Syphilis is a sexually transmitted infection caused by the bacterium Treponema pallidum. It is spread through direct contact with a syphilis sore, usually during vaginal, anal, or oral sex. Syphilis goes through various stages, and its contagiousness depends on the stage of infection.
Primary syphilis
The primary stage of syphilis is when it is most contagious. During this stage, syphilis bacteria multiply at the site of infection and cause one or more sores called chancres to develop. Chancres are the hallmark of primary syphilis.
Chancres are firm, round, and painless ulcers that develop at the syphilis bacteria entry site. Common locations include the penis, vulva, vagina, anus, rectum, lips, and mouth. Chancres contain large numbers of syphilis bacteria and are highly contagious.
A person is most contagious during the early phase of primary syphilis when the chancre is present. The chancre contains high concentrations of T. pallidum bacteria and contact with discharge from these sores can easily spread syphilis. Syphilis chancres are teeming with bacteria and any contact with a chancre can transmit syphilis.
On average, syphilis chancres appear around 21 days after infection, but can show anywhere from 10 to 90 days from exposure. Chancres last 3 to 6 weeks and usually heal regardless of treatment. Even after a chancre heals, syphilis remains in the body and can still be transmitted.
The approximate period of maximum infectiousness in primary syphilis is between 7-10 weeks. However, syphilis transmission can still occur if exposed to infectious discharges from lesions after they have healed.
Secondary syphilis
After primary syphilis, the disease moves into the secondary stage. At this point, the initial chancre has healed and the infection spreads through the bloodstream. Secondary syphilis is typically characterized by a non-itchy body rash, swollen lymph nodes, and patchy hair loss.
Secondary syphilis develops 2-10 weeks after the primary chancre heals, on average around 7 weeks. The rash often appears as rough, red or reddish brown spots on the palms of the hands and bottom of the feet. It can also develop on the arms, legs, chest, face, and trunk.
The rash can take many forms including maculopapular, macular, papular, pustular, and vesicular. A person is contagious during secondary syphilis when these skin and mucous membrane lesions contain treponemes.
However, secondary syphilis is considered less contagious than the primary stage. The risk of transmission varies based on the type of lesion, with wetter lesions being more infectious. The approximate period of contagiousness in secondary syphilis is between 4-10 weeks.
Latent syphilis
After secondary syphilis, the infection enters a latent or hidden stage. At this point, syphilis is no longer contagious. T. pallidum bacteria remain in the body during latent syphilis but are present in low numbers that cannot be transmitted sexually.
A person can remain in latent syphilis for years with no signs or symptoms before progressing to late syphilis. Latent syphilis is divided into early latent (less than 1 year after infection) and late latent (more than 1 year post-infection).
During the latent stage, syphilis is not contagious and cannot be transmitted sexually. However, a pregnant woman with latent syphilis can still spread the infection to her fetus.
Tertiary syphilis
The final stage is tertiary or late syphilis. At this point, syphilis can cause severe medical problems but is not contagious. After many years of latent infection, about one-third of people with untreated syphilis will progress to tertiary disease.
Tertiary syphilis develops around 3-15 years after initial infection and can affect the heart, brain, and other organs. This stage can cause life-threatening damage such as paralysis, blindness, dementia, and even death.
People with tertiary syphilis do not transmit the bacteria through sex and are no longer contagious. However, transmission during pregnancy is still possible at this stage if the mother has signs of active tertiary syphilis.
When is syphilis most infectious?
In summary, syphilis is often divided into contagious stages and non-contagious stages:
| Syphilis Stage | Contagious? |
|---|---|
| Primary | Yes, extremely contagious when sores are present |
| Secondary | Moderately contagious when mucous membrane lesions are present |
| Latent (early and late) | No, not contagious sexually during latency |
| Tertiary | No, not sexually contagious |
The most contagious period is during early-stage syphilis, when syphilis chancres or open sores are present on the external genitals, mouth, lips, fingers, or anus. Syphilis transmission occurs easily during vaginal, anal, or oral sexual contact with these infectious syphilis lesions.
Maximum infectiousness occurs when a syphilis chancre is present, typically 3-6 weeks after infection. Even after the chancre heals, syphilis can still be transmitted for a few more weeks. After the secondary rash resolves, syphilis is no longer contagious sexually in healthy adults.
Factors affecting syphilis transmission
Several factors can affect someone’s risk of acquiring or transmitting syphilis:
- Presence of syphilis sores or rash – Syphilis is most contagious when sores or lesions are present
- Stage of infection – Primary and secondary syphilis are more contagious than latent or tertiary
- Sexual behaviors that increase contact with sores such as oral, vaginal, and anal sex
- Sex without condoms or barriers to protect sores
- Multiple sex partners
- Presence of other STIs that cause sores like herpes or chancroid
- Being uncircumcised is linked to increased risk of syphilis transmission from women to men
Syphilis transmission through oral sex
Oral sex can transmit syphilis if mouth lesions caused by syphilis come into contact with a partner’s genitals, anus, lips, fingers, or mouth. Syphilis lesions commonly form on or around the lips and mouth.
During oral sex, syphilis can be spread through contact with infectious fluid from a chancre on the lips, tongue, or gums. Oral sex becomes riskier if skin inside the mouth is cut or scraped, allowing syphilis to enter the bloodstream more easily through the wound.
Using condoms, dental dams, or other barriers can reduce the risk of syphilis transmission through oral sex if they prevent contact with any sores. The risk of spreading syphilis through oral sex is highest when mouth sores are present.
Syphilis transmission through anal sex
Receptive anal sex carries a high risk of syphilis transmission if lesions around the anus, rectum, or genitals come into contact with an infected partner’s skin. Syphilis chancres often develop around the anus and rectum in those engaging in anal sex.
If syphilis lesions are present, their infectious fluid can enter the body through the thin anal tissue. Trauma from friction during anal intercourse may promote syphilis transmission by facilitating entry of treponemes through small tears in the skin.
Condoms are highly effective at reducing syphilis transmission during anal sex if they completely cover any sores. Proper condom use lowers the risk but does not eliminate it entirely. The riskiest period for transmission through anal sex is when active syphilis sores are present.
Syphilis transmission through vaginal sex
Vaginal sex with a partner who has a syphilis sore or rash easily transmits the infection. Syphilis bacteria can pass through intact mucous membranes including the surface of the vagina and cervix.
Chancre formation on the labia, clitoris, fourchette, and perineum is common in women with syphilis. Having syphilis lesions anywhere on the genitals makes transmission through vaginal sex highly likely if no barrier is used.
Barriers such as condoms, when used properly, decrease the risk of syphilis transmission through vaginal sex. But the highest risk of transmission remains when active syphilis sores are present in the genital region.
Mother-to-child transmission
Syphilis can pass from a pregnant woman to her fetus at any stage of infection. Congenital syphilis results from treponemes crossing the placenta during pregnancy. This can lead to miscarriage, stillbirth, birth defects, or infant death.
To prevent congenital syphilis, all women are recommended syphilis screening at the first prenatal care visit. Retesting in the 3rd trimester and at delivery is suggested for women at high risk or living in areas with high syphilis rates.
With early detection and penicillin treatment, congenital syphilis is largely preventable. However, up to 80% of infants with untreated congenital syphilis will be stillborn or die shortly after birth. Syphilis transmission to a fetus can have devastating consequences.
Syphilis transmission through kissing
Direct contact with syphilis lesions around the mouth can spread syphilis through kissing and other oral contact. While less common than transmission through sex, syphilis bacteria can be passed through deep kissing if active mouth sores are present.
However, casual contact like kissing without sores, sharing drinks, or using the same utensils will not transmit syphilis. Transmission risk through kissing rises if the infected person has mouth ulcers typical of primary or secondary syphilis stages.
Risk of syphilis transmission by stage
The timeline below summarizes the average period of contagiousness in each syphilis stage:
| Syphilis Stage | Transmission risk | Average contagious period |
|---|---|---|
| Primary | Extremely high when sores present | 7-10 weeks |
| Secondary | Moderate when rash present | 4-10 weeks |
| Latent (early and late) | None | Non-contagious |
| Tertiary | None | Non-contagious |
The average period of maximum infectiousness is 3-6 weeks during primary syphilis when an active chancre is present. In general, individuals are most contagious during the first year after syphilis infection.
Proper treatment can stop disease progression and prevent transmission. The most effective ways to avoid syphilis are abstinence, maintaining a mutually monogamous relationship with an uninfected partner, and using barriers to protect against skin-to-skin syphilis contact.
Conclusion
In summary, syphilis is most contagious during the primary and secondary stages when active sores and lesions are present. The highest transmission risk occurs when a syphilis chancre or multiple chancres are visible.
Primary syphilis with open genital sores remains the most infectious period due to the high concentration of syphilis bacteria in the chancre exudate. However, syphilis can still be transmitted after the chancre heals until treatment is completed.
Once past the secondary stage, individuals with latent or tertiary syphilis are not contagious sexually. Prompt diagnosis and treatment of syphilis are critical to stop transmission and prevent complications.
Using condoms, avoiding sex when sores are present, and limiting partners can also decrease syphilis spread. But the contagiousness of syphilis makes prevention challenging. Frequent testing and early treatment are vital, especially for sexually active individuals.
Syphilis transmission remains a public health concern due to substantial rates of infection in certain populations. Understanding when and how syphilis spreads empowers both healthcare professionals and individuals at risk to help combat this complex disease.