The Facts
Infectious mononucleosis (called "mono" for short) is caused by
the Epstein-Barr virus (EBV), a virus that affects nearly everybody at
some point. The disease is sometimes known as glandular fever, because
it causes lymph glands to swell up. It's also called the "kissing disease"
because kissing is a common method of transmission.
Before the age of five, 50% of us are infected by EBV. By the age of
40, 90% of us are infected. Once you've caught the virus, it never really goes
away. However, it can only cause symptoms in healthy people when it's still
new in the body. After that it's kept in check by the immune system, though
never completely eradicated.
Of course, nowhere near 90% of the population has suffered from mononucleosis.
Half of all people are infected with EBV before age five, and this age group
hardly ever has symptoms beyond occasional mild tonsillitis. Unless their immune
system collapses, they will never have mononucleosis. In the 5-to-30-year age
group, most studies have found that about 10% of people with EBV get the symptoms
of mononucleosis. The exception is college students, who have rates of around
1 case for every 2 infections, several times higher than non-college students
of the same age.
There are rare cases of mononucleosis occurring in older people, but usually
the ones affected have weakened immune systems. Older people will usually have
been infected much earlier in their lives. Such cases tend to be severe but
not deadly.
In recent years, a link has been postulated between Epstein-Barr virus and
chronic fatigue syndrome, but the latest studies seem to refute that. There
is, however, a long-standing link with Burkitt's lymphoma, a cancer that
occurs mostly in central Africa. EBV is one of a very few viruses known to be
capable of causing cancer.
There's also a weak link with nose and throat cancer. The small minority of
people who don't carry the Epstein-Barr virus have a lower-than-average chance
of developing this cancer.