acid genetic material somehow enters the nucleus . The viral DNA is then replicated using the transcription machinery of the host. The viral transcription process occurs immediately with certain stretches of the viral DNA and a bit later with other stretches of the DNA. The early gene products participate in the replication of the later regions of the viral DNA.
New virus particles can be produced very soon after infection. Or, alternatively, the infection may become what is described as latent. In a latent infection, no viral particles are produced. Viral DNA continues to be replicated along with host DNA until such time as a signal stimulates the transcription of viral genes that are involved in the assembly of new virus particles. Stress, surgery, menstruation, and skin infections such as sunburn are known to be signals, although the molecular nature of these stimuli is unclear.
Recurrence of symptoms can be more frequent with people whose immune systems are compromised, such as those with leukemia or acquired immunodeficiency syndrome (AIDS). Currently there is no cure for herpes. Physicians can prescribe one of three medications to treat genital herpes. These are acyclovir, famciclovir, and valacyclovir. With or without medication, in general the recurrences become fewer with the passage of time, often ending after five to six years.
Despite this fading of symptoms, the herpes simplex viruses can be debilitating aside from their direct affects. They can deplete the body's immune resources, leaving someone more vulnerable to infection by another microbial agent.
See also Latent viruses and diseases; Virus replication