Human Mozdok leptospirosis first diagnosed by serum agglutinin-absorption tests in the Slovak Republic

The serovar Mozdok related leptospirosis in humans were not yet feasibly diagnosed using merely the standard micro-agglutination test (MAT) what was perhaps due to the impossibility to distinguish them from illnesses that are caused by Leptospira strains belonging to other serovars of the serogroup Pomona. On the contrary, leptospires of the Mozdok serovar were cultured from rodents and domestic animals world-wide including Central Europe where only Leptospira strains of the serovars Pomona and Mozdok are known to be present till now.

The aim of the study was to discover if leptospires of Mozdok serovar may cause human leptospirosis that remained hidden till now among infections diagnosed merely by MAT as Pomona illnesses.

The reference Leptospira strains of Pomona and Mozdok serovars (Pomona and 5621), as well as three endemic, and in some tests only two strains of human and pig origin (Šimon, S-23, Pöštényi), and two strains of rodent provenance - Apodemus agrarius (M-210/98 and M-71/01) were used for this purpose. First, the endemic strains were assigned to one of the afore-mentioned two serovars by agglutinin cross-absorption tests performed using rabbit immune sera, monoclonal antibodies and random amplified polymorphic DNA methods. Afterwards, twenty-one sera of patients with a Pomona leptospirosis confirmed by MAT were examined by agglutinin absorption test (AAT).

Based on the results of the mentioned laboratory method used, the endemic Leptospira strains of human and pig origin could be affiliated to the serovar Pomona, while those of rodent origin were classified as serovar Mozdok strains. Out of the 21 patients sera, an illness caused by the serovar Mozdok strains was found out in 13 cases and a disease caused by serovar Pomona strains in 8 cases. Their differentiation was made on the strength of the following results of AATs: All strains from the serovar Mozdok have completely absorbed antibodies (anti-Pomona and anti-Mozdok) from the tested sera, however following the absorption of these sera with the Pomona strains, high levels of residual antibodies reacting in MAT with the Mozdok strains have still persisted. In this way, it was possible to prove the Mozdok infection in thirteen patients. On the contrary, following the absorption of the sera with the strains of the serovar Pomona, a complete absorption of all antibodies (anti-Pomona and anti-Mozdok) was achieved in seven cases using the strain Šimon, and in one case with the strain S-23, whereas after absorption using the Pomona strain, the residual antibodies were still present in all sera, and also in the majority of them when they were absorbed using the strains S-23 and Pöštényi. In this context, the Pomona infection was determined in the case of eight patients. Hence it follows that not all strains of the Pomona serovar were suitable for the AATs.

The presence of the human Mozdok leptospirosis was confirmed for the first time by the use of the agglutinin absorption test. A clear correlation between the habitat areas of the A. agrarius and the patients who were infected with the strains of the Mozdok serovar was determined.