Herpes: What Causes the Infection?

FROM THE LECTURE SERIES: An Introduction to Infectious Diseases

By Barry Fox, M.D., University of Wisconsin

The herpes virus family has over 100 members, but there are four main ones of clinical human significance. They not only cause acute infections but are never eliminated from the human body, surviving in a dormant state of hibernation inside host cells. Read on to learn more about the transmission and recurrence of this highly contagious virus.

Image showing the spread of germs from a person's breath.
Virus transmission mostly takes place via wet secretions like coughing and sneezing. (Image: Kateryna Kon/Shutterstock)

The Herpes Virus

Let’s consider an example of an 18-year-old college student who decides to go to Florida on spring break. Before going to Florida, she spent most of her time indoors studying for her exams, and once she arrives, she rushes to the beach.

She spends two days in the sun with minimal sun protection. Aside from the sunburn, she notices a painful sensation on the upper part of her lip, but there is nothing visible there. However, 24 hours later, a large blister appears at the site where the lip was having pain.

In her case, the diagnosis would be Herpes Type-1 infection. Herpes Simplex Virus I, abbreviated HSV-1, infects about 50 percent of the U.S. population by the age of 20. These lesions are highly contagious until they are fully healed in about a week. In the girl’s case, this was a viral reactivation triggered by sunlight.

The herpes virus family has over 100 members, but there are four main ones of clinical human significance: Herpes Simplex I and II; Epstein-Barr virus, which is responsible for infectious mononucleosis; Varicella-zoster responsible for chickenpox and shingles; and Cytomegalovirus, or CMV, responsible for some newborn infections and even birth defects.

Learn more about respiratory and brain infections.

Exposure to Herpes Viruses

Herpes Simplex I, while causing fever blisters, can also cause clinical disease at a wide variety of other anatomical sites. Herpes Type II is usually known as genital herpes.

Image of a girl with a blister near her lip.
Exposure to herpes causes an acute infection and the lesions are highly contagious until they are fully healed. (Image: Domaskina/Shutterstock)

During a person’s first exposure to herpes viruses, otherwise known as a primary infection, also called inoculation, herpes attacks the mucosal surface or moist mucous membrane sites. This permits the entry of the virus through the top layers of the skin.

Next, the virus invades the closest nerve endings. Local symptoms begin within a few days, with the appearance of blister type lesions superimposed on a red base.

Manifestation of Primary Herpes Infection

Sores in the mouth and severe sore throat with blisters are frequent manifestations of primary Herpes Type I infection, whereas fever blisters are the more frequent sign of recurrent disease.

Primary infection with herpes—either oral or genital—is usually associated with body-wide flu-like symptoms, fever, and malaise. The blisters with primary infection are very painful and can last up to ten days. The vesicles are usually grouped in a single anatomical site. However, if someone touches the sores, they can be spread to other body locations.

This is a transcript from the video series An Introduction to Infectious Diseases. Watch it now, on The Great Courses Plus.

Most Primary Herpes Infections Are Asymptomatic

It comes as a surprise that, even with all the severe symptoms, most primary herpes infections are asymptomatic—no symptoms. Analysis of blood from the general population demonstrates that only 20 to 25 percent of individuals with Herpes Type I immunity, and 10 to 20 percent of those with Herpes Type II, remember having a history of blisters at the site of infection.

Hence, patients with known Herpes Type I or II infection represent only the tip of the iceberg. This has tremendous implications for virus transmission since the herpes virus can be shed without clinical signs of disease and can lead to stealthy transmission via contact with secretions.

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What Causes Herpes to Recur?

Once the herpes primary infection has occurred, the virus survives in a dormant or hibernating state inside host cells and can reactivate at a later time. The frequency and severity of reactivation is determined by many factors.

Precipitating factors for herpes recurrences include fever, menstruation, emotional stress, trauma to the area of primary infection, and exposure to sunlight.

Symptoms of Herpes Recurrence

In contrast to primary herpes, recurrences are usually not associated with body-wide symptoms. Those afflicted with herpes can usually tell in advance when an episode is forthcoming.

Prodromal symptoms or early warning symptoms are common before a reactivation event. These symptoms include tingling, itching, pain, and burning. The prodromal symptoms usually start one to three days prior to the appearance of the first blisters.

Although the specific triggers for an outbreak can be predictable for an individual, and vesicles tend to recur at the same site for an individual, the pattern and recurrences vary from person to person.

Recurrent episodes are shorter than the primary episode and typically last five to seven days. Although 25 percent of individuals have recurrences as frequently as once a month, another quarter is as infrequent as only twice per year.

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Types of Herpes Infection

Herpetic Whitlow is a herpes condition that occurs when the virus infects the finger. This occurs by inoculation of the virus through a break in the finger skin by touching active vesicles of the mouth.

A sketch showing a person affected by Bell's Palsy.
Bell’s Palsy is a neurological condition that results in the drooping of one side of a person’s face. (Image: corbac40/Shutterstock)

Outbreaks of Herpes Type I skin infections have also occurred among wrestlers and rugby players because of the exposure of their skin to the sweat and saliva of other players. This type of skin infection is referred to as ‘herpes gladiatorum’.

There are a variety of other neurological syndromes that have been linked to herpes infection, including Viral Meningitis that means inflammation around the brain and the spinal cord.

Bell’s Palsy is a neurological condition where there is temporary damage to the facial nerves, causing one side of the face to droop, also caused by herpes.

Unlike most viral illnesses, there actually are antiviral drugs that can be used for treatment and prevention. Since these are all DNA viruses, these medications can target DNA polymerase. Acyclovir is the most well-known antiviral medication used for herpes, chickenpox, and shingles.

Common Questions about the Herpes Virus

Q: What factors may cause herpes recurrences?

Factors for herpes recurrences include fever, menstruation, emotional stress, trauma to the area of primary infection, and exposure to sunlight.

Q: What are the four main herpes viruses of clinical human significance.

The four main herpes viruses of clinical human significance are Herpes Simplex I and II, Epstein-Barr virus, Varicella-Zoster, and Cytomegalovirus or CMV.

Q: What is Bell’s Palsy?

Bell’s Palsy is a neurological condition where there is temporary damage to the facial nerves, causing one side of the face to droop.

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