Distribution extension of Syphacia ( Seuratoxyuris ) peromysci Harkema , 1936 ( Nematoda , Syphaciinae ) parasitizing the Rock Mouse , Peromyscus difficilis ( J . A . Allen , 1891 ) ( Rodentia , Neotominae ) in central Mexico

As a part of an ongoing project in order to inventory the helminth parasites of rodents in Mexico, 49 individuals of Syphacia (Seuratoxyuris) peromysci were collected from five specimens of the Rock Mouse Peromyscus difficilis caught in Veracruz state, Mexico. This is the first report of S. peromysci in a Mexican endemic rodent, widening the known distribution of the species to the southern portion of the country.

Basin of central Mexico.
Between June, 2007 andJuly, 2008, five specimens of P. difficilis were caught under permit FAUT-0002 (issued to F. A. Cervantes) 3 km south of El Frijol Colorado (19°34ʹ20ʺ N, 097°23ʹ00ʺ W), Municipality of Perote, Veracruz, México, 2,437 m above sea level.The collecting and processing of rodents followed the guidelines of the American Society of Mammologists for use of wild animals in research (Kelt et al. 2010;Sikes et al. 2011).The intestine of hosts was examined for helminths under microscope; nematodes recovered were washed in 0.85% saline solution, and fixed in 4% hot formalin.For morphologic study, nematodes were cleared with Amman's lactophenol.All measurements are given in micrometers (µm) unless otherwise indicated.Measurements are recorded as the range followed by the mean and standard deviation in parentheses.For scanning electron microscopy (SEM) study, nematodes were dehydrated in series of gradual ethyl alcohol and critical point dried with carbon dioxide.Specimens were coated with a gold-palladium mix-ture and examined in a Hitachi Stereoscan Model SU 1510 at 10kV.Parasite voucher specimens were deposited at Colección Nacional de Helmintos (CNHE), Instituto de Biología, Universidad Nacional Autónoma de México (IBUNAM), Mexico City.Harkema, 1936 Description based on 49 specimens (25 males and 24 females) identified as S. peromysci (CNHE 5671) recovered from the caecum of one specimen of P. difficilis.
Our specimens were included in the subgenus Seuratoxyuris by having cephalic plate round, oval and laterally elongated in females, and a submedian papillae located in the first or second third to half of cephalic plate (measuring from position of amphids); in addition, the cuticle have characteristic superficial pattern (alternating parallel rings and perpendicular ridges); the accessory hook of gubernaculum presents ornamentations covering its entire surface, and the tail is short and conical in males.Seuratoxyuris differs of Syphacia and Cricetoxyuris by the morphology of cephalic plate (circular and quadrangular, respectively).Other traits that allow differentiating Seuratoxyuris is the presence of a lateral alae vestigial or absent in females, while in Syphacia and Cricetoxyuris the lateral alae is well developed.(Hugot 1988;Hugot et al. 2013;Robles et al. 2014).
Syphacia peromysci was described by Harkema (1936) as parasite of Peromyscus leucopus in North Carolina, USA.Since then, this taxon has been recorded in several species of Peromyscus (P.gossypinus, P. leucopus, P. maniculatus, and P. polionotus;Dyer 1969;Grundman et al. 1976;Kinsella 1991;Luong et al. 2013;Quentin and Kinsella 1972) also in USA.In Mexico this species has been recorded in P. maniculatus in Hidalgo (Pulido-Flores et al. 2005).
On the other hand, some rodent species kept in pet shops, have been reported as host of S. peromysci: Acomys cahirinus, Mesocricetus auratus, and Pachyuromys duprasi (Hasegawa et al. 2008).The presence of this nematode species in such rodents is of special interest, because apparently, pet breeders' facilities provide suitable conditions for host capture by pinworms, which may seldom occur under natural conditions.The presence of S. peromysci in Reithrodontomys megalotis and Xerospermophilus spilosoma, reported by Frandsen and Grundmann (1947) and Ubelaker et al. (2010), respectively, can be attributed to behavioral habits of rodents who build their nests in abandoned burrows (Villa and Cervantes 2003).
We report some variations in selected traits of females analyzed in this study regarding previous reports; for example, distance from vulva to anterior region in our specimens is shorter (187-412), than those recorded by Harkema (1936) and Kruidenier et al. (1961) (507-700).Similarly, females examined by Quentin and Kinsella (1972) have a total length of 4.0 mm opposite to 0.895-2.3475mm recorded in the Mexican material; females recorded by Harkema (1936) and Kruidenier et al. (1961) measure 2.0-3.2mm.However, we consider these traits just as intrinsic variability of the species because the diagnostic characteristics of this species are: the cephalic plate morphology in male and female as well as the number of ornamentations on accessory hook of gubernaculum.
The present study provides the first report of S. peromysci in an endemic rodent from Mexico, expanding the known distribution range of the species south of the country.

ACKNOWLEDGEMENTS
The authors thank Berenit Mendoza-Garfias for her technical assistance with scanning electron microscopy.This study was partially funded by a research grant "Apoyo a la Incorporación de Nuevos PTC", PROMEP-SEP to JFO.