Syphilis Overview and Biology

Syphilis: An Overview

Syphilis is a chronic bacterial infection caused by the spirochete Treponema pallidum subsp. pallidum that is endemic in low-income countries and occurs at lower rates in high-income countries. The disease is primarily spread through sexual contact with active primary or secondary lesions, and it can also be transmitted vertically from mother to fetus in pregnant women.

Biology of T. pallidum

T. pallidum has an unusually small genome and lacks genes that encode many metabolic functions and classical virulence factors, making it extremely sensitive to environmental conditions. Despite these challenges, it is highly infectious and can survive for decades in the untreated host. The organism has an unusual capacity for invasion of the central nervous system (CNS) and placenta, and its genomic sequences are used to understand its biology.

Stages of Syphilis

Syphilis is typically divided into four stages: primary, secondary, latent, and tertiary.

1. Primary Syphilis: Characterized by a single ulcer (chancre) or multiple lesions on the genitals or other body sites. These lesions are typically painless and resolve spontaneously after 6-8 weeks.
2. Secondary Syphilis: Occurs 6-8 weeks after primary syphilis and is characterized by fever, headache, maculopapular rash on the trunk, and involvement of the palms and soles.
3. Latent Syphilis: The latent phase can last for many years. Patients in the first 1-2 years of latency are still considered infectious.
4. Tertiary Syphilis: Historical literature suggests that 15-40% of untreated individuals will develop tertiary syphilis, which can manifest as destructive cardiac or neurological conditions, severe skin or visceral lesions (gummas), or bony involvement. However, recent data suggest that the prevalence of tertiary syphilis may be less common today due to the wide use of antibiotics.

Transmission and Prevalence

Syphilis is primarily transmitted through sexual contact with active primary or secondary lesions. It can also be transmitted vertically from mother to fetus in pregnant women. The prevalence of syphilis is highest in low-income countries, and its incidence has declined in high-income countries since the introduction of penicillin.

Current Challenges and Research

Current challenges in syphilis research include the organism's ability to evade the host's immune system, its high sensitivity to environmental conditions, and the emergence of macrolide resistance. Research efforts are focused on understanding T. pallidum's biology and pathogenesis, as well as developing a syphilis vaccine, which would have a significant positive impact on global health.