Diagnosing the increasing incidence of syphilis

The causative organism of syphilis - the incidence of which continues to grow - is Treponema pallidum, a spirochaete which cannot be grown on culture media or in tissue culture

Oxoid diagnostic reagent VDRL and TPHA kits can provide laboratories with inexpensive, easy-to-perform and rapid tools for the diagnosis of syphilis - the incidence of which continues to rise in the UK.

Following a House of Commons health committee report in June 2003 that showed that the UK's sexual health services were in crisis, in September the government announced an extra £11m of funding for sexual health services.

However, no funding was specifically allocated for microbiology and laboratory services or for diagnosis of the 'traditional' STIs such as syphilis, and yet rates of infection with this disease continue to rise.

Figures from the Health Protection Agency show that between 2001 and 2002 syphilis diagnoses went up by 67% and 33% in males and females respectively and, according to the health committee report, in the last six years syphilis rates have increased by 500%.

The causative organism of syphilis is Treponema pallidum, a spirochaete which cannot be grown on culture media or in tissue culture.

The infection is normally diagnosed by the detection of antibody specific for Treponema pallidum in the patient's blood or CSF.

Detection of the antibody becomes possible after 3-4 weeks following infection.

Two groups of antibodies are formed in response to infection.

The first group - reagin antibodies - are antibodies reactive with non-treponemal antigens and are normally found in the active disease.

These can be detected by using the Oxoid VDRL carbon antigen test (DR525M).

This rapid agglutination test is simple to perform.

50ml of test sample is spread over a test circle on the cards provided and one drop of antigen is added.

The card is then rotated for eight minutes.

Large aggregates in the centre or periphery of the test circle indicate strongly or moderately reactive sera.

The second group are antibodies reactive with the specific antigens of T pallidum.

These specific antibodies persist long after the infection has been successfully treated.

The Oxoid TPHA test is a sensitive passive haemagglutination test specifically for the detection of antibodies to Treponema pallidum.

When diluted positive samples are mixed with the test cell suspension in a microtitre plate, antibody to the sensitising antigen causes agglutination of the cells.

The cells form a characteristic pattern in the bottom of the plate well - agglutinated cells form an even layer over the bottom of the well; non-agglutinated cells form a compact button at the centre of the well; weakly agglutinated cells form a characteristic ring pattern.

Agglutination of the test cells but not the control cells indicates the presence of specific antibody to T pallidum.

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