Syphilis is caused by the Spirochete bacterium called Treponema pallidum (TP). It is primarily sexually transmitted or from mother to child during pregnancy. The bacterium can also be transmitted by blood transfusion. Screening for Syphilis in risk populations is important for restriction and prevention of the spread of the disease.
Syphilis progresses through four stages – primary, secondary, latent, and tertiary. If untreated or not treated early enough it can become life-threatening as organisms moving through the body can cause damage to internal organs.
Each year there are an estimated 5.6 million new Syphilis infections worldwide, according to estimates by the World Health Organization.
There are two categories of serological tests for Treponema pallidum in diagnosing Syphilis. The first serological test, the non-treponemal test, targets the lipid antigen (VDRL and RPR), while the second is a treponemal-specific test (such as TPHA and FTA-ABS). Due to poor specificity and sensitivity and the likelihood of false positive and false negative results, alternative tests using enzyme-linked assays have been developed to replace the present TP serological diagnostic and screening test. These enzyme-linked assays that utilize recombinant proteins for detection of TP antibodies are routinely used in clinical laboratory practice and blood donor screening.
Following infection, antibodies to a wide range of antigens, including non-specific antibodies and specific anti-TP antibodies, are being produced. Specific antitreponemal IgM start appearing in the first two weeks of infection. Antitreponemal IgG appears about four weeks later. In the most cases both IgG and IgM can be detected by the time symptoms develop.