Herpes Simplex Virus: Transmission and Transmissibility
Herpes Simplex Virus (HSV) invades the body through skin and mucous membranes. Then virus invade the nervous system, establishes latent (dormant) infection in nerve cell ganglia nearest to the original site of infection. HSV is a chronic infection, with periods of asymptomatic viral shedding and unpredictable recurrences of blister-like lesions.
There are two types of HSV: Herpes simplex virus type 1 (HSV-1) and Herpes simplex virus type 2 (HSV-2).
HSV-1 is usually the cause of oral infection. Initial oral infection with HSV-1 may cause gingivostomatitis (mainly in children) and herpetic pharyngitis (mainly in adolescents and adults). Recurrent infection causes herpes labialis (or cold sores) . HSV-1 infects about 80% of the U.S. population and usually appears on the lips in cold sores.
Most cases of genital herpes are caused by HSV-2. Genital herpes is a sexually transmitted disease.
While genital HSV can be a frustrating and painful condition, in general the virus is less a medical problem than a social problem. For most people genital herpes is no more dangerous than cold sores.
Many people with genital herpes don't know they have it, and are unaware they may be spreading virus to others. Many have no symptoms or mistake their symptoms for something else, such as jock itch, insect bites, hemorrhoids, yeast infections, razor burn, or allergies.
The main difference between the two types of herpes virus is in where they typically establish latency (lie dormant) in the body -- their "site of preference."
Nevertheless, either type can infect both oral and genital areas. Genital herpes can be caused by both HSV-1 and HSV-2. And signs and symptoms of initial genital herpes caused by HSV-1 or HSV-2 are indistinguishable. However, subsequent recurrences are more frequent with HSV-2.
Oral HSV-2 although possible, occurs very rarely.
How to distinguish between HSV-1 and HSV- 2?
Either type of herpes virus can invade both oral genital areas of the body. Only serologic tests for herpes antibodies to viral glycoprotein G allow to definitely distinguish between HSV-1 and HSV- 2.
HSV-1 reactivates more frequently in the oral than in the genital area. Similarly, for HSV-2, reactivation in the genital area is 8 to 10 times more frequent than oral reactivation.
HSV-2 strains shut off host cellular protein synthesis more rapidly and more completely than do HSV-1 strains.
HSV-1 is the most common cause of sporadic, viral encephalitis. HSV-2 is the most common cause of recurrent, benign lymphocytic meningitis.
Primary oral infection with HSV-1 usually causes gingivostomatitis (mainly in children) and herpetic pharyngitis (mainly in adolescents and adults).
Primary genital herpes can be caused by both HSV-1 and HSV-2. Signs and symptoms of the first genital herpes episode caused by both HSV-1 and HSV-2 are indistinguishable. However, recurrences are more frequent with HSV-2. The clinical courses of first-episode genital herpes among patients with HSV-1 and HSV-2 infections are identical. However, the 12-month recurrence rates among patients with first episode are 90% for HSV-2 and 55% for HSV-1 infection.
Herpes virus is spread only through direct contact of broken (abraded) skin and mucous membranes with the contagious area (an infected person's herpes lesions, mucosal surfaces, genital or oral secretions). Mucous membranes of the mouth and genital area are the most vulnerable sites.
Broken areas of skin and intact mucous membranes permit entry of the virus ("inoculation") and initiation of its replication in cells of the epidermis and dermis.
HSV can be transmitted through the following activities:
The herpes virus is quite fragile. HSV does not survive outside the body for more than about 10 seconds, and although it can survive for slightly longer in warm, moist conditions, it dies very quickly once exposed to the air. Transmission through inanimate objects such as toilet seats is unlikely. Precautions include not sharing towels, underwear, or other objects that come into contact with genital lesions.
Note: Humans are the only natural reservoir for transmission of HSV . This virus is not transmitted to humans by animals.
Genital herpes is not hereditary. The virus has no effect on fertility and is not transmitted via men's sperm or women's ova.
It is more common for oral HSV-1 to be transmitted to the genitals through oral sex, than it is for HSV-2 to be transmitted to the mouth. If a person has oral herpes (cold sores), and performs oral sex on the partner, it is possible for that person to transmit the virus to the genitals from this action, and vice versa.
If you already have certain HSV type then acquisition of another type of HSV is more difficult (though certainly possible). This is because either type, contracted orally or genitally, causes the body to produce antibodies, some of which are active against both HSV-1 and HSV-2. This acquired immune response gives some limited protection if the body encounters a second type. When a person with a prior HSV infection does contract the second type, the first episode tends to be less severe than when no prior antibodies are present.
Almost all HSV-2 is encountered after childhood, when people become sexually active. Those who have a prior infection with HSV-1 have an acquired immune response that lowers (though doesn't eliminate) the risk of acquiring HSV-2. According to the research , previous oral HSV-1 infection reduces the acquisition of subsequent HSV-2 infection by 40%.
Prior oral HSV-1 infection lowers the risk of acquiring genital HSV-1 infection even further. Studies show that genital HSV-1 infections almost always occur in people who have no prior infection with HSV of either type . In the absence of prior oral infection, however, HSV-1 spreads easily to the genital area, usually through oral sex. In some countries, such as Japan and parts of Great Britain, genital HSV-1 is as common as genital HSV-2, or more common.
If you have genital HSV-1 and your partner has genital HSV-2 and you have unprotected sex, there is a small but real risk that you will get HSV-2, resulting in more outbreaks and more shedding. There are documented cases where a person acquires HSV-2 after a prior genital HSV-1 infection. It doesn't happen often, but it does happen. However, it's very unlikely that your partner will get genital HSV-1 from you. It's possible, but very unusual.
If your partner has genital HSV-2 and you perform oral sex on him or her, there is a very low risk that you will get oral HSV-2. According to one study, almost 100% of recognizable HSV-2 infection is genital (Nahmias, Scandinavian Journal of Infectious Diseases Supplement, 1990). One reason is that most adults are already infected with HSV-1 orally, which provides some immunity against infection with HSV-2. Another reason is that oral HSV-2 rarely reactivates, so even if an infection does exist, no one knows .
If you acquire genital HSV-1 through oral sex, you can spread the virus to a partner through genital sex. But probably it is not as easily as it was spread through oral sex. The main reason is that the virus reactivates and sheds less often outside its site of preference. Only about 25% of people with genital HSV- 1 shed virus at all in the absence of symptoms, while 55% of people with HSV-2 do . However, transmission of genital HSV-1 during asymptomatic shedding has been well documented. In other words, genital HSV-1 can be spread through genital sex, even when there are no symptoms.
When Herpes virus is most likely to be transmitted
Likelihood of HSV transmission
Individuals who reactivate the virus without visible symptoms still release the virus in the oral or genital tract. Asymptomatic viral shedders are at risk of unknowingly spreading the virus to partners.
Duration of infection
Frequency of recurrences
Neural tissue transport of herpes simplex virus results in life-long latent infection. HSV remain in the body for life, hidden in a dormant state inside nerve cells.
The virus escapes the usual immune response by penetrating nerve fibres. As the immune system moves in to control the infection, the virus conceals itself within nerve cells. The virus is carried to the nerve "cell body" in a swelling called a ganglion located close to the spinal cord. When it reaches the cell body, the viral DNA is added alongside the nerve cell's own DNA in the nucleus. It remains there, hidden within the nerve cell and in an inactive state, for the lifetime of the infected individual.
Retrograde transport through adjacent neural tissue to sensory ganglia leads to lifelong latent infection. Once reactivated, the virus is transported by the neuron back to the epithelium, where more replication occurs, and another outbreak ensues.
Symptoms of genital herpes can vary in appearance and intensity. Some people have no symptoms or such mild symptoms that they don't suspect they have an infection. For others, the first episode of herpes (primary infection) can cause one or more very painful lesions to erupt on the skin.
Genital herpes lesions usually appear within 2 to 10 days after being exposed to the virus, and can last from two to four weeks. First to appear are small red bumps, which develop into blisters. Then the blisters become open sores, which later dry up, crust over, and heal without leaving a scar. Symptoms experienced during lesion formation include: swollen lymph glands, headaches, fever or general malaise, pain, muscle aches.
After the initial outbreak, the virus moves away from the skin surface and travels along the nerve pathways to nerve roots at the base of the spine and goes into an inactive phase. The virus may reactivate and lesions reappear at the same site as the original infection, but usually are much less severe. If the infection is caused by HSV-1, the (first year) recurrence rate is 50%. The HSV-2 recurrence rate during first year is 80-90%.
Researchers don't know why recurrences happen, or why their frequency and severity vary.
Frequency of herpes outbreaks depends on three factors:
HSV-2 infection in the oral area very rarely causes problems. Oral HSV-2 infections are very rare. But even when an infection occurs, recurrent outbreaks are extremely rare. In one study (Lafferty et al., New England Journal of Medicine, 1987), oral HSV-2 recurred an average of 0.01 times a year in newly infected people.
Some triggers of outbreaks:
More on herpes:
Created: August 18, 2006