What are cold sores?|
Also known as fever blisters, herpes labialis, herpes febrilis, herpes facialis and orofacial herpes.
What causes the disease?
Cold sores are caused by a virus which is known as 'Herpes Simplex'. There are two different types of Herpes Simplex Virus (HSV); HSV-1 and HSV-2. HSV-1 is thought to cause cold sores whereas HSV-2 causes genital herpes ( the sexually transmitted disease).
Viral infections are very different from bacterial infections. When someone becomes infected with HSV it gets into the cells (the basic building blocks which make up our body) of the lips and mouth. It then takes over these cells, using them as a 'factory' to produce more viral particles. In this way the virus replicates and is able to take over / infect nearby lip cells as well.
HSV infection is first acquired from exposure to people who have the infection. So kissing or facial contact is the primary means of spreading infection. Medical studies suggest that most HSV-1 infections occur in childhood from kissing infected parents. Poor hygiene and crowded living conditions increase the risk of HSV-1 infection. People don't have to have cold sores to be infectious either. Sometimes people can have the virus in their lips and be highly infectious without actually having cold sores at the time.
A characteristic of the HSV-1 is it's ability to cause latent or dormant infection. After the first episode of being infected with the virus (known as the primary infection) the HSV travels up the nerves which go to the infected area. The virus then lies in a dormant state (ie. hibernating) until it is reactivated. When reactivation occurs the virus travels back down the nerves and causes infection again. It is this reactivation of infection which causes cold sores. When the cold sore heals the virus goes back up the nerves to lie dormant again. So this process of hibernating and then reactivating can go on indefinitely. That's why people can get rid of their cold sores only to have them return again. The nerves are not damaged by the virus.
There are a number of factors which can lead to reactivation of disease. These include sun exposure, damage to the lips and mouth emotional stress, fatigue and the presence of other infections (eg. having a 'cold'). Patients who have a weakened immune system (ie. their body's defences are weaker than normal) also have an increased rate of recurrence in cold sores. HIV infection, cancer, bone marrow disorders and some drugs (eg. steroids, chemotherapy) can cause weakened immunity.
- Cold sores are estimated to affect 15-40% of people. Some studies have also shown that over 85% of people have been exposed to HSV-1 ( ie. their bodies defences have made antibodies to fight against HSV-1 although they may not have cold sores).
- The number of recurrences per year varies widely although the average is 3-4.
- Cold sores occur all over the world and males and females are equally affected.
- It is thought that cold sores occur more commonly in the Winter months.
- Acute (primary) infection is most often seen in children and young adults.
Primary infection with HSV
This usually occurs in children. They may experience a sore mouth and throat with fever and inflamed gums. Following this small blisters or ulcers can form in the mouth or on the lips. Swollen lymph glands in the neck (felt underneath the back of the jaw) are also common. Infants can be extremely irritable and refuse to eat and sleep. These symptoms are often misinterpreted as being due to a 'cold'.
In adults the symptoms of primary infection are tiredness, fever, headache and ulcers on the gums, lips and tongue.
Frequently the symptoms of the primary infection are very mild. Often people can develop cold sores and have no recollection of a primary infection.
Cold Sores (recurrent HSV-1 infection)<