The Different Types of the Herpes Virus
The herpes virus is probably the most well-known virus after influenza (the flu) or the common cold. What most people don’t know is that this nasty little virus can take several different forms, eight to be exact. The most common form of the herpes virus is chicken pox, which is called varicella-zoster. Herpes simplex is the sexually transmitted version of the virus.
However, there is much more to the herpes virus than just chicken pox or genital herpes. For instance, after an active infection, the virus is shed (eliminated) in the urine and feces for up to several months (sometimes years in the case of the cytomegalovirus) after the active infection has resolved. This means the infected person is still contagious, which is what makes this virus so contagious. It can easily be transferred when the patient is asymptomatic.
The following is a brief synopsis of each of the different herpes viruses.
The Herpes Simplex Virus
The herpes simplex virus is probably the most well-known virus of the herpes family, and it is just as contagious. Herpes simplex infects epithelial cells and remains latent in neurons. HSV-1 causes recurrent oropharyngeal lesions, commonly known as “fever blisters" or "cold sores.” It is also the primary cause of sporadic encephalitis (inflammation of the brain), gingivostomatitis (inflammation of the gums and mucous lining of the mouth), and keratoconjunctivitis (severe dryness of the eye that involves the cornea) and dendritic corneal ulcers (also called HSV keratitis) in which the cornea becomes affected by herpetic lesions that look like the dendrites of neurons in the brain.
Its rapid growth cycle of approximately eight to sixteen hours begins at the site of infection. Because the virus fuses to the cells of its host, it easily spreads from cell to cell. The lesions on the surface of the skin are caused by the damage, and ultimate death, the virus causes to host cells.
First infections usually manifest in children; otherwise the infection is asymptomatic in most cases. Symptomatic cases in adults typically manifest as tonsillitis or pharyngitis.
Lymphadenopathy (swollen lymph nodes) may occur, but will remain localized to the area affected. Recurrent infections typically manifest in the trigeminal ganglia.
This results in excruciating pain in the jaw, the muscles involved in chewing and the facial muscles, including those surrounding the eye. Generally, only one side of the face is affected.
HSV-2 is responsible for genital herpes by infecting the genital mucosa (mucous lining of the internal anatomy of the genitalia).
Interestingly, although rare, HSV-1 can also cause genital herpes. The active virus can be asymptomatic or it may erupt with lesions, which is more common. Initial infection of genital herpes can last up to three weeks, and the lesions are very painful.
Fever, malaise, painful urination and lymphadenopathy located in the groin may occur simultaneously. After the infection resolves, the virus can be shed continuously for up to three weeks.
People who have had HSV-1 are less likely to contract HSV-2 than those who have not. Previous exposure to HSV-1 also decreases the severity of an HSV-2 outbreak. Reoccurrence of the virus is common, and the virus can be active yet asymptomatic. These infections are more likely to be contracted since the person isn’t aware the virus is active. Studies have shown that 50 percent of the cases of sexual transmission of the virus occurred during asymptomatic infections.
The Varicella - Zoster Virus
Also known as chickenpox, varicella-zoster is the milder form of the herpes virus and is typically found in children. However, it can occur in adults as shingles and is usually more severe especially if the adult is immunocompromised.
Both shingles and chickenpox are caused by the same virus, however varicella is the disease that follows an initial contact with the virus, and zoster is the reactivated form of it.
Varicella-zoster is transmitted though the mucosa of the respiratory system, specifically the upper respiratory tract, or the conjunctiva of the eye. Initial replication takes place in the regional lymph nodes, and then the virus spreads and replication begins in the liver and spleen. The virus is then transported to the skin where the rash develops. The incubation period of varicella is about 10 to 21 days.
Initial symptoms are fever and fatigue followed by the rash. The rash starts on the abdomen and then the face, limbs and mouth, respectively. The rash usually lasts about five days, and kids can develop several hundred lesions.
Cytomegalovirus or CMV
The cytomegalovirus contains more genetic material (DNA) than any of the other herpes viruses. It is also a ubiquitous virus meaning it’s everywhere, and there are many different strains of it.
Its incubation period is about 4 to 8 weeks because its replication process is much slower than that of either varicella-zoster or herpes simplex.
It is a systemic infection and has been found in the lungs, liver, esophagus, colon, kidneys, monocytes and lymphocytes. It also has a latency period, just like all herpes viruses, and it can be shed for months to years after the primary infection.
This virus can be transmitted to the fetus in utero if the mother has an active infection regardless of whether or not it is a primary infection or a reactivation. In fact, one percent of live births in the US have congenital infections.
Epstein - Barr Virus
Epstein - Barr Virus
Most people don’t know what Epstein-Barr is, let alone that is caused by the herpes virus. But it is the cause of mononucleosis.
It is suspected to be the cause of nasopharyngeal carcinoma, Hodgkin and non-Hodgkin lymphoma, Burkitt lymphoma and other lymphoproliferative disorders.
The cell this virus targets is the B lymphocyte. These cells mature in the bone marrow and are a type of mononuclear leukocyte cells - white blood cells with a one-lobed nucleus. The incubation period for the Epstein – Barr Virus (EBV) is about 30 to 50 days, and patients typically have enlarged lymph nodes and spleens. Some patients have signs of hepatitis.
EBV does not cause a rash of any kind; symptoms usually include a low-grade fever, malaise, sore throat, fatigue and headache. The fever and malaise can linger for months after the initial infection has resolved.
Replication Cycle of the Epstein - Barr Virus
Herpes Virus 6, 7, and 8
These viruses were found recently. Herpes virus 6 was only discovered in 1987; herpes virus 7 was isolated in 1990 and herpes virus 8 was found in 1994. Because of their recent discovery, very little is known about these three viruses.
Herpes Virus 6
Infection with this virus usually occurs in children and is most commonly referred to as “sixth disease,” or Roseola Infantum. It seems the virus has an affinity for T lymphocyte cells and is found in the saliva.
The virus initially infects the oropharynx for this reason. It is also assumed the virus is transmitted orally. Like all herpes viruses, HV – 6 can be reactivated, and this typically occurs during pregnancy or in patients undergoing some type of transplant.
Herpes Virus 6
Herpes Virus 7
First isolated from peripheral blood lymphocytes in a healthy patient, HV – 7 typically occurs in later childhood. The virus takes up residence in the salivary glands and is also found in the saliva. Although HV – 7 is a distinct virus from HV – 6, they share about 50 percent of the same DNA.
Herpes Virus 8
This virus is also known as Kaposi Sarcoma, or KSHV, and is closely related to EBV more so than any of the other herpes viruses. The most obvious feature of this virus is the way it affects the gene regulatory network.
The virus takes over genes that regulate the rate of mRNA transcription, allowing the growth of vascular tumors (Kaposi Sarcomas). The virus can be transmitted sexually, through blood or organ transplants or vertically (from mother to child).
Brooks, G., Butel, J., Carroll, K., Mietzner, T., Morse, S. (2010) Jawetz, Melnick & Adelberg's Medical Microbiology. New York, NY. McGraw Hill Lange
Virology I: How Viruses Work Columbia University, Vincent Racaniello, Ph.D (Professor)
Virology II: How Viruses Cause Disease Columbia University, Vincent Racaniello, Ph.D (Professor)
TWiv: This Week in Virology Podcast with Vincent Racaniello, Ph.D
© 2012 Melissa Flagg COA OSC