Introduction

Dioctophyme renale (Goeze, 1782) infection occurs in many countries worldwide including domestic dogs and cats and also in wild carnivores such as canids and mustelids. The preferred organ site of D. renale infection is the right kidney. However, there are several reports describing the presence of the nematode in the peritoneal cavity and, less frequently in both kidneys from the same animal and in other sites throughout the body ( ^{ANDERSON, 2000} ). This parasitic disease is of public health interest since it is a zoonosis and therefore poses a risk to humans. In Asian countries, there are case reports of dioctophymatosis in humans in which D. renale was found in the skin and the kidneys of the affected individuals ( ^{HANJANI et al., 1968} ; ^{URANO et al., 2001} ; ^{IGNJATOVIC et al., 2003} ; ^{KATAFIGIOTIS et al., 2013} ; ^{TOKIWA et al., 2014} ; ^{NOROUZI et al., 2017} ). In Brazil, to date there is only one case of D. renale infection affecting a person in the state of Maranhão ( ^{LISBOA, 1945} ).

The life cycle of the nematode involves freshwater organisms such as oligochaetes which are the intermediate hosts, fish, and anurans that play the role of paratenic hosts. These aquatic organisms may harbor the infective third-stage larva which is transmitted to mammalian definitive hosts along the food chain. Once in the final host, the worm migrates to the kidney and completes its life cycle. Third-stage larvae develop into adults, and the female starts laying eggs which are shed in the urine contaminating the environment ( ^{MACE & ANDERSON, 1975} ; ^{MEASURES & ANDERSON, 1985} ).

In Brazil, larvae of D. renale have been found in anurans ( ^{PEDRASSANI et al., 2009} ), fish ( ^{ABDALLAH et al., 2012} ; ^{MASCARENHAS et al., 2016} ), and freshwater turtles ( ^{MASCARENHAS & MÜLLER, 2015} ; ^{MASCARENHAS et al., 2017} ). Three of these cases of D. renale infection affecting aquatic organisms in Brazil ( ^{MASCARENHAS & MÜLLER, 2015} ; ^{MASCARENHAS et al., 2016} ; ^{MASCARENHAS et al., 2017} ) originated from the southern region of the State of Rio Grande do Sul, where several cases of dioctophymatosis have been diagnosed in dogs ( ^{RAPPETI et al., 2017} ). The present report documents the occurrence of D. renale larvae in a previously unreported host from southern Brazil.

Materials and Methods

Three specimens of Philodryas patagoniensis (Girard, 1857) (Serpentes: Dipsadidae) (common names in Brazil: “parelheira”, “papa-pinto”) roadkill in the county of Capão do Leão, State of Rio Grande do Sul, southern Brazil, were necropsied. Sample collection was authorized by the Instituto Chico Mendes de Conservação da Biodiversidade (ICMBio/n° 38913).

At necropsy, the following organs from these snakes were examined individually: oral cavity, esophagus, stomach, small intestine, large intestine, heart, liver, lungs, kidneys, gonads, and coelomic cavity.

Larvae were fixed in AFA, stored in 70° alcohol GL, and clarified with Amann lactophenol. Larvae of D. renale were morphologically identified according to ^{Mace & Anderson (1975)} and ^{Measures & Anderson (1985)} .

Specimens were deposited in the Coleção de Helmintos do Laboratório de Parasitologia de Animais Silvestres (CHLAPASIL/UFPel, Pelotas, RS, Brazil, nº 713). Photomicrographs were captured using an Olympus® BX 41 microscope with a camera. The software Adobe Photoshop®CS5 was used to prepare the images for publication.

Results and Discussion

One specimen of P. patagoniensis were parasitized by two third-stage larvae of D. renale ( Figure 1 ). Larvae were reddish in color and were found encysted in the coelomic cavity of this snake. Measurements of male and female larvae of D. renale are given in Table 1 .

Figure 1 Third-stage larva of Dioctophyme renale parasite of Philodryas patagoniensis (Girard, 1858) (Serpentes: Dipsadidae) from southern Brazil. A – Anterior extremity of female larva (es – esophagus) (Bar = 60 µm). B – Posterior extremity of female larva (Bar = 62 µm). C – Vulvar primordium (arrows) of female larva near to junction esophagus-intestine (es – esophagus, in – intestine) (Bar = 95 µm). D – Detail of vulvar primordium (arrow) and intestine (in) of female larva (Bar = 95 µm).  

^{Biserkov (1995)} and ^{Yildirimhan et al. (2007)} reported the occurrence of larvae of Dioctophymatidae in snakes from Bulgaria and Turkey, where larvae of Eustrongylides excisus Jagerskiold, 1909 was reported in Natrix tessellata (Laurenti, 1768) (dice snake) and Natrix natrix (Linnaeus, 1758) (grass snake) (Natricidae). Morphological differentiation between third-stage larvae of D. renale and Eustrongylides spp. is made mainly by the position of the vulvar primordium in the female larvae. In female larvae of D. renale, the vulvar primordium is located near the intestinal-esophageal junction ( ^{MACE & ANDERSON, 1975} ; ^{MEASURES & ANDERSON, 1985} ), whereas in female larvae of Eustrongylides spp. this structure lies close to the anal aperture ( ^{MEASURES, 1988} ). Figure 1 CD shows the vulvar primordium near the intestinal-esophageal junction in the female larva of D. renale found in the snake.

In the State of Rio Grande do Sul (RS), southern Brazil, third-stage larvae of D. renale have been found in the freshwater turtles, Trachemys dorbigni (Duméril & Bibron, 1835) (D’Orbigny’s slider, “tartaruga-tigre”) and Phrynops hilarii (Duméril & Bibron, 1835) (Hilaire’s toadhead turtle) and in the catfish Hoplosternum littorale (Hancock, 1828). In the urban area of the city of Pelotas, south region of RS, which is located in the vicinity of the neighbor city Capão do Leão, there are reports on the occurrence of larvae of D. renale in T. dorbigni (Emydidae) with a prevalence of 87.5% and mean intensity of infection of 13.9 larvae/host in 32 necropsied freshwater turtles ( ^{MASCARENHAS & MULLER, 2015} ). The prevalence and mean intensity of infection in cases of parasitism by larvae of D. renale in P. hilarii (Chelidae) ( ^{MASCARENHAS et al., 2017} ) and H. littorale (Callichthyidae) ( ^{MASCARENHAS et al., 2016} ) were both low in comparison with those of T. dorbigni. It is worth mentioning that few specimens of P. hilarii e H. littorale were examined.

The life cycle of D. renale consists of complex trophic interactions in which mammalian definitive hosts are infected through ingestion of intermediate hosts (freshwater oligochaetes) or paratenic hosts (fish and anurans) which are infected with third-stage larvae of the nematode ( ^{MACE & ANDERSON, 1975} ; ^{MEASURES & ANDERSON, 1985} ). In the Brazilian cities of Pelotas and Capão do Leão the adult stage of D. renale occurs in domestic dogs, cats ( ^{RAPPETI et al., 2017} ) and in the wild carnivores Galictis cuja (Molina, 1782) (lesser grisson) ( ^{PESENTI et al., 2012} ), Lontra longicaudis (Olfers, 1818) (neotropical river otter) (Mustellidae) ( ^{ECHENIQUE et al., 2018} ), and Leopardus geoffroyi (d'Orbigny & Gervais, 1844) (Felidae) (Geoffroy’s cat) ( ^{TRINDADE et al., 2018} ).

The presence of larvae of D. renale in the snake P. patagonensis may be related to the feeding habit of this host which is a dietary generalist. Its diet includes include birds, amphibians, lizards, other species of snakes, and rodents ( ^{HARTMANN & MARQUES, 2005} ; ^{SAZIMA & HADDAD, 1992} ; ^{ROCHA & VRCIBRADIC, 1998} ). Despite the fact that snakes have a broad, generalist diet, ^{Pontes (2007)} reported that the diet of P. patagonensis which live along the coast of the State of Rio Grande do Sul, southern Brazil, consists mostly of anuran amphibians. Interestingly, anurans are paratenic hosts of D. renale in Canada ( ^{MACE & ANDERSON, 1975} ) and Brazil in the state of Santa Catarina ( ^{PEDRASSANI et al., 2009} ). In this context, the ocurrence of D. renale in snakes, freshwater turtles, and fish in our study area suggests that infective larvae of this nematode are transferred between different hosts that form the food web. Wild carnivores are the definitive hosts of this helminth and are at the top of the food chain. Potential paratenic hosts inhabit this geographic region and may contribute for the perpetutation of the life-cycle of this worm in wildlife.

The role of snakes, freshwater turtles, and fish as a source of infection for domestic dogs and maintenance of the life-cycle of the parasite in urban areas should be interpreted with caution, since these hosts must be ingested by the dogs for that occurs infection with the larvae. We should also consider the fact that it may be difficult for dogs to capture a sufficient number of vertebrate preys in urban areas in order to mantain effectively the life cycle of the helminth. However, we should not rule out the possibility that dogs may ingest freshwater turtles and snakes hit by cars in urban areas. Third-stage larvae of D. renale may be found in roadkill vertebrates hosts such as P. hilarii as described by ^{Mascarenhas et al. (2017)} . Our findings corroborate those of previous research published by these authors. We should emphasize the fact that the presence of larvae of D. renale in fish, freshwater turtles, and snakes indicates that these vertebrates may be sentinel species for the occurrence of dioctophymatosis in our area. From 2010 to 2015, about 70 cases of canine dioctophymatosis were diagnosed in the city of Pelotas, State of Rio Grande do Sul, southern Brazil ( ^{RAPPETI et al., 2017} ).

The results of the present study show that the south region of the State of Rio Grande do Sul is an important area of occurrence for D. renale infection in animals. In this scenario of several hosts that harboring the nematode, remains a gap to be known: the essential link that allows the continuity of the cycle, the intermediate host. The freshwater oligochaete Lumbriculus variegatus (Müller, 1774) (Lumbriculidae: Clitellata) was identified in North America as the intermediate host of D. renale larvae ( ^{MACE & ANDERSON, 1975} ). However, in South America the intermediate host in which the third-stage infecting larvae develop remains unknown. Lumbriculus variegatus has been found in Patagonia, Argentina ( ^{MISERENDINO, 2007} ) and in the State of Minas Gerais, southeast Brazil ( ^{MARCHESE et al., 2015} ). However, we should consider the hypothesis that other species of oligochaetes may also act as intermediate hosts of the worm in South America.

Dioctophymatosis is a parasitic disease that may threaten animal and public health. Additional studies should be conducted to investigate the life cycle of D. renale in our area. Further research should be carried out to determine the epidemiological aspects of the transmission and maintainance of the life cycle of this nematode in urban areas.