Glandular fever is caused by the Epstein-Barr virus (EBV). EBV is most often spread through the saliva of someone who carries the infection.
For example, it can be spread through:
- kissing – glandular fever is sometimes referred to as the "kissing disease"
- sharing food and drinks
- sharing toothbrushes
- exposure to coughs and sneezes
Small children may be infected by chewing toys that have been contaminated with the virus.
When you come into contact with infected saliva, the virus can infect the cells on the lining of your throat.
The infection is then passed into your white blood cells before spreading through the lymphatic system.
This is a series of glands (nodes) found throughout your body that allows many of the cells that your immune system needs to travel around the body.
After the infection has passed, people develop lifelong immunity to the virus and most won't develop symptoms again.
Many people are first exposed to EBV during childhood, when the infection causes few symptoms and often goes unrecognised before it eventually passes.
Young adults may be most at risk of glandular fever because they might not have been exposed to the virus when they were younger, and the infection tends to produce more severe symptoms when you're older.
Not everyone who can pass on EBV will have symptoms themselves. These are known as asymptomatic carriers.
Some people can have the virus in their saliva for a few months after recovering from glandular fever, and may continue to have the virus in their saliva on and off for years.
This is because the virus remains inactive in the body for the rest of your life after you have been exposed to it. For most people, the inactive virus won't cause any symptoms.
However, there is a chance of the virus periodically becoming reactivated, which may mean it re-enters the saliva. This reactivation may be without any symptoms, or it may cause symptoms to recur for a short time.