How Can You Test for Syphilis?

Syphilis is caused by a bacterium called Treponema pallidum. Syphilis is a highly contagious infection that is easily spread via vaginal, anal and oral sex. Congenital syphilis occurs when the disease is transmitted from an infected mother to her child during childbirth, resulting in abnormalities, complications, or even death. The disease is treatable in the early stages but can result in serious and irreversible damage if the infection is not treated. This disease is often called ‘The Great Imitator’ because the symptoms are very similar to those displayed by many other diseases, which can result in confusion, misdiagnosis, and mistreatment - leading to further complications.

It is important to know the diagnostic methods for detecting syphilis bacteria. No commercial test is available to test syphilis, but there are some classic ways of detecting syphilis. The important part here is to get the diagnosis done in the right amount of time, that is, in the primary or secondary stages of the infection, as they are easy to detect and to treat as well.

Testing for the presence of syphilis follows a two step methodology of identifying and then confirming the presence of the infection. This process requires a sample of tissue, blood or liquid from a syphilis sore. The presence of antibodies is confirmed with blood tests, while the T pallidum bacteria can be confirmed with fluid and tissue tests. Tests that use tissue and fluid from the sore can only be done when there is presence of rashes or sores, and that restricts the efficacy of testing in the later stages of the infection. Sometimes antibodies are present in the blood post treatment, resulting in a positive test even after being cured.

There are three important approaches:

• Microscopy: The bacteria are present in the chancre or in the condyloma lata, therefore, the serous liquid from the chancre is taken and is tested using dark field microscopy or by direct fluorescent antibody (DFA) test. Gram staining cannot be done because they are not clearly visible. Histological tests can be performed on biopsy material from gumma which appear in tertiary syphilis. The histological stains which are used are silver stain or fluorescent antibody.
• Non-specific serological tests: This includes Venereal Disease Research Laboratory (VDRL) and rapid plasma regain (RPL) that detect presence of antibodies. Also non-treponemal antigens are used. The mammalian tissues react with antibodies which are a mixture of IgG and IgM (regain). Effectiveness of treatment can be seen by decrease in the titer of non-specific antibodies. Sometimes false reactions occur in some medical conditions like leprosy, hepatitis B, infectious mononucleosis and prozone phenomenon. In such phenomenon, the titer of antibody is too high and aggregation does not occur. But upon dilution positive results can be obtained. These tests are used for screening the population for syphilis. It is always advisable to get a confirmation test after non-specific tests due to the false results. Congenital syphilis can be detected using the VDRL test. This test is based on the finding of higher antibody titer in infant than mother. One-time testing may indicate that the presence of antibodies from mother since they cross placenta but if the titer remains high then a true infection can be suspected in the infant. Irrespective of tests of diagnostic tests, treatment should be done for infants whose mother have syphilis.
• Specific serological tests: Treponemal antigens are used in such tests, Immunofluorescence test and hemagglutination test. In immunofluorescence tests, fluorescent antibodies are used which aggregate with specific treponemal antigens. In haemagglutination tests, the antigens attach to the antibodies of the red blood cells. These antigens are obtained from the patient’s serum. Blood should be taken after 2-3 weeks of acquiring infection because the T. pallidum divides slowly.

Presumptive tests: To detect syphilis on the risk groups, it is better to do PCR because it can detect T. pallidum in very less amount. PCR or Polymerase Chain Reaction is a way to amplify the DNA and detect it. It proceeds via the following steps:

1. Initialization: The reaction has to be raised to a temperature till 94-98 degrees Celsius and is held for 1-9 minutes.
2. Denaturation step: In this step, the DNA helix unwinds by disrupting the hydrogen bonds and yields single stranded DNA strands. The temperature is high in this step till 96-96 degrees Celsius
3. Annealing step:  In this step, primer binds to single stranded DNA. This step requires lowering of temperature to 50-60 degrees Celsius which is important for the attachment between primer and DNA strand. It is important to maintain the temperature because any error in the temperature may result in an incorrect annealing step
4. Extension: Here, Taq polymerase is required to polymerize the DNA at 72 degrees Celsius. A new DNA strand is synthesized which is complementary to the old one

This cycle is repeated at least 20-40 times to get discreet DNA templates for detection.  

Testing blood can detect the infection as quickly as 1 to 2 weeks after exposure. Within 3 months the highest accuracy can be expected. Someone who has been exposed to a syphilis infection earlier could return a false positive because of antibodies present in the blood.

Treating and Curing Syphilis

Antibiotics can easily cure syphilis if treatment is started during the early stages. A single dose of penicillin can effectively treat and cure the infection. The physical and neurological damage seen in the cardiac and nervous systems during the third stage is irreversible. If the patient is allergic to penicillin, other antibiotics can be prescribed. Regular follow-up visits and testing is necessary for a year post treatment.

Why Treatment is so Important

Syphilis can easily spread to all areas of the body via the bloodstream. If left untreated, the disease can result in severe damage to the heart, brain, spinal cord, blindness and eventually death.

Syphilis testing is done to check for syphilis or to see how well the treatment is doing. Screening can assist the doctor in looking for any conditions even before symptoms appear. This makes it easier to find the infection s it can be treated quickly. Screening is often done in persons who engage in risky sexual behaviors.