Why can syphilis spread especially easily during its primary and secondary stages?

Syphilis spreads easily during its primary and secondary stages because these phases are characterized by the presence of open, infectious sores on the skin or mucous membranes.1

During the primary stage, the infection manifests as a chancre—a painless ulcer that contains the spirochete bacterium Treponema pallidum. The secondary stage often involves the development of rashes and other lesions. Because the causative bacteria require moisture to survive, the continuous presence of these open, moist lesions provides a direct pathway for the spirochetes to be transferred from an infected person to others through physical contact, most commonly during sexual intercourse.2134

It is important to recognize that because these early symptoms can sometimes be painless or go unnoticed, individuals may unknowingly transmit the disease. Seeking prompt medical evaluation and treatment with penicillin is essential to prevent the progression of the disease and to protect the health of others.2143