Herpes

Herpes refers to the diseases caused by Herpes Simplex Virus (HSV), an important cause of human disease. In people symptomatic herpes siplex infections take two common forms, a recurrent rash of swollen blisters in the area of the mouth, and a similar rash in the area of the genitals. The two subtypes are responsible for cold sores and genital herpes, a recurrent, painful genital rash. Genital herpes is considered a sexually transmitted disease (STD).

The virus

Herpes Simplex Virus (HSV) is a member of the Herpesviridae family of viruses, a family of DNA viruses important in human disease. These include Human herpesviruses (HHV)1-8 (see Herpes Viruses). HSV 1 and 2 correspond to HHV 1 and 2. HSV 1 and 2 are very prevalent in the human population, with as many as 30-70% of people testing positive for antibodies in their lifetime.

Natural history of human infection

HSV 1 and 2 are DNA viruses that cause common human illnesses. In both types, once infection is established it is life-long.

In general, HSV 1 is more commonly seen on the face, and also accounts for a large minority of genital infections. HSV 2 is more commonly seen on the genitalia.

The virus is spread by simple person-to-person contact and can occur when sores are visible, and when the virus is dormant, although this is less effective. These viruses generally cause mucocutaneous infection. This can manifest as cold sores on the lips, or as genital sores. The typical rash is described as "dew drops on a rose pedal". These are generally painful. Initial infection can be accompanied by systemic systems such as fever and muscle aches. After resolution of the initial infection, the virus becomes dormant in the human host. Under certain conditions that are not well understood, the virus is reactivated, with a recurrence of mucocutaneous infection. These recurrent attacks are unpredictable and can be frequent or infrequent. In addition to the common mucocutaneous infection, HSV 1 and 2 can also cause keratitis (inflammation in the eye), encephalitis (brain infection), and severe neonatal disease if acquired during pregnancy.

Diagnosis

The diagnosis of a herpes simplex infection is ordinarily a clinical one, that is- it is made by a trained health care provider based on the history and physical findings, rather than on labratory tests. However, a clinical diagnosis does not distinguish between HSV-1 and HSV-2 infection, except by probability. Confirming a diagnosis and clarifying the actual virus type involve requires laboratory testing. The most definitive proof of infection, the "gold standard" of diagnostic test, is the growth of the virus in artificial culture from a specimen taken from the patient's lesions. Although primary ulcers have a high rate of viral shed, recurrent lesions shed virus at a much lower rate, and so culture of recurrent lesions has a high false negative rate. Accordingly, in patients with typical presentations of recurrent outbreaks known to be caused by the Herpes Simplex virus, failure to culture the virus in no way overturns the diagnosis.

Viral culture is an expensive laboratory test that must be carried out for 10 days in order to assume negative results.

"PCR techniques are more sensitive than viral cuture and results can be available in less than 4 hours". (reference for quote:Sullivan M. Sams R 2nd. Jamieson B. Holt J. Clinical inquiries. What is the best test to detect herpes in skin lesions?. Journal of Family Practice. 55(4):346, 348, 2006 Apr.)

Diagnostic tests on the immune response to the virus can determine not only the subtype of herpes simplex infection but whether the outbreak is primary or recurrent. HSV-1 and HSV-2 each have respective variations in virally produced glycoprotein G, and immunoglobulin G (IgG) produced by an infected person differs accordingly. If an individual is making IgG to either type of virus, 1 or 2, infection is confirmed. If the individual has cear signs of a genital herpes infection, but the tests for IGG are negative, the most likely explanation is that this is a primary outbreak, and the patient has not yet begun production of that type of antibody. Confirmation of that presumed diagnosis of a primary herpes infection can be made on follow-up testing, with demonstration of anti-HSV IgG levels.

Oral herpes infection

Cold sores are most commonly caused by HSV-1 and are ubiquitous in distribution in human populations. Here, the vesicles have crusted over and begun to heal.

Genital herpes infection

In population studies in the United States, both serotypes of the herpes virus are prevalent in symptomatic genital herpes infections. HSV-2 accounting for more than half, and HSV-1 for almost half, of iall nfections. More than 50 million people are infected in that country, making this the most common STD in the USA.

Although both types of herpes simplex virus can account for genital herpes, and cause a very similar appearing rash, "HSV-1 has a much lower recurrence rate. For example, 40% of patients with an initial episode of HSV-1 will remain asymptomatic during the first year of infection, while 40% of patients with an initial outbreak of HSV-2 will have six or more recurrences per year." (reference for quote:Kirkland LG. New developments in the management of STDs. [Review] [10 refs] [Journal Article. Review] Nurse Practitioner. 31(12):12-21; quiz 22-3, 2006 Dec. UI: 17149130 )

The Center for Disease Control (CDC) in the United States recommends that genital lesions be cultured in order to determine the type of HSV infection.

Ophthalmologic herpes simplex infection (eye)

"Herpetic eye disease is among the most common causes for infectious uveitis. It may affect healthy as well as immune-compromised hosts, although its clinical presentation varies accordingly."

Herpes simplex infection in neonates

Although herpes infection is aggravating in healthy adults, it is a lethal disease in very young babies.

"Neonatal HSV disease is acquired at 1 of 3 distinct times: intrauterine (in utero); peripartum (perinatal); and postpartum (postnatal)" (reference for quote: Kimberlin DW. Diagnosis of herpes simplex virus in the era of polymerase chain reaction. Pediatric Infectious Disease Journal. 25(9):841-2, 2006 Sep.) Among pregnant women in the United States, "greater than 60% are positive for HSV-1...Overall, 60–80% of neonatal herpes is associated with the primary or first-episode genital herpes acquired in close proximity to delivery."ref for quote:Tita AT. Grobman WA. Rouse DJ. Antenatal herpes serologic screening: an appraisal of the evidence. [Review] [49 refs] [Journal Article. Review] Obstetrics & Gynecology. 108(5):1247-53, 2006 Nov. UI: 17077252)

"maternal acquisition of new infection in late pregnancy, ... accounts for 60–80% of neonatal herpes"(ref for quote:Tita AT. Grobman WA. Rouse DJ. Antenatal herpes serologic screening: an appraisal of the evidence. [Review] [49 refs] [Journal Article. Review] Obstetrics & Gynecology. 108(5):1247-53, 2006 Nov. UI: 17077252)

However, newborns have a limited immune system for the first 3 weeks of life, and even a kiss by a well-meaning friend or relative who bears a virus-shedding cold sore on the can cause infection, albeit rarely, in this vulnerable period.

Prevention and Treatment

Because HSV 2 is spread more commonly by sexual contact, it is easier to prevent than HSV 1. There is currently no vaccine available for either virus. Avoiding contact with people who have obvious sores helps reduce infection, and prophylaxis with commonly available antiviral drugs can help prevent transmission during the latent phase of the illness. Prophylaxis can also be given to reduce frequency and severity of attacks. Consistent and correct use of condoms reduces transmission.

References

Goldman: Cecil Textbook of Medicine, 22nd ed., Copyright © 2004 W. B. Saunders Company

Cohen & Powderly: Infectious Diseases, 2nd ed., Copyright © 2004 Mosby, An Imprint of Elsevier