Background:
Leptospirosis, caused by Leptospira spirochetes, is considered the most widespread zoonosis worldwide. Morbidity may be increased by natural disasters such as floods or typhoons.

Aim of the study:
The aim of the present study was to investigate the epidemiological situation of leptospirosis in the Lublin Region (Eastern Poland) with consideration of the effects of flooding by the Vistula River, by investigating human population and various elements of the environment for the presence of Leptospira in two areas: ‘Area A’ exposed to flooding, and ‘Area B’ not exposed to flooding.

Material and Methods:
In the Areas A and B, sera of 100 and 98 inhabitants, sera of 32 and 41 pigs and sera of 41 and 40 cows were examined, respectively, for the presence of anti-Leptospira antibodies by the microscopic agglutination test (MAT), as well as 40 and 64 samples of water, 40 and 68 samples of soil, organ samples of 30 and 30 small mammals from 5 and 6 species, and 540 and 296 Ixodes ricinus ticks, respectively – for the presence of Leptospira DNA by the nested-PCR test.

Results:
The presence of anti-Leptospira antibodies was found in 3% of inhabitants of Area A and in 9.2% of Area B; this difference was statistically insignificant. The frequency of anti-Leptospira antibodies was higher in pigs and cows from Area A, compared to area B (34.4% vs. 4.9%, and 26.8% vs. 15.0%, respectively), while in the case of pigs the difference was significant (P=0.0015). Also, the titers of positive reactions were higher in Area A, compared to Area B, and for cows the difference was significant (P=0.0128). The presence of Leptospira DNA was found in 20% of small mammals from Area A, and in 30% from Area B; this difference being insignificant; however, in both cases the frequency of positive results was high, compared to the data from literature. The great majority of positive results were obtained in striped field mice (Apodemus agrarius). The presence of Leptospira DNA was detected in 15.6% of I. ricinus ticks from Area A, compared to 1.4% in Area B, and the difference was highly significant (P<0.0001). 5% of water samples from Area A contained Leptospira DNA, whereas all water samples from Area B, and all soil samples from Areas A and B were negative.

Conclusions:
The infections with Leptospira spirochetes among the rural population inhabiting the areas of the Lublin Region exposed to floods by the Vistula River do not occur with a higher frequency, compared to the areas not exposed to floods. • The potential sources of infection with Leptospira in the areas exposed to flooding are animals: ticks Ixodes ricinus, domestic animals (pigs, cows), and striped field mice (Apodemus agrarius). • Detection of Leptospira spp. DNA in 5% of water samples in the areas exposed to floods, with negative results in control areas, seems to confirm a possible role of water in spreading leptospirosis. • Soil does not constitute any significant risk of infection in the areas exposed to flooding.