[The impact of nematode invasions on the pattern of Cryptosporidium parvum infection in wild rodents].

Fragmentation of the environment by natural barriers (lakes, mountain ranges) and human activities (towns, major roads, agriculture) can lead to isolated subpopulations of hosts. The study was carried out in Mazury Lake District in North-East of Poland, the region rich in forests, lakes, rivers and canals, which are able to create passable such barriers. Population of bank voles (Myodes glareolus) and yellow-necked mice (Apodemus flavicollis)--dominant woodland rodents--showed local differences in helminth communities in fragmented forest habitat. The sites were chosen on the basis of the similarity of their habitat structure and type, and isolation from one another. The impact of nematode (Heligmosomoididae) infections on co-occurrence and dynamic of Cryptosporidium parvum infection was studied in both rodent species Myodes glareolus (n=781) and Apodemusflavicollis (n=302) from three different habitats. Presented results clearly revealed that natural nematode invasion could facilitate the presence of chronic infections of Cryptosporidium parvum in wild rodent populations. Also, the intrinsic (host sex and year) as well as extrinsic (season and year of study) factors have obvious effect on dynamics of infections with both groups of parasites. However, there are also some evidences that steroids hormones associated with stress and reproduction may mediate trade-offs between physiology and immune function and can affect co-occurrence of both groups of parasites.