Syphilis is a sexually transmitted infection (STD), once responsible for devastating epidemics. It is caused by a bacterium called Treponema pallidum. The rate of primary and secondary syphilis in the United States declined by 89.2 percent from 1990 to 2000. The number of cases rose, however, from 5,979 in 2000 to 6,103 in 2001. The U.S. Centers for Disease Control and Prevention reported in November 2002 that this was the first increase since 1990.

Of increasing concern is the fact that syphilis increases by 3- to 5-fold the risk of transmitting and acquiring HIV (human immunodeficiency virus), the virus that causes AIDS (acquired immunodeficiency syndrome).

The syphilis bacterium is very fragile, and the infection is almost always transmitted by sexual contact with an infected person. The bacterium spreads from the initial ulcer (sore) of an infected person to the skin or mucous membranes (linings) of the genital area, mouth, or anus of an uninfected sexual partner. It also can pass through broken skin on other parts of the body.

In addition, a pregnant woman with syphilis can pass T. pallidum to her unborn child, who may be born with serious mental and physical problems as a result of this infection.

The initial infection causes an ulcer at the site of infection. The bacteria, however, 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 1 to 2 years. In its late stages, untreated syphilis, although not contagious, can cause serious heart abnormalities, mental disorders, blindness, other neurologic problems, and death.

The first symptom of primary syphilis is an ulcer called a chancre ("shan-ker"). The chancre can appear within 10 days to 3 months after exposure, but it generally appears within 2 to 6 weeks. Because the chancre may be painless and may occur inside the body, the infected person might not notice it. It usually is found on the part of the body exposed to the infected partner's ulcer, such as the penis, vulva, or 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 go on to the chronic stages.

A skin rash, with brown sores about the size of a penny, often marks this chronic stage of syphilis. The rash appears anywhere from 3 to 6 weeks after the chancre appears. While the rash may cover the whole body or appear only in a few areas, it is almost always on the palms of the hands and soles of the feet.

Because active bacteria are present in the 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, 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 1 to 2 years of the disease.

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 from no further signs and symptoms of the disease.

Approximately one-third of people who have had secondary syphilis 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 can result in mental illness, blindness, other neurologic problems, heart disease, and death.

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

There are three ways to diagnose syphilis.

Recognizing the signs and symptoms
Examining blood samples
Identifying syphilis bacteria under a microscope

The doctor usually uses all these approaches to diagnose syphilis and decide upon the stage of infection.

Blood tests also provide evidence of infection, although they may give false-negative results (not show signs of an infection despite its presence) for up to 3 months after infection. False-positive tests (showing signs of an infection when it is not present) 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.

Unfortunately, the early symptoms of syphilis can be very mild, and many people do not seek treatment when they first become infected.

Doctors usually treat patients with syphilis with penicillin, given by injection. They use other antibiotics for patients allergic to penicillin. A person usually can no longer transmit syphilis 24 hours after starting treatment. 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.

People with neurosyphilis may need to be retested for up to 2 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.

Syphilis bacteria frequently invade the nervous system during the early stages of infection. Approximately 3 to 7 percent of persons with untreated syphilis develop neurosyphilis, a sometimes serious disorder of the nervous system. In some instances, the time from infection to developing neurosyphilis may be up to 20 years.

Some people 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 people develop seizures. People whose blood vessels are affected may develop symptoms of stroke with numbness, weakness, or visual problems. Neurosyphilis may be more difficult to treat, and its course may be different, in people with HIV infection or AIDS.