Syphilis is a sexually transmitted disease (STD) caused by a bacterium called Treponema pallidum. The initial infection causes an ulcer at the site of infection; however, the bacteria move throughout the body, damaging many organs over time. Medical experts describe the course of the disease by dividing it into four stages – primary, secondary, latent, and tertiary (late). An infected person who has not been treated may infect others during the first two stages, which usually last one to two years. In its late stages, untreated syphilis, although not contagious, can cause serious heart abnormalities, mental disorders, blindness, and other neurological  problems, and death.

The bacterium spreads from the initial ulcer of an infected person to the skin or mucous membranes of the genital area, the mouth, or the anus of a sexual partner. It also can pass through broken skin on other parts of the body. The syphilis bacterium is very fragile, and the infection is almost always spread by sexual contact. In addition, a pregnant woman with syphilis can pass the bacterium to her unborn child, who may be born with serious mental and physical problems as a result of this infection. But the most common way to get syphilis is to have sex with someone who has an active infection.

Symptoms
The first symptom of primary syphilis is an ulcer called a chancre ("shan-ker"). The chancre can appear within 10 days to three months after exposure, but it generally appears within two to six weeks. Because the chancre may be painless and may occur inside the body, it may go unnoticed. It usually is found on the part of the body exposed to the partner’s ulcer, such as the penis, the vulva, or the vagina. A chancre also can develop on the cervix, tongue, lips, or other parts of the body. The chancre disappears within a few weeks whether or not a person is treated. If not treated during the primary stage, about one-third of people will progress to chronic stages.

Secondary syphilis is often marked by a skin rash that is characterized by brown sores about the size of a penny. The rash appears anywhere from three to six weeks after the chancre appears. While the rash may cover the whole body or appear only in a few areas, the palms of the hands and soles of the feet are almost always involved. Because active bacteria are present in these sores, any physical contact – sexual or nonsexual – with the broken skin of an infected person may spread the infection at this stage. The rash usually heals within several weeks or months. Other symptoms also may occur, such as mild fever, fatigue, headache, sore throat, as well as patchy hair loss, and swollen lymph glands throughout the body. These symptoms may be very mild and, like the chancre of primary syphilis, will disappear without treatment. The signs of secondary syphilis may come and go over the next one to two years.

If untreated, syphilis may lapse into a latent stage during which the disease is no longer contagious and no symptoms are present. Many people who are not treated will suffer no further consequences of the disease. Approximately one-third of those who have secondary syphilis, however, go on to develop the complications of late, or tertiary, syphilis, in which the bacteria damage the heart, eyes, brain, nervous system, bones, joints, or almost any other part of the body. This stage can last for years, or even for decades. Late syphilis, the final stage, can result in mental illness, blindness, and other neurological problems, heart disease, and death.

Neurosyphilis
Syphilis bacteria frequently invade the nervous system during the early stages of infection, and approximately 3 to 7 percent of persons with untreated syphilis develop neurosyphilis. Some persons with neurosyphilis never develop any symptoms. Others may have headache, stiff neck, and fever that result from an inflammation of the lining of the brain. Some patients develop seizures. Patients whose blood vessels are affected may develop symptoms of stroke with resulting numbness, weakness, or visual complaints. In some instances, the time from infection to developing neurosyphilis may be up to 20 years. Neurosyphilis may be more difficult to treat and its course may be different in people with HIV infection.

Diagnosis
Syphilis has sometimes been called "the great imitator" because its early symptoms are similar to those of many other diseases. Sexually active people should consult a doctor about any suspicious rash or sore in the genital area. Those who have been treated for another STD, such as gonorrheae, should be tested to be sure they have not also acquired syphilis.

There are three ways to diagnose syphilis: a doctor's recognition of its signs and symptoms; microscopic identification of syphilis bacteria; and blood tests. The doctor usually uses these approaches together to detect syphilis and decide upon the stage of infection.

To diagnose syphilis by identifying the bacteria, the doctor takes a scraping from the surface of the ulcer or chancre, and examines it under a special "darkfield" microscope to detect the organism itself. Blood tests also provide evidence of infection, although they may give false- negative results (not show signs of infection despite its presence) for up to three months after infection. False-positive tests also can occur; therefore, two blood tests are usually used. Interpretation of blood tests for syphilis can be difficult, and repeated tests are sometimes necessary to confirm the diagnosis.

The blood-screening tests most often used to detect evidence of syphilis are the VDRL (Venereal Disease Research Laboratory) test and the RPR (rapid plasma reagin) test. The false-positive results (showing signs of infection when it is not present) occur in people with autoimmune disorders, certain viral infections, and other conditions.

Therefore, a doctor will administer a confirmatory blood test when the initial test is positive. These tests include the fluorescent treponemal antibody-absorption (FTA-ABS) test that can accurately detect 70 to 90 percent of cases. Another specific test is the T. pallidum hemagglutination assay (TPHA). These tests detect syphilis antibodies (proteins made by a person's immune system to fight infection). They are not useful for diagnosing a new case of syphilis in patients who have had the disease previously because once antibodies are formed, they remain in the body for many years. These antibodies, however, do not protect against a new syphilis infection. In some patients with syphilis (especially in the latent or late stages), a lumbar puncture (spinal tap) must be done to check for infection of the nervous system.

Treatment
Syphilis usually is treated with penicillin, administered by injection. Other antibiotics can be used for patients allergic to penicillin. A person usually can no longer transmit syphilis 24 hours after beginning therapy. Some people, however, do not respond to the usual doses of penicillin. Therefore, it is important that people being treated for syphilis have periodic blood tests to check that the infectious agent has been completely destroyed. Persons with neurosyphilis may need to be retested for up to two years after treatment. In all stages of syphilis, proper treatment will cure the disease, but in late syphilis, damage already done to body organs cannot be reversed.

Effects of Syphilis in Pregnant Women
It is likely that an untreated pregnant woman with active syphilis will pass the infection to her unborn child. About 25 percent of these pregnancies result in stillbirth or neonatal death. Between 40 to 70 percent of such pregnancies will yield a syphilis-infected infant.

Some infants with congenital syphilis may have symptoms at birth, but most develop symptoms between two weeks and three months later. These symptoms may include skin sores, rashes, fever, weakened or hoarse crying sounds, swollen liver and spleen, yellowish skin (jaundice), anaemia, and various deformities. Care must be taken in handling an infant with congenital syphilis because the moist sores are infectious.

Rarely, the symptoms of syphilis go undetected in infants. As infected infants become older children and teenagers, they may develop the symptoms of late-stage syphilis including damage to their bones, teeth, eyes, ears, and brain.