What health complications can occur due to an untreated syphilis infection?

Syphilis a sexually transmitted disease caused by the bacterium Treponema pallidum subspecies pallidum. It has been called “The Great Pretender”, as symptoms can resemble other diseases. If syphilis is untreated it can cause serious health complications. There are distinct stages of a syphilis infection, known as primary, secondary, latent, and tertiary.

Primary stage
A skin lesion, called a chancre, is the first sign of a syphilis infection. Chancres appear at the location where syphilis entered the body anytime from 10-90 days after infection, with an average onset of 21 days post-infection (1). Chancres last for three to six weeks and heal whether or not treatment is received. Individuals in this stage are very infectious. If untreated, the infection progresses to the secondary stage (2).

Secondary stage
Skin rashes and/or lesions in the mouth, vagina, or anus occur during the secondary stage of infection. These may appear when the primary chancre is healing or several weeks after it has healed. Additional symptoms in the secondary stage can include fever, sore throat, hair loss, weight loss, swollen lymph glands, headaches, muscle aches, and fatigue. Individuals in this stage are infectious. Like the primary symptoms, secondary symptoms will also disappear whether or not treatment is received. However, the syphilis infection will progress to the latent stage if adequate treatment does not occur (2).

Latent stage
There are no visible signs or symptoms of syphilis during the latent (hidden) stage. However, syphilis-causing bacteria (T. pallidum) are still present. The latent stage can last for many years, with 15-40% of untreated individuals developing tertiary syphilis (3). Individuals in the early latent stage (less than 1-2 years after the original infection) may be infectious, but individuals in the late latent stage are generally not infectious.

Tertiary stage
In rare cases, the latent stage progresses to a potentially fatal tertiary stage. This can occur 10-30 years or more after acquiring a syphilis infection. Multiple different organ systems can be affected including the brain, nerves, eyes, heart, liver, bones, and joints. The associated symptoms vary depending on the affected body parts. Individuals with tertiary syphilis are not infectious (1).

Gummatous syphilis or later benign syphilis can occur in the tertiary stage. It is characterized by soft, tumor-like balls of inflammation, which typically affect the skin, bone, and liver. Cardiovascular syphilis is a relatively common complication of tertiary syphilis, where the heart tissue is affected (1).

Neurosyphilis and ocular syphilis
At any stage of infection, T. pallidum can invade the nervous system causing neurosyphilis, or the eyes causing ocular syphilis. Neurosyphilis symptoms can include headaches, paralysis, dementia, sensory deficits, and altered behavior. Ocular syphilis can cause vision changes, decreased visual acuity, and blindness (2). 

Congenital syphilis
Syphilis during pregnancy is associated with miscarriage, stillbirth, or infant death shortly after delivery in up to 40% of cases. Congenital syphilis occurs when an infected pregnant woman passes syphilis to her baby during pregnancy. If an infected infant is not treated immediately, serious health complications can occur, including enlargement of the liver and spleen, rashes, fever, neurosyphilis, lung inflammation (4), developmental delays, seizures, and other fatal complications (5).

References
1. Kent ME & Romanelli F (2008). Reexamining syphilis: an update on epidemiology, clinical manifestations, and management. Ann Pharmacother, 42 (2), 226-236.
2. Syphilis – CDC Fact Sheet (Detailed). (2017, January). https://www.cdc.gov/std/syphilis/stdfact-syphilis-detailed.htm
3. Peeling RW, et al. (2017). Syphilis. Nat Rev Dis Primers, 3 (17073).
4. Woods CR. (2009). Congenital syphilis-persisting pestilence. Pediatr Infect Dis J , 28 (6), 536-537.
5. Sexually Transmitted Diseases Treatment Guidelines, 2015. (2015). MMWR, 64 (RR-3).