Serodiagnosis of bacterial diseases: problems and developments

Serodiagnosis is useful when pathogens cannot be detected quickly or easily by conventional methods or have been eliminated by the patient. Taking the example of leptospirosis, the microscopic agglutination test to detect specific antibodies after leptospires have disappeared from the patient's bloodstream is of unsurpassed reliability. Unfortunately the test is used mainly in specialized laboratories that can culture leptospires to serve as live antigens. Freeze-dried leptospires may allow the application of the test on a wide scale. The ELISA is useful for the detection of IgM antibodies in humans as a sign of current or recent infection. ELISA results must be confirmed by the microscopic agglutination test. A simplified easy-to-read ELISA using broadly reactive antigen for the detection of all types of leptospires might be useful for a quick detection of acute human leptospirosis. Using an appropriate antigenic preparation the ELISA is useful for the detection of antibodies in animals, e.g. cattle. As for pathogen detection, DNA-based methods such as PCR are promising for an early, quick and specific diagnosis. Antigenic analysis by monoclonal antibodies and genetic analysis by restriction fragment length polymorphism are for the time being complementary methods for the characterization of leptospiral isolates.