New locality records for Guerrerostrongylus zetta ( Travassos , 1937 ) Sutton & Durette-Desset , 1991 ( Nematoda : Heligmonellidae ) parasitizing Oligoryzomys nigripes ( Olfers , 1818 ) ( Rodentia : Sigmodontinae ) from southern Brazil

Guerrerostrongylus zetta had been found in a number of different species of rodents from northern and southeastern Brazil as well as Argentina. Between 2008 and 2010, specimens of Oligoryzomys nigripes (n = 14) were collected and necropsied. The nematodes encountered were identified as G. zetta due their morphological traits. Prevalence was 78%, with a mean intensity of infection of 5.63 helminths/host. This report fills in a lacuna in the known distribution of G. zetta, and provides the first record of this parasite in the state of Rio Grande do Sul, Brazil.

The family Cricetidae Fischer, 1817 includes the subfamily Sigmodontinae Wagner, 1843 that encompasses 74 genera and 236 species (Musser and Carleton 2005).Cricetids are found in a variety of habitats around the world and may present terrestrial, arboreal, fossorial, saltatorial or semi-aquatic habits as an adaptive response to the different environments they inhabit (Silva 1984).At least 21 species of sigmodontine rodents are known to occur in the state of Rio Grande do Sul, southern Brazil (Christoff et al. 2013).
Two species of Oligoryzomys Bangs, 1900 are found in Rio Grande do Sul (Christoff et al. 2013), Oligoryzomys flavescens (Whaterhouse, 1837) and Oligoryzomys nigripes (Olfers, 1818).Oligoryzomys nigripes is considered to be a scansorial, primarily nocturnal species found in open areas or forests of all the major types of vegetation found in Rio Grande do Sul (Christoff et al. 2013).The species is typically herbivorous, complementing its diet with invertebrates, such as the larvae of lepidopterans, coleopterans and hemipterans (Barlow 1969;Christoff et al. 2013).

Guerrerostrongylus zetta
All measurements are given in micrometers (μm), unless otherwise indicated.The number of specimens measured for a specific character only appears between parentheses when it was not possible to measure all the specimens, and the measurements are indicated as in Gallas and Silveira (2013).Ecological terminology follows Bush et al. (1997).The line drawings were prepared using a drawing tube and the photomicrographs were taken with a camera attached to the microscope.The systematics and determination of the helminths followed Durette-Desset ( 2009) and Gibbons (2010), and the identification of the host was based on Christoff tending to 1-3-1.Females monodelphic, with vulva next to the anus, conic tail, without spine.
The genus Guerrerostrongylus was proposed by Sutton and Durette-Desset (1991) Sutton and Durette-Desset (1991), based on the diagnostic traits of the genus.Guerrerostrongylus is currently known to include four species: Guerrerostrongylus gomesae Simões, Santos & Maldonado-Júnior, 2012, G. uruguayensis, Guerrerostrongylus ulysi Digiani, Notarnicola & Navone, 2012, and G. zetta (Digiani et al. 2012;Simões et al. 2012b).Differences among the species include the number and size of the ridges in the synlophe, the morphology of the causal bursa, in particular the dorsal and rays 6 and 8, and the morphology and length of the spicules (Sutton and Durette-Desset 1991;Digiani et al. 2012;Simões et al. 2012b).The nematodes retrieved in the present study all presented the morphological traits of G. zetta, as redescribed by Digiani et al. (2012).
There is some controversy over the spelling of the epitet specific -whether zetta or zeta is correct -but in the present study, the zetta form, used by Digiani et al. ( 2012) was adopted.With the exception of the body length of the males (6.6-10.7 mm) and females (10.2-17.9mm), the measurements recorded for G. zetta in the present study were similar to those reported by Vicente et al. (1997), Digiani et al. (2012) and Simões et al. (2012b).
Ecological parameters of G. zetta available in the literature were compared with data from the present study (Table 1).These values suggest that G. zetta may be considered a dominant species in the helminth fauna of O. nigripes, as suggested by Digiani et al. (2012) in Argentina, a characteristic also recorded in southeastern Brazil by Simões et al. (2011Simões et al. ( , 2012a) ) and now reported in southern Brazil, in the present study.
Guerrerostrongylus zetta has the broadest known geographical distribution of any Guerrerostrongylus species, and is the only species known to infect a number of different hosts (Digiani et al. 2012;Simões et al. 2012a).In the present study, G. zetta is reported for the first time from Rio Grande do Sul, in southern Brazil.However, as discussed above, there is a controversy over the identity of the type host of G. zetta, reinforcing the need for the identification of the host in any reports of the occurrence of these parasites.The identification of the host is normally facilitated by the use of appropriate identification keys or consultations with taxonomic specialists, to ensure the avoidance of incomplete or inconsistent reporting.Similarly, Digiani et al. (2012) considered that some published reports of G. zetta lack adequate descriptions or illustrations, and require systematic confirmation.These unconfirmed reports and the possible incorrect identification of hosts need to be rectified if the understanding of the diversity and distribution of the parasites of rodents and other vertebrates is to advance reliably.

ACKNOWLEDGEMENTS
DFW thanks the Research Foundation of the State of Rio Grande do Sul (FAPERGS) and the Scientific and Technological Initiation Program of the Lutheran University of Brazil (PROICT/ULBRA) for financial support.We thank the Laboratory of Mammal Systematics (ULBRA) for the donation of the hosts and Professor Stephen C. Ferrari (UFS) for reviewing the English text.

Table 1 .
Comparison of the ecological parameters of G. zetta in rodents.
* the number of hosts examined was not stated.