At what stage is syphilis most contagious? Infection can be detected 10 days after high-risk behavior!

Author: Wang Linghang, Chief Physician, Beijing Ditan Hospital, Capital Medical University

Reviewer: Zhang Yu, researcher at Chinese Center for Disease Control and Prevention

Syphilis is a sexually transmitted disease caused by Treponema pallidum infection, which is mainly transmitted through sexual contact, mother-to-child transmission, etc. Depending on the course of the disease, it is divided into early syphilis and late syphilis.

1. How are early syphilis and late syphilis divided?

Syphilis is generally divided into three stages.

The first stage is mainly characterized by characteristic lesions at the site of Treponema pallidum invasion, such as the appearance of a chancre in the coronal sulcus of the male penis. This type of chancre is often painless, and the ulcer is 1-2 cm in size. Chancres tend to heal on their own and will heal on their own without treatment in 3-6 weeks. The body's immune system suppresses Treponema pallidum. Although it cannot be completely eliminated, it can be controlled, so the ulcer will slowly heal.

Figure 1 Original copyright image, no permission to reprint

Because there is no specific treatment, the Treponema pallidum is not completely eliminated from the body and remains dormant. After a few weeks or half a year, it will be activated again and affect the whole body, such as skin and mucous membrane lesions and syphilitic rash, especially on the palms and soles. This stage belongs to the secondary stage and the syphilitic rash can be cured without treatment.

Figure 2 Original copyright image, no permission to reprint

After the second stage, there are still a small amount of Treponema pallidum in the body, which will cause a mild inflammatory reaction accompanied by a granulomatous reaction. The body's immune system wants to eliminate this pathogen, and it reacts to it, but the force is not strong enough, which will still affect the organ function and enter the third stage. Tertiary syphilis has various manifestations such as gumma, syphilitic heart disease, and neurosyphilis. Neurosyphilis includes ocular syphilis, meningeal vascular disease, and cranial nerve damage, which can cause facial paralysis, sudden deafness, etc.

The incubation period from the onset of Treponema pallidum infection to the appearance of chancre is generally 10-90 days, and the chancre generally heals itself in 3-6 weeks. After the chancre improves, about 25% will progress to secondary syphilis, and it takes several weeks to half a year from the end of the first stage to the second stage. Primary and secondary syphilis generally last within a year and are collectively referred to as early syphilis. If it lasts more than a year, it is called late syphilis.

2. At what stage is syphilis most contagious?

The infectiousness of syphilis is strong at first and weaker later. Latent syphilis, primary syphilis and secondary syphilis are all highly contagious.

The so-called latent period is when the Treponema pallidum has invaded the body, but no corresponding symptoms have appeared, and no examination has been done to confirm it; or after one period, it enters a period without symptoms, which is collectively referred to as the latent period or clinical latent period. As long as the body has been infected with syphilis, there may be tiny pathogens in the genital area, but no obvious exudative lesions have yet to be caused. At this time, unprotected sexual intercourse with others is entirely possible to transmit syphilis to others. Latent syphilis, especially early latent syphilis, is highly contagious.

In primary syphilis, a chancre appears. If observed with a dark field microscope, a large number of Treponema pallidum can be found inside. Direct contact of mucous membranes or incomplete skin with the lesions can cause transmission, so protection must be taken when contacting primary syphilis lesions. When the chancre has exudative lesions, the risk of infection is relatively high when having unprotected sex with others.

During the course of syphilis infection, the earlier the infection, the more contagious it is, but the later it is, the less contagious it is. If you are infected with syphilis without knowing it, and the entire development process lasts for more than 4 years, the contagiousness will be significantly reduced.

3. How long does it take to detect syphilis infection?

Generally, 10 days after high-risk behavior, you can go to the hospital to draw blood for the corresponding syphilis serological test, which should give some indication. Of course, the longer the interval, the more reliable the serological prompt effect, because it takes time for the pathogen to enter the body and the immune response, such as the time for IgG to be produced, which is generally considered to be 10-14 days.

Therefore, serological tests are usually performed to assist in the diagnosis of syphilis, usually about 2 weeks after exposure. This ulcerative lesion will appear at the site of infection about 3-6 weeks later.

If syphilis is detected, Treponema pallidum is very sensitive to penicillin. As long as you are not allergic to penicillin, penicillin is the first choice for treatment. Primary syphilis is often treated with long-acting penicillin, 1.2 million units of which are injected into both buttocks once a week. In most cases, continuous injections are required for 3 weeks. The effective clearance rate of Treponema pallidum can reach 95%-100%, and the treatment effect is still very ideal.