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Leptospirosis: antibodies to the causative agent of leptospirosis in the blood
Last reviewed: 23.04.2024
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Antibodies to the causative agent of leptospirosis in serum are normally absent.
Leptospirosis is a natural focal infectious disease characterized by the defeat of capillaries, kidneys, liver, muscles, cardiovascular and nervous systems, accompanied or not accompanied by jaundice. All pathogenic leptospira are combined into one species - Leptospira interrogans, it includes various serological variants (more than 200 serovars are known). To diagnose leptospirosis, use microscopic (blood or CSF in a dark field or colored preparations according to Romanovsky-Giemsa), bacteriological (blood cultures are positive in almost 90% of cases in the first 3 days of the disease, after the first week of the disease, spirochetes can be found in urine) and serological (RSK, ELISA) methods.
When using RSK, antibodies to leptospirae (IgM and IgG) are detected in the blood on the 10th-21st day after clinical manifestations of the disease. The increase in titer by more than 4 times in the study of paired sera indicates infection. Elevated antibody titers can persist for years. As a diagnostic titer for a single study of DAC recommend values of 1: 1600 and above. Positive results of DSC should be confirmed by the indirect agglutination reaction, ELISA, or better Western-blot because of a possible cross-reaction with antibodies to the virus hepatitis A virus, the causative agent of syphilis, cytomegalovirus and mycoplasma.
RPHA is used to confirm DSC - screening method. The sensitivity of the RPHA is 92%, the specificity is 95%.
ELISA allows detecting antibodies of classes IgM and IgG to leptospira. Antibodies of IgM class can be found in the blood on the 4th-5th day of the disease, their titer reaches a peak at the 2-3rd week, then decreases within months. IgG antibodies appear on the 3-4th week of the disease, their titer reaches a peak between the 4th and the 6th month after the onset of the disease and persists for years. The presence of IgM antibodies in the serum or a 4-fold increase in the IgG antibody titer allows diagnosis of the disease. To confirm the positive results of the IgM and IgG antibody detection to leptospira, Western-blot is recommended (the presence of IgM antibodies is confirmed if antibodies to 2 or 3 proteins are detected - 24, 39, 41 and kD 2, AT IgG - in the presence of antibodies to 5 proteins from the following - 18, 21, 28, 30, 39, 41, 45, 58, 66 and 93 kD 2 ).
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