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Leptospirosis: antibodies to leptospirosis pathogen in blood
Last reviewed: 05.07.2025
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Antibodies to the causative agent of leptospirosis are normally absent in the serum.
Leptospirosis is a natural focal infectious disease characterized by damage to the capillaries, kidneys, liver, muscles, cardiovascular and nervous systems, accompanied or not by jaundice. All pathogenic leptospires are combined into one species - Leptospira interrogans, which includes various serological variants (more than 200 serovars are known). To diagnose leptospirosis, microscopic (blood or cerebrospinal fluid examination in a dark field or stained preparations according to Romanovsky-Giemsa), bacteriological (blood cultures are positive in almost 90% of cases in the first 3 days of illness; after the first week of illness, spirochetes can be detected in urine) and serological (RSK, ELISA) methods are used.
When using the CSC, antibodies to leptospira (IgM and IgG) are detected in the blood on the 10th-21st day after the clinical manifestations of the disease. An increase in the titer by more than 4 times in the study of paired sera indicates infection. An increased antibody titer can persist for years. As a diagnostic titer for a single CSC study, values of 1:1600 and higher are recommended. A positive CSC result must be confirmed by an indirect agglutination reaction, ELISA, or better yet, Western blot due to a possible cross-reaction with antibodies to the hepatitis A virus, the causative agent of syphilis, cytomegalovirus, and mycoplasma.
RPGA is used to confirm the CSC - screening method. The sensitivity of RPGA is 92%, specificity - 95%.
ELISA allows to detect IgM and IgG antibodies to leptospira. IgM antibodies can be detected in the blood on the 4th-5th day of the disease, their titer reaches a peak on the 2nd-3rd week, then decreases over the course of months. IgG antibodies appear on the 3rd-4th week of the disease, their titer reaches a peak between the 4th and 6th month after the onset of the disease and persists for years. The presence of IgM antibodies in the blood serum or a 4-fold increase in the IgG antibody titer allows to diagnose the disease. To confirm positive results of determining IgM and IgG class antibodies to leptospira, it is recommended to use the Western-blot method (the presence of IgM antibodies is confirmed if antibodies to 2 or 3 proteins are detected - 24, 39, 41 and kD 2; IgG AT - 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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