Syphilis is a disease caused by a spiral-shaped bacterium called a spirochete. Spirochetes are members of the family Spirochaetaceae which include long, slender, coiled, motile microorganisms. Three genera of spirochetes contain species that are able to cause disease in humans: Treponema (syphilis), Borrelia (relapsing fever), and Leptospira (leptospirosis). The last two diseases are caused by spirochetes that infect ticks or lice and transmitted to humans through their bites.
The treponemas are highly motile and move through fluid with a twisting motion. They cannot be grown on any artificially cultured medium. Humans are the only natural host, but monkeys and rabbits can be infected for experimental purposes. The organism is readily killed by disinfectants, and are highly susceptible to penicillin and other antibiotics.
Syphilis (T. pallidum) is an age-old sexually transmitted disease which can also be transmitted through heavy kissing, passing through an infected area on the lips. It can also be acquired through transfusions since the bacteria eventually passes into the bloodstream. However, these occurrences are very rare. The bacterium can easily be killed within minutes if soap and water are used. It cannot penetrate unbroken skin and it does not like dry places. There is no vaccine, but penicillin remains effective and, to date, it has not developed resistance. Because it adapts so well to living tissue, it cannot be artificially cultured. Syphilis is somewhat unusual in that both specific and nonspecific antibodies are formed against the infecting organism, but neither is protective against reinfection. In fact, many of the clinical symptoms are the result of the person’s own immune response to the organism.
Syphilis is very similar to leprosy and remained indistinct until the 15th century. By the 17th century, syphilis infection was running simultaneously with gonorrhea. For years, syphilis was treated with mercury, causing side effects almost as deadly as the disease itself. T. pallidum was not identified as the cause until 1905. Various drugs proved to be effective, including Salvarsan, an arsenic compound, which produced irreversible side effects, however. Eventually, the German scientist Paul Ehrlich perservered until he developed a safer drug called Neosalvarsan, which was used during WWI. In the 1930s, the US Public Health Service conducted a very controversial experiment called the Tuskegee experiment, where several hundred African American men in Georgia who had contracted the disease, were allowed to advance to various stages solely for experimental purposes. It had very little scientific value since the symptoms were well documented, and penicillin could well have stopped the advancement of the disease, but was intentionally withheld. By the late 1980s, the disease has proven to be on the rise again.
Among the sexually transmitted diseases, syphilis is second to gonorrhea, the most frequently reported sexually transmitted disease. However, syphilis is far more serious than gonorrhea, and, if left untreated, will go through several stages over an extended period of time. The stages of syphilis are primary, secondary, tertiary or latent, and late stage. Congenital syphilis also occurs when the disease is transferred in utero from an infected woman to her fetus.
- Stage 1: Primary syphilis
- Sexual contact is almost always the mode of transmission. Treponema are able to penetrate the mucosal tissues or gain entry through small lesions in the skin. The bacteria begin to multiply at the site, and then are carried to nearby lymph nodes and eventually into the bloodstream. Ten to thirty days later, but occasionally as much as seventy, a primary lesion appears at the site of infection, usually on the genital tissues. This lesion is called a chancre – a shallow, relatively painless ulcer. It can grow to more than a centimeter in diameter and is teeming with spirochetes. This chancre can go unnoticed in women especially because if its location is in the deeper passages of the genital tract. This primary stage of the disease lasts until the chancre goes away, usually between three and six weeks, convincing many that they are cured. The person may then appear to be asymptomatic for two weeks to six months before the second stage begins.
- Stage 2: Secondary syphilis
- The spirochetes that spread through the body during the primary stage become deposited in many tissues where they slowly multiply. Secondary syphilis is characterized by the appearance of a generalized body rash and lesions anywhere on the body including the bones, central nervous system, or other internal organs. These lesions on the skin and mucus membranes may contain large numbers of spirochetes and are highly infectious. Other accompanying symptoms may include headaches, fever, and sore throat. Lesions on the skin are quite prominent and are often referred to as the “great pox.” As the secondary stage begins to subside, complete recovery will be slow, often taking several years.
- Stage 3: Tertiary or latent syphilis
- This period usually displays no apparent symptoms, but high levels of antibodies remain in the serum. About half of the patients will have no further symptoms of the disease, but the other half will progress to the last stage.
- Stage 4: Late-stage syphilis
- Symptoms involved in this stage of the disease may not appear for three to thirty years following the second stage. However, in those infected with HIV, symptoms can develop rapidly and appear within only a few months following the secondary stage. In this stage, lesions called gummas develop in various areas of the body, including the central nervous system. This usually results in a disorder referred to as neurosyphilis, a major cause of insanity. Mental changes may often resemble other neurologic diseases. In addition, the cardiovascular system is often involved with a frequent development of aneurysms in the aorta. In the years prior to 1986, the number of late-stage syphilis cases declined, but the trend suddenly reversed itself, doubling in the following two years.
Congenital syphilis occurs when an infected pregnant woman passes the T. pallidum organism to her developing fetus. By the mid-1980s, a remarkable and steady increase in congenital syphilis was seen. The fetus will not develop any symptoms of the disease until the second trimester when the spirochetes become disseminated throughout its body. Almost half will die as a result of stillbirth or spontaneous abortion. Over half of the infected infants born will show marked congenital defects. Others will appear normal at birth, but later develop symptoms that may include the following: skin lesions, enlarged spleens, anemia, pneumonia, eye damage, neurologic lesions, mental retardation, and deformities of the bones, teeth, or cartilage tissue.
The FTA (abs) test is the first serological test used for syphilis to become positive following an infection. The problem with it is that there is a chance of obtaining a false-positive reaction. Therefore, any positive reaction should be followed up with at least one other test. Patients with autoimmune diseases, particularly SLE (systemic lupus erythematosus), are prone to false positive TPHA and FTA (abs) tests, as are IV drug abusers, and occasionally those with malaria or leprosy who become pregnant.
For those allergic to penicillin, erythromycin or tetracyclines are the drugs of choice. Some who are given antibiotics can suffer a toxic reaction known as the Jarisch-Herxheimer reaction. It is caused as the dying bacteria release toxins that produce fever, rapid pulse, and respirations, and a drop in blood pressure. These reactions are often symptoms of toxic shock or septicemia.
Such other syphilis-like diseases as yaws (T. pertenue), pinta, and bejel are caused by bacteria either closely related to or identical with the syphilis spirochete. These diseases are not necessarily transmitted through sexual contact, but often by direct contact. They usually occur in people living in very poor conditions, especially in the Mideast where such diseases were almost irradicated, but have since seen a resurgence. Millions of people, mostly children, contract these contagious diseases each year. Another related microorganism is T. microdentium, which inhabits the mouth of humans as normal flora.