Herpes Simplex 1 Virus
Herpes Simplex 1 Virus
Disease History, Characteristics, and Transmission
Introduction
The Herpes Simplex 1 virus (HSV-1) causes painful sores, known as cold sores, on the skin or in the eyes. Less frequently, HSV-1 can cause genital ulcers. HSV-1 is closely related to HSV-2, which is the virus generally associated with similar lesions in the genital area (known sometimes just as “herpes”). Both HSVs belong to the Herpes family of viruses, all of which exist as viral particles of diameter around 200 nm (nanometers), consisting of a protein exterior enclosing a molecule of doublestranded DNA. Other significant Herpes viruses include the Varicella-Zoster virus, which causes chicken pox, Epstein-Barr virus, and Cytomegalovirus (CMV). The Herpes virus invades cells, such as neurons, and may lie dormant for many years, causing no obvious symptoms. However, a herpes infection can be activated at any time and may often recur during life. Symptoms tend to occur only when the Herpes virus is active. Although the virus itself cannot be eliminated, symptoms of active infection, like cold sores, can be treated with antiviral drugs.
Disease History, Characteristics, and Transmission
HSV-1 often causes no symptoms when it first enters the body, creating a latent infection within nerve cells. However, in around one-quarter to one-third of those infected, it will eventually become active. Triggers for activation of HSV-1 include stress, sunlight exposure, fever, broken skin, and menstruation. When HSV-1 activation occurs, new virus particles are formed and may move from neurons to the mucous membranes of the body, such as the mouth, skin, and eyes.
HSV-1 reactivation is not always accompanied by symptoms. However, the virus particles may continue to replicate within surface cells, which then begin to swell, releasing fluid. This forms a blister—usually referred to as a fever blister or cold sore. Each blister contains millions of new virus particles and is highly infectious. A single blister or a cluster of them may occur, and they often recur around the same location on the upper or lower lip, nose, chin, cheeks, or inside of the mouth. The formation of a cold sore is often preceded by burning, tingling, itching, or pain in the area where the blister is going to form. The time between the warning signs and the appearance of the cold sore is typically a few hours to a day or so. Once the blister has formed, it breaks and produces a yellow crust. This falls off within a few days, leaving behind pinkish skin that heals without forming a scar. The whole process normally takes 8-10 days.
The fingers, generally around the fingernails (where the virus may enter through torn cuticles), are a common site of HSV-1 infection, which results in a painful condition known as herpetic whitlow. This area is especially vulnerable because it contains many nerve endings through which HSV-1 can be transmitted. Also, HSV-1 is the cause of Herpes gladiatorum—sometimes called “wrestler's herpes”—a herpes infection on the face, neck, chest, or arms that is spread via skin contact.
HSV-1 may also cause fever and swollen glands in children and tonsillitis, pharyngitis (throat infection), and even encephalitis (infection of the brain) among adults. Although HSV-1 encephalitis is rare, it still accounts for about 10 percent of cases of this infection in the United States.
HSV-1 is transmitted by person-to-person contact, via the mucous membranes—that is, through kissing and sexual intercourse. Contact with infected secretions from items such as cups, glasses, towels, and food is also a significant mode of transmission. In a person with an intact immune system, symptoms of reactivation may not be apparent, but they still make new copies of the HSV-1 virus. This phenomenon is known as viral shedding and leads to people without symptoms spreading HSV-1 unknowingly through the usual modes of transmission. HSV-1 can also be transmitted from mother to baby during childbirth, resulting in general infection of the newborn and possibly encephalitis.
WORDS TO KNOW
DORMANT: Inactive, but still alive. A resting non-active state.
IMMUNOCOMPROMISED: A reduction of the ability of the immune system to recognize and respond to the presence of foreign material.
LATENT INFECTION: An infection already established in the body but not yet causing symptoms, or having ceased to cause symptoms after an active period, is a latent infection.
VIRAL SHEDDING: Viral shedding refers to the movement of the herpes virus from the nerves to the surface of the skin. During shedding, the virus can be passed on through skin-to-skin contact.
IN CONTEXT: DISEASE IN DEVELOPING NATIONS
The eye is less commonly affected by HSV-1 infection, but when it happens, it can be very serious. Typically, HSV-1 infection of the eye occurs as conjunctivitis, affecting the membrane covering the cornea and inside of the eyelids. There may also be blisters and swelling of the eyelids. HSV-1 infection can lead to scarring of the cornea, and it is the most common cause of infectious blindness in the developed world.
Scope and Distribution
Herpes infections are found all around the world, but prevalence is influenced by age and socioeconomic status. In less developed countries, about one-third of children are infected by five years of age and this goes up to 70–80 percent by early adolescence. In developed countries, around 20 percent of children are infected by the age of five and 40–60 percent by early adulthood. People with weakened immunity, such as transplant recipients and HIV/AIDS patients, are more susceptible to serious HSV-1 infections. Those with eczema—whose skin is frequently broken or damaged—are often affected with widespread HSV-1 infection, a condition known as eczema herpeticum, which requires prompt treatment with antiviral drugs. Healthcare workers, such as anesthesiologists and dentists, are at risk of herpetic whitlow if their fingers come into contact with patients who have cold sores or through viral shedding from patients who are infected but do not have symptoms.
Treatment and Prevention
There is no cure for HSV-1 infection. Once the virus is present in cells, it is there for life, even though it may not cause any symptoms. However, there are a number of antiviral drugs that can treat the symptoms of cold sores. The main ones are acyclovir, valacyclovir, and famciclovir; the former can be used as a cream, a tablet, or an intravenous injection, but the other two are only available in tablet form. These drugs are most effective in treating a first episode of cold sores. An outbreak of cold sores can be prevented by using lip balm—to avoid broken skin—and minimizing stress and sun exposure. People who have cold sores should not kiss others and should keep any items such as cups, washcloths, and towels separate.
The TORCH test, which is sometimes called the TORCH panel, belongs to a category of blood tests called infectious-disease antibody titer tests. This type of blood test measures the presence of antibodies (protein molecules produced by the human immune system in response to a specific disease agent) and their level of concentration in the blood. The name of the test comes from the initial letters of the five disease categories. The TORCH test measures the levels of an infant's antibodies against five groups of chronic infections: Toxoplasmosis, Other infections, Rubella, CMV, and HSV. The category of other infections usually includes syphilis, hepatitis B, Coxsackie virus, Epstein-Barr virus, Varicella-Zoster virus, and Human Parvovirus.
IN CONTEXT: REAL-WORLD RISKS
The Herpes 1 virus is also the cause of a condition known as Herpes gladiatorum (a skin infection common in wrestlers, rugby players, and other athletes playing sports with extensive skin contact between competitors). First described in the 1960s, the Centers for Disease Control and Prevention (CDC) states that, “In a national survey of 1477 trainers of athletes approximately 3% of high school wrestlers were reported to have developed HSV skin infections during the 1984-85 season. Lesions occur most often on the head and neck. Primary infection may cause constitutional symptoms with fever, malaise, weight loss, and regional lymphadenopathy (a swelling of the lymph nodes). Ocular (eye) involvement includes keratitis (a swelling or inflamation of the transparent covering at the front of the eye that protects the iris and pupil), conjunctivitis (a swelling or inflammation of the conjunctiva often termed ‘pinkeye’), and blepharitis (a swelling or inflammation of the eyelids). Transmission occurs primarily through skin-to-skin contact.”
The CDC further states that, “Control methods should include education of athletes and trainers regarding herpes gladiatorum, routine skin examinations before wrestling contact, and exclusion of wrestlers with suspicious skin lesions.”
SOURCE: Morbidity and Mortality Weekly Report (February 9, 1990), Centers for Disease Control and Prevention.
Impacts and Issues
HSV-1 is a common infection that usually lies dormant in the body within the nervous system. It causes health problems mainly in immunocompromised people, although the infection may be triggered in anyone carrying the virus through stress or sunlight exposure. People without symptoms may easily pass on the infection to those who are more vulnerable, so anyone who has ever had an outbreak of cold sores should consider themselves infected with HIV-1 and should take extra care with hygiene. Although antiviral drugs can treat the symptoms of cold sores, lessening their duration, they do not cure the infection itself.
HSV-1 infection is occasionally life-threatening. Untreated, HSV-1 encephalitis has a mortality rate of 70 percent and requires intravenous acyclovir to bring the infection under control. Neonatal (newborn) HSV-1 infection, although rare, can have a mortality rate of 60 percent, since the infant immune system is incapable of fighting it. Babies who survive often have severe neurological problems. Although for many people HSV-1 infection is of little consequence, for those who are already vulnerable, it may be extremely serious.
See AlsoChickenpox (Varicella); CMV (Cytomegalovirus) Infection; Herpes Simplex 2 Virus; Shingles (Herpes Zoster) Infection.
BIBLIOGRAPHY
Books
Gates, Robert H. Infectious Disease Secrets. 2nd ed. Philadelphia: Hanley and Beltus, 2003.
Gillespie S., and K. Bamford. Medical Microbiology and Infection at a Glance. Malden, U.K.: Blackwell, 2000.
Wilson, Walter R., and Merle A. Sande. Current Diagnosis & Treatment in Infectious Diseases. New York: McGraw Hill, 2001.
Web Sites
Skin Care Guide Network. “Herpes Guide—From Cold Sores to Genital Herpes.” November 1, 2006. <http://www.herpesguide.ca> (accessed February 3, 2007).
Susan Aldridge