Syphilis is a sexually transmitted infection (STI) caused by the bacterium Treponema pallidum. This spirochete bacterium is highly infectious and can enter the body through mucous membranes or broken skin.¹ Once inside the body, Treponema pallidum can spread through the bloodstream and lymphatic system, leading to systemic infection. Despite being one of the oldest known sexually transmitted infections (STIs), syphilis remains a significant public health concern worldwide.² Understanding how syphilis is transmitted and the factors that increase the risk of infection is crucial for effective prevention and control. This article provides an in-depth exploration of the transmission pathways of syphilis and examines the various factors that contribute to increased susceptibility to this infection. 

Modes of transmission 

Sexual contact 

The most common mode of transmission of syphilis is through sexual contact. This includes vaginal, anal, and oral sex. The bacterium is present in the sores that occur during the primary stage of the infection, as well as in mucous patches and skin rashes that appear during the secondary stage.³ Contact with these infectious lesions during sexual activity facilitates the spread of the bacteria. 

Non-sexual contact 

While sexual contact is the primary transmission route, syphilis can also be transmitted through non-sexual means, although these are less common.¹ 

1. Congenital transmission (mother to fetus) 

Congenital syphilis occurs when an infected pregnant woman transmits the bacterium to her fetus through the placenta. This can lead to serious health complications for the newborn, including stillbirth, neonatal death, or severe congenital anomalies. 

2. Blood transfusion (rare) 

Transmission of syphilis through blood transfusion is extremely rare due to rigorous screening processes in blood donation centres. However, it remains a potential, albeit minimal, risk. 

Stages of syphilis and infectiousness 

Syphilis progresses through several stages, each with varying degrees of infectiousness.⁴ 

Primary stage 

The primary stage is characterised by the appearance of a single sore or multiple sores at the sites where the bacterium entered the body. These sores, known as chancres, are highly infectious. 

Secondary stage 

During the secondary stage, the infection manifests as skin rashes and mucous membrane lesions. These lesions are teeming with bacteria, making this stage highly contagious. 

Latent stage 

In the latent stage, the bacteria remain in the body without causing symptoms. While early latent syphilis (within the first year) can still be infectious, late latent syphilis is generally considered non-infectious. 

Tertiary stage 

The tertiary stage occurs in untreated syphilis cases and can result in severe health problems, including neurological and cardiovascular complications. By this stage, the infection is no longer considered contagious. 

Factors increasing the risk of infection 

Behavioral factors 

Engaging in sexual activity without the use of condoms significantly increases the risk of acquiring syphilis. Condoms are highly effective in reducing the transmission of syphilis when used correctly and consistently. 

Having multiple sexual partners increases the likelihood of exposure to syphilis. The more partners an individual has, the greater the risk of encountering someone who is infected. 

Substance abuse, particularly the use of drugs and alcohol, can impair judgment and lead to risky sexual behaviours. This includes having unprotected sex or engaging in sexual activity with multiple partners, thereby increasing the risk of syphilis infection. 

Biological factors 

The presence of other STIs, such as human immunodeficiency virus (HIV), can increase susceptibility to syphilis.¹ In particular, HIV compromises the immune system, making it easier for Treponema pallidum to establish an infection. 

Syphilis is more prevalent among certain age groups, particularly young adults aged 15-24 years. This demographic is often more sexually active and may engage in riskier sexual behaviours. 

Socioeconomic and cultural factors 

Limited access to healthcare services, including STIs screening and treatment, can increase the risk of syphilis infection. Individuals who do not have regular access to medical care are less likely to be tested and treated for syphilis. 

A lack of knowledge about syphilis, its transmission, and prevention can contribute to higher infection rates. Public health education plays a crucial role in raising awareness and promoting safer sexual practices. 

Stigma and discrimination associated with STIs can discourage individuals from seeking testing and treatment. This can lead to undiagnosed and untreated infections, which in turn increase the risk of transmission. 

Prevention and mitigation strategies 

Safe sexual practices 

Using condoms consistently and correctly during sexual activity is one of the most effective ways to prevent the transmission of syphilis.² Condoms act as a barrier, preventing the bacteria from being transmitted between partners. 

Regular screening for STIs, including syphilis, is essential for early detection and treatment. This is particularly important for individuals with multiple sexual partners or those in high-risk groups.⁵ 

Public health interventions 

Public health campaigns aimed at educating the public about syphilis, its symptoms, and prevention strategies are crucial. These campaigns can help reduce the stigma associated with STIs and encourage individuals to seek testing and treatment. 

Improving access to healthcare services, including affordable and confidential STI testing and treatment, is essential for controlling the spread of syphilis.³ Mobile clinics and community-based health programs can help reach underserved populations. 

Interventions tailored to high-risk groups, such as sex workers, can significantly reduce the incidence of syphilis. These interventions may include targeted education, free condom distribution, and accessible testing services. 

Personal responsibility 

Individuals diagnosed with syphilis have a responsibility to inform their sexual partners so that they can also seek testing and treatment. This helps prevent further transmission of the infection. 

Following prescribed treatment regimes is crucial for curing syphilis and preventing its spread. Penicillin is the preferred treatment for syphilis, and adherence to the full course of antibiotics is necessary to ensure the infection is completely eradicated. 

Conclusion

In summary, syphilis is a highly infectious STI caused by the bacterium Treponema pallidum. It is primarily transmitted through sexual contact, but can also be passed from mother to fetus and, rarely, through blood transfusion. The stages of syphilis– primary, secondary, latent, and tertiary– each have different levels of infectiousness, with the early stages being the most contagious. 

Several factors increase the risk of syphilis infection, including behavioural factors like unprotected sex and multiple sexual partners, biological factors such as the presence of other STIs, and socioeconomic factors like limited access to healthcare and lack of education. Addressing these risk factors through safe sexual practices, public health interventions, and personal responsibility is essential for preventing the spread of syphilis. 

Continued education and public health efforts are vital in raising awareness about syphilis and promoting prevention strategies. By understanding the transmission pathways and risk factors associated with syphilis, individuals can take proactive steps to protect themselves and others from this potentially serious infection. Safe sexual practices, regular STI screening, and adherence to treatment regimens are key components in the fight against syphilis.