One of the most common sexually transmitted diseases (STDs) is herpes, which affects an estimated 1 out of 6 Americans between the ages of 14 and 49. Herpes is caused by a virus, and one reason that it’s so widespread is that the herpesvirus is ancient. Prehistoric, even — dinosaurs are thought to have been infected by herpesviruses! The Herpesviridae family is huge, with at least 100 members infecting mammals, birds, reptiles, bony fish, amphibians, and oysters.

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Herpes drugs from the acyclovir family physically block herpes DNA from replicating — which is pretty amazing!

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Humans can suffer from both oral herpes and genital herpes, which are caused by two types of the herpes simplex virus (HSV-1 and HSV-2). Recent genetic analysis reveals that the virus that causes cold sores, HSV-1, has been evolving with us since before we were Homo sapiens, diverging from the viruses that infected our common ancestors 6 million years ago. Interestingly, we didn’t acquire HSV-2 — which mostly causes genital herpes — until our Homo erectus ancestors caught it from early chimpanzees 1.6 million years ago, well before the emergence of modern Homo sapiens around 200,000 years ago.

Most people know what the virus does — genital herpes can involve blisters, pain, and itching — but most people don’t know how the virus works. Luckily, scientists have uncovered a lot of the virus’ secrets — which has allowed them to develop some pretty effective drugs that we can use to foil herpes’ plans.

How the Herpes Virus Works

Genital herpes is transmitted by sexual contact. It can be passed to or from the mouth, the genital region, or the anal region — via oral, anal, or vaginal sex, or by skin-to-skin contact without penetration. Once inside its new human home, the virus does what viruses do: It hijacks the host’s cells and tricks them into manufacturing copies of new viruses.

After entering the host’s body, through a tear in the skin or through the mucous membrane, the virus begins a journey up the sensory neurons — the nerves that we use to perceive pain and other physical sensations. It then comes to a cluster of nerves called a “ganglion,” where the viruses shoot their DNA into the cells’ nuclei, integrating their DNA with that of their hosts. At that time, they establish latency: A few days after infection, virus particles can’t be detected, and all that remains are the herpes genes, which have silently slipped into the DNA of infected cells, waiting to be reactivated.

Herpes simplex virus particles inside a host cell. Image: Public Health Image Library, CDC

We’re not sure exactly what triggers a latent herpes infection to be reactivated, but it’s thought that illness, stress, surgical trauma, and steroidal medications can increase risk. When an infection flares back up, the viral genes are activated and our infected cells produce viral proteins. These proteins eventually form shells that each encapsulate a piece of viral DNA — these are the actual infectious particles that can deliver the viral DNA to another person.

During this time, the human in whose body these molecular machinations are all taking place might experience the unpleasant symptoms associated with herpes. Or this person might not have any symptoms at all. The severity of a reactivation has to do with the host’s immune system, the virulence of the viral strain, and how much replicating virus is around. During an outbreak, new copies of the virus are being manufactured, and the host can pass the infection onto someone else. This is because, when the virus emerges from dormancy, it travels back down the nerve toward the skin’s surface, where it might come into contact with a new host.

When the virus returns to dormancy, it retreats to the nerve ganglia, where it might remain latent, or might be retriggered to begin the cycle anew. Many people with genital herpes infections experience a decrease in frequency of outbreaks over time, and sometimes they stop altogether. Some people, however, experience recurring herpes outbreaks throughout their lives.

How Herpes Medications Thwart the Virus

While they’re not cures, the antiviral medications we use to fight herpes work quite well, especially when they are started as soon as possible after symptoms appear. The acyclovir family of herpes drugs includes acyclovir (Zovirax) and its cousins valacyclovir (Valtrex) and famciclovir (Famvir). These drugs have been used for years to fight herpesvirus infections.

The acyclovir family of drugs work by stopping herpes DNA synthesis in its tracks. When herpes DNA is replicating within an infected cell, the cell starts producing viral enzymes. When the herpes drug enters the cell, these enzymes physically change the drug’s molecular structure just enough to enable it to attach to a strand of herpes DNA as it is being copied. At this point, the process comes to a grinding halt, because the building blocks of DNA (the A’s, T’s, C’s, and G’s you might remember from your last biology class) aren’t able to attach to the herpes drug molecules. The acyclovir family of herpes drugs physically block the DNA from replicating — which is pretty amazing! Even cooler is that these drugs have no effect in cells that aren’t infected with herpes, because its ability to attach to DNA is triggered by viral enzymes that are only present in infected cells.

Some people take these drugs for five to 10 days when they experience symptoms, and the medication reduces the pain and speeds the healing of sores. Some people, especially those who are more prone to outbreaks, might be advised by a health-care provider to take herpes medications continuously for longer periods of time in order to suppress those outbreaks.

Drug resistance is possible, and when that happens, the drug can’t enter your DNA to block viral gene expression. For best results, take the medications as prescribed — don’t stop taking them too early, don’t skip doses, and don’t take a double dose if you do accidentally skip a dose. These drugs can also cause side effects, such as upset stomach, vomiting, diarrhea, and fatigue — if they don’t go away on their own, see a health care provider. Other side effects are considered serious enough that you should see a health care provider immediately if you experience them, including swelling, difficulty breathing or swallowing, fast heartbeat, blood in the urine or diarrhea, and more. However, most people take these drugs with no problems.

While herpes drugs from the acyclovir family can help suppress herpes outbreaks, reduce symptoms during outbreaks, speed healing, and lower the risk of transmitting herpes to a sexual partner, they aren’t a cure for herpes. Those taking them still run the risk of experiencing symptoms and passing the infection to a partner — but that risk is reduced when the herpes drugs are taken as directed.

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