First report of Nematomystes scapteromi ( Ganzorig , Oku , Okamoto , Malgor & Kamiya , 1999 ) Jiménez-Ruiz & Gardner , 2003 ( Nematoda , Aspidoderidae ) in Scapteromys tumidus Waterhouse , 1837 ( Rodentia , Sigmodontinae ) from southern Brazil

Prior to the present study, Nematomystes scapteromi (Ganzorig, Oku, Okamoto, Malgor & Kamiya, 1999) Jiménez-Ruiz & Gardner, 2003 had been reported in Scapteromys tumidus Waterhouse, 1837 from Uruguay. Here, eight specimens of S. tumidus were collected in southern Brazil and necropsied. The nematodes encountered were determined as N. scapteromi through their morphometric traits. Prevalence was 87.5% and the mean intensity of infection of 18.3 helminths/host. This is the first report of N. scapteromi parasitizing S. tumidus in the state of Rio Grande do Sul, Brazil.

The genus Nematomystes Sutton, Chabaud & Durette-Desset, 1980 was proposed to accommodate Nematomystes rodentiphilus Sutton, Chabaud & Durette-Desset, 1980 due the presence of three lips with lateral projections, and the covering of the interlabial space by a V-shaped cuticular expansion (Sutton et al. 1980).Jiménez-Ruiz and Gardner (2003) emended the diagnosis of Nematomystes with a more detailed description of its characteristics, including those utilized to compare and distinguish the species of the family Aspidoderidae Skrjabin & Schikhobalova, 1947.The authors redescribed N. rodentiphilus and transferred Ansiruptodera scapteromi Ganzorig, Oku, Okamoto, Malgor & Kamiya, 1999 to Nematomystes, resulting in the inclusion of two valid species in the genus -N.rodentiphilus and N. scapteromi.
A number of helminths have been reported in  1975) and Isthmiophora scapteromae Sutton, 1983 in Argentina (Sutton 1983) and the nematode N. scapteromi in Uruguay (Ganzorig et al. 1999).In addition to Argentina and Uruguay, Waterhouse's Swamp Rat, S. tumidus, is known to occur in the state of Rio Grande do Sul, Brazil (Musser and Carleton 2005).This rodent feeds on plants, insects, and oligochaetes, including larvae that they capture by burrowing into the soil (Barlow 1969;Oliveira and Bonvicino 2006).This region (Argentina, Uruguay, and the State of Rio Grande do Sul) coincides with the Pampa biome, an important biological domain, with a range of endemic fauna and endangered species (Roesch et al. 2009).Ongoing expansion of monocultures and pasture and the introduction of exotic species have led to increasing degradation of the biome, resulting in the loss of biodiversity, including that of the local helminths.Considering that S. tumidus occurs only in this biome, data on its helminth fauna may provide important insights into the ecology of the species.This study provides the first report of N. scapteromi from southern Brazil.
All measurements are given in micrometers (μm), unless otherwise indicated, and are presented as in Gallas and Silveira (2013).Ecological terminology followed Bush et al. (1997).Illustrations were produced using a drawing tube attached to a microscope.The systematics and determination of the helminths followed Chabaud (2009) and Gibbons (2010).Representative specimens of the hosts were deposited in the 'Coleção de Vertebrados' (MCNU) of the 'Museu de Ciências Naturais da ULBRA', while specimens of the nematodes were deposited in the 'Coleção Helmintológica' (CHMU) of the same museum, in Canoas, Brazil.
Males measurements (n = 10).Body 4.23-5.63mm  The nematode specimens recovered in the present study were determined as N. scapteromi due to the presence of three lips, interlabia separated from the lips by a V-shaped cuticular expansion, and the morphometric data (Ganzorig et al. 1999;Jiménez-Ruiz and Gardner 2003).The specimens presented measurements similar to the specimens examined by Ganzorig et al. (1999).However, despite the fact that body length was similar, the specimens examined here presented a nerve ring that was more distant from the anterior end, small spicules and gubernaculum, and much smaller lateral alae on the females than those on the specimens studied by Ganzorig et al. (1999).
Prior to the present study, N. scapteromi was reported only in three S. tumidus specimens from Uruguay with a prevalence of 100% and an intensity of infection of five to 36 helminths (Ganzorig et al. 1999).In the present study, a prevalence of 87.5% was recorded in the eight S. tumidus specimens from Brazil, with an intensity of infection of one to 40 helminths.The relatively high prevalence and intensity of infection recorded for N. scapteromi in both studies may be related to the habitat and diet of the S. tumidus.In addition, the nematodes of the superfamily Heterakoidea Railliet & Henry, 1914 have a monoxenous cycle with the infection of the definitive hosts occurring through the ingestion of eggs containing infective larvae found in the environment inhabited by the host (Anderson 2000).
The present study provides the first report of N. scapteromi from the state of Rio Grande do Sul, Brazil, extending the known distribution of the species north and west of Uruguay (Ganzorig et al. 1999).As S. tumidus is known to occur only in the Pampa biome (Musser and Carleton 2005), the present study provides an important expansion of the range of N. scapteromi in this biological domain.