The helminth fauna and metacommunity structure of eight sympatric sigmodontine rodents were investigated at the Serra dos Órgãos National Park, an Atlantic Forest reserve located in the State of Rio de Janeiro, southeast Brazil. Rodents of the species Abrawayaomys ruschii, Akodon montensis, Blarinomys breviceps , Delomys dorsalis, Oligoryzomys flavescens, Oligoryzomys nigripes, Oxymycterus quaestor and Thaptomys nigrita were found infected with helminths. Akodon montensis presented the highest total helminth species richness, with six different species of helminths. The nematode Stilestrongylus lanfrediae was the most abundant and prevalent helminth species observed. The host-parasite network analysis showed little interactions among host species. Akodon montensis seems to act as a keystone-species in the rodent community. This species shared the nematodes Stilestrongylus aculeata with A. ruschii and Protospirura numidica criceticola with T. nigrita, and the cestode Rodentolepis akodontis with D. dorsalis. The congeners host species O. flavescens and O. nigripes shared the nematodes Guerrerostrongylus zetta and S. lanfrediae. The rodents B. breviceps and O. quaestor did not share any helminths with other hosts. The helminth metacommunity showed a random pattern on both infracommunity and component community levels, indicating different responses by each helminth species to the environmental gradient.

The fauna and community structure of the helminths of two sympatric sigmodontine rodent hosts, Akodon montensis (Thomas, 1913) and Oligoryzomys nigripes (Olfers, 1818) (Rodentia, Cricetidae) were studied in two areas of an Atlantic Forest reserve, the Serra dos Órgãos National Park in Petrópolis and Teresópolis municipalities, state of Rio de Janeiro, Brazil. During the study, 127 rodents were collected, among which 63 were parasitized (approximately 50%). The helminths recovered from A. montensis were the nematodes Protospirura numidica criceticola, Stilestrongylus aculeata, Stilestrongylus eta, Stilestrongylus lanfrediae and Trichofreitasia lenti; the trematode Canaania obesa and the cestode Rodentolepis akodontis. Oligoryzomys nigripes was infected by Avellaria sp., Guerrerostrongylus zetta, T. lenti and S. lanfrediae. Complete host specificity was observed in all helminth species only in Petrópolis; although T. lenti and S. lanfrediae were shared between host species in Teresópolis. Stilestrongylus aculeata, S. eta and S. lanfrediae had the greatest abundance, i.e. considering all hosts, and intensity, i.e. considering only infected hosts, in the study. Stilestrongylus lanfrediae and G. zetta were the most prevalent species. Guerrerostrongylus zetta and S. lanfrediae had higher abundance and prevalence in adult hosts. The latter species also had higher abundance and prevalence in male hosts. Stilestrongylus aculeata and S. eta had higher prevalence in young female hosts, and T. lenti, higher abundance in males and higher prevalence in adult females of A. montensis. Only the helminth community of O. nigripes in Teresópolis followed a nested pattern of species distribution. All the other helminth communities in A. montensis and O. nigripes had random patterns of species distribution. The results suggest the existence of intrinsic characteristics between hosts and parasites as well as different patterns of associations in those interactions with the environment.