Among the Brazilian marsupials, the species of the genus Didelphis are the most parasitized by helminths. This study aimed to describe the species composition and to analyse the helminth communities of the Atlantic Forest common opossum Didelphis aurita at infracommunity and component community levels using the Elements of Metacommunity Structure Analysis, considering peri-urban, sylvatic and rural environments in the state of Rio de Janeiro, Brazil. Seventy-three specimens of D. aurita were captured during the study. Fourteen species of helminths were collected: nine of the phylum Nematoda (Trichuris minuta, Trichuris didelphis, Globocephalus marsupialis, Heterostrongylus heterostrongylus, Travassostrongylus orloffi, Viannaia hamata, Aspidodera raillieti, Cruzia tentaculata and Turgida turgida); four of the phylum Platyhelminthes (three species of Trematoda, Duboisiella proloba, Brachylaima advena and Rhopalias coronatus, and one species of the class Cestoda); and one species of the phylum Acanthocephala (Oligacanthorhynchus microcephalus). More than 95% of the animals were infected with parasites. The most abundant parasite species were V. hamata, T. turgida, C. tentaculata and T. orloffi. The nematodes T. turgida, C. tentaculata and A. raillieti were the most dominant species in the three environments. The analysis of the metacommunity structure indicated a structured pattern as a function of the environmental gradient, but only when all localities were considered together. At the infracommunity and component community levels, quasi-nested and nested structures with stochastic species loss were observed, respectively. The results indicate that the settlement of helminth species in the opossums can be attributed to the heterogeneity among individual hosts in relation to their exposure to parasites and to extrinsic factors, which vary among habitats, considering a regional scale. On a local scale, the characteristics of this host species may promote homogenization among individual hosts in terms of their exposure to the helminths. This study constitutes a new host record for the species G. marsupialis and T. didelphis and represents a pioneering investigation of the helminth metacommunity of a Neotropical marsupial.

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Ecological studies of host-parasite interactions are common in rodents. However, despite the widespread occurrence of endoparasites in those animals, there is a lack of information about the community structure of these parasites. The aims of this study were to describe the species composition and the community structure of helminths of the rodents Oligoryzomys nigripes, Akodon montensis and Euryoryzomys russatus (Rodentia, Sigmodontinae), and to investigate the influence of host species, age and gender on the abundance and prevalence of helminths. The pattern of the metacommunity structure of the helminths of A. montensis was also analysed. Small mammals were captured in Serra do Tabuleiro State Park, Santo Amaro da Imperatriz, state of Santa Catarina, Brazil. Helminths were identified and counted. Each species had its abundance, intensity and prevalence estimated for each host. The influence of host species, age and gender on abundance and prevalence of helminths was tested using generalized linear models (GLM). The metacommunity was analysed by calculating the Elements of Metacommunity Structure (EEM) for infracommunities. In O. nigripes, the species Guerrerostrongylus zetta and Stilestrongylus lanfrediae (Nematoda, Heligmonellidae) were found. A. montensis harboured G. zetta, Trichofreitasia lenti (Nematoda, Heligmonellidae), Trichuris navonae (Nematoda, Trichuridae), Angiostrongylus sp. (Nematoda, Angiostrongylidae), Litomosoides chagasfilhoi (Nematoda, Onchocercidae) and Rodentolepis akodontis (Plathyhelmintes, Cestoda). In the E. russatus rodent, the species G. zetta, Stilestrongylus rolandoi (Nematoda, Heligmonellidae) and Raillietina guaricanae (Plathyhelmintes, Cestoda) were found. This study presented new records of the helminths S. rolandoi and R. guaricanae in E. russatus, and of L. chagasfilhoi in A. montensis. The helminth metacommunity structure of A. montensis presented a random pattern of species distribution, characterized by a non-coherent structure along the environmental gradient, indicating different environmental requirements due to the infection of this host by helminths with different life cycles.

Despite the widespread occurrence and the great number of studies of the common opossum Didelphis aurita (Didelphimorphia, Didelphidae), there is a serious lack of information about helminth parasitism in these species. The synanthropic characteristic of these animals may influence their parasite fauna and the ecological parameters. We evaluated the abundance, intensity, prevalence and spatial aggregation of the most abundant nematodes of the large intestine and stomach, recovered from the common opossum D. aurita, in Pedra Branca State Park and its surroundings, which includes the FIOCRUZ Atlantic Forest Campus, Rio de Janeiro, Brazil. We investigated the effects of anthropic disturbances on the helminth populations comparing the parameters in relation to host habitat types, season and host gender in order to understand the ecological host-parasite interaction. The animals were sampled in three different habitats. We conducted eight small mammal samplings in different seasons and collected 48 individuals of the common opossum. The nematode species found in the large intestine were Aspidodera raillieti and Cruzia tentaculata while Turgida turgida was found in the stomach. Cruzia tentaculata was the species with the highest abundance, intensity and prevalence indices. The three species had a highly aggregated distribution. No species had significant difference in prevalence when compared with host habitat types, host gender or season. Cruzia tentaculata had higher intensity in the rainy season, which suggests that rainfall contributes to the development of the life cycle of this helminth. Turgida turgida had higher abundance in the disturbed forest habitat, suggesting that the presence of intermediate hosts may be favoured by the characteristics of this environment.

A new species of Nippostrongylinae (Nematoda: Heligmonellidae), Stilestrongylus rolandoi n. sp., is described from specimens collected from the small intestine of the rodent Euryoryzomys russatus in the Atlantic Forest (Santo Amaro da Imperatriz, Santa Catarina state, southern Brazil). The genus Stilestrongylus includes 23 species, which parasitize rodents occurring in the Neotropical region. Stilestrongylus aureus (Durette-Desset & Sutton, 1985) from Argentina, S. azarai (Durette-Desset & Sutton, 1985) from Argentina, S. flavescens (Sutton & Durette-Desset, 1991) from Uruguay, S. franciscanus (Digiani & Durette-Desset, 2002) from Argentina, S. gracielae (Digiani & Durette-Desset, 2006) from Argentina, and S. oryzomysi (Sutton & Durette-Desset, 1991) from Argentina are closely related to Stilestrongylus rolandoi n. sp., all having caudal bursa patterns of types 1-4 in one of the lobes. Stilestrongylus rolandoi n. sp. is distinguished from the aforementioned species by its ray 6 being short in relation to rays 4 and 5, which are long and robust, and by having caudal bursa patterns of types 1-4 in both lobes. The new species has 27 ridges in the mid-body in males, and 24 in females, and has one of the highest ratios of spicule length to body length (21-33%) in this genus.

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