The human is evidently the sole natural host and source of T. pallidum. It is an extremely fastidious and sensitive bacterium that cannot survive for long outside the host, being rapidly destroyed by heat, drying disinfectants, soap, high oxygen tension and pH change. It survives a few minutes to hours when protected by body secretion and about 34 hours in stored blood.
Syphilis infection is usually acquired by sexual contact with infected individuals, and is commonest in the most sexually active age group of 15 – 30 yr olds. Rarely, syphilis has been acquired by transfusion of infected fresh human blood.
The eariliest indication of syphilis infection, after an incubation period of nine days to three months, is the appearance of a hard canker at the site of inoculation.
The canker begins as a small, red, hard, bumps that enlarges and breaks down, leaving a shallow crater with firm margins. The cankers heals spontaneously without scarring in three to six weeks, but this healing is deceptive, because the spirochete has escaped into the circulation and is entering a period tremendous activity.
About healing of canker in 3 – 6 months, the second stage appears. By then, many systems of the body have been invaded and the sympotoms are more profuse and intense. Initially there is fever, headache and sore throat, followed by lymphadenopathy and a peculiar red or brown rash that breaks out on all skin surface, including the palms and the soles. The major complications develop in the bones, hair follicles, joints, liver, eyes, brain and kidneys.