Potential role of beavers (Castor fiber) in contamination of water in the Masurian Lake District (north-eastern Poland) with protozoan parasites Cryptosporidium spp. and Giardia duodenalis

The purpose of this study was to assess the possible influence of beavers on the contamination of lake water with zoonotic parasites Giardia duodenalis and Cryptosporidium spp., with respect to the risk to human health. A total of 79 water samples were taken around the habitats of beavers from 14 localities situated in the recreational Masurian Lake District (north-eastern Poland). Water was sampled in the spring and autumn seasons, at different distances from beavers’ lodges (0-2, 10, 30, and 50 m). The samples were examined for the presence of (oo)cysts of zoonotic protozoa Giardia duodenalis and Cryptosporidium spp. by direct fluorescence assay (DFA) and by nested and real time PCR. By DFA, the presence of Giardia cysts was found in 36 samples (45.6%) and the presence of Cryptosporidium oocysts in 26 samples (32.9%). Numbers of Giardia cysts, Cryptosporidium oocysts, and summarised (oo)cysts of both parasites showed a significant variation depending on locality. The numbers of Giardia cysts significantly decreased with the distance from beavers’ lodges while the numbers of Cryptosporidium oocysts did not show such dependence. The amount of Giardia cysts in samples collected in spring was approximately 3 times higher than in autumn. Conversely, a larger number of Cryptosporidium oocysts were detected in samples collected in autumn than in spring. By PCR, Giardia DNA was found in 38 samples (48.1%) whereas DNA of Cryptosporidium was found in only 7 samples (8.9%). Eleven Giardia isolates were subjected to phylogenetic analysis by restriction fragment length polymorphism PCR or sequencing which evidenced their belonging to zoonotic assemblages: A (3 isolates) and B (8 isolates). In conclusion, water in the vicinity of beavers’ lodges in the tested region was markedly contaminated with (oo)cysts of Giardia duodenalis and Cryptosporidium spp., which confirms the potential role of beavers as a reservoir of these parasites and indicates a need for implementation of appropriate preventive measures to protect tourists’ health.