Cysticercus fasciolaris infection in wild rats (Rattus norvegicus) in Korea and formation of cysts by remodeling of collagen fibers.

Cysticercus fasciolaris, the larval form of Taenia taeniaeformis, is commonly encountered in rodents. In our study, 287 wild rats (Rattus norvegicus) in South Korea were examined in 2010 and 2011. Of 287 rats, 97 (33.8%) were infected with C. fasciolaris A strong positive correlation was found between the host body weight and prevalence in both sexes, regardless of the year of collection. The liver was the most common habitat of the parasite, and the lung was the most frequent ectopic region, followed by mesentery, pleura, abdominal wall, and kidney. The lesions of the affected organs were generally characterized by well-developed cysts, each containing a larva. However, the cysts within kidney and abdominal wall were poorly organized, filled with abscess, and lacked larvae. Collagen types I and III, but not type IV, played significant roles in constructing the cysts at differential stages, addressed by immunohistochemistry. During cyst wall development, both collagen types contributed equally to cyst formation at the early stage, whereas collagen type I was the major component at the late stage (p < 0.05). In early-stage cysts, distribution of collagens was interestingly differential depending on the development stage, as collagen type I was localized in the outer layer and type III was located in the inner layer. Our results suggest that an appropriate remodeling process of collagen fibers is necessary for C. fasciolaris to build the well-conditioned cysts in the target organs for survival.