Swollen lymph nodes can crop up when your body is fighting many different kinds of infection or illness. First, a little anatomy lesson to clarify why lymph nodes are so prone to bulging.
However, very occasionally, swollen lymph nodes can be a sign of inflammation deeper inside the body, or more rarely, a sign of cancer, but in this case they are usually much larger than a pea.
The name comes from the symptoms it causes - painful, swollen lymph nodes or 'buboes' in the groin or armpit. From 2010 to 2015 there were 3,248 cases reported worldwide, including 584 deaths.