Pathologies of Oligacanthorhynchus pardalis (Acanthocephala, Oligacanthorhynchidae) in Leopardus tigrinus (Carnivora, Felidae) in Southern Brazil

In Brazil, Oligacanthorhynchus pardalis (Westrumb, 1821) Schmidt, 1972 has been observed in five species of wild felines. In the present study, five roadkilled oncillas (Leopardus tigrinus Schreber, 1775) were collected in the State of Rio Grande do Sul, Brazil. Chronic lesions caused by O. pardalis were observed in the small intestine of one of the specimens. Histological examination identified a well-defined leukocyte infiltration and an area of collagenous fibrosis. Only males parasites (n = 5) were found, with a prevalence of 20%. The life cycle of Oligacanthorhynchus species is poorly known, although arthropods may be their intermediate hosts. The low prevalence encountered may be related to the small number of hosts examined, and the reduced ingestion of arthropods infected by larvae of O. pardalis. This is the first report of O. pardalis parasitizing L. tigrinus in the Brazilian state of Rio Grande do Sul.

Acanthocephalan species cause damage to their hosts in the area where the proboscis is attached, which may cause formation of nodules, granulomas and inflammations, and may predispose towards secondary infections (NICKOL, 1985;RICHARDSON;BARNAWELL, 1995;KENNEDY, 2006).Babero (1957) and Richardson and Barnawell (1995)  This study characterizes the lesions caused by O. pardalis through histological sections from a specimen of L. tigrinus obtained in the Brazilian state of Rio Grande do Sul.

Materials and Methods
Between 2008 and 2010, five roadkilled adult specimens of L. tigrinus were collected from highways in the Brazilian state of Rio Grande do Sul.These specimens were donated to the "Laboratório de Zoologia dos Invertebrados" at "Museu de Ciências Naturais da ULBRA", MCNU, for necropsy.The acanthocephalans encountered were processed according to the techniques described by Amato and Amato (2010).Ecological terms were utilized according to Bush et al. (1997).Morphometric measurements are presented as means with ranges and standard deviations and the number of specimens measured (n) is given in parentheses.All measurements are given in micrometers, unless otherwise indicated.
Drawings were made with a drawing tube on a microscope.For histological processing, the sample was dehydrated in a graded series of xylene/ethanol before being embedded in a paraffin block.Histological sections of thickness 5 µm were stained according to the method of Luna (1968).The parasite species was identified according to the classification of Amin (1985) and the host species, based on Wozencraft (2005).A representative specimen was deposited in the "Coleção Helmintológica do Instituto Oswaldo Cruz", CHIOC, Rio de Janeiro, Brazil.
One specimen was fixed in situ in the intestine, with free trunk and lesions of diameter 1 mm (n = 7), representing the proboscis attachments (Figure 2a).Macroscopic alterations of the serous layer consisting of nodules of 3.5 to 6.0 mm in diameter and 2 to 4 mm in height, corresponded to the sites at which the proboscis was attached to the lumen (Figure 2b).Microscopic alterations were observed in the mucosa, submucosa, and muscularis layers, which were affected by the proboscis attachment.The analysis identified a leukocytic infiltration between the submucosa and muscularis layers (Figure 2c).The area adjacent to this infiltration was characterized by coarse, fibrous collagen in a disorderly arrangement, with abundance of fibroblasts and fibrocytes (Figure 2d).

Discussion
In acanthocephalans, the sex ratio (1:1) is determined at fertilization (CROMPTON, 1985).Exclusive occurrence of male specimens may provoke competition among the O. pardalis males, thus resulting in changes to body and testis size (SASAL et al., 2000).
The lesions found in the present study are closely similar, in terms of nodule length and damage to the tissue layers, to those reported for O. tortuosa (BABERO, 1957;RICHARDSON;BARNAWELL, 1995).Babero (1957) observed red nodules, which Richardson and Barnawell (1995) interpreted as the result from hemorrhaging caused by the attachment of the parasite.Absence of hemorrhaging and absence of polymorphonuclear leukocytes (PMN) are indicative of the chronic inflammation induced by O. pardalis, as reported in relation to O. torturosa by Richardson and Barnawell (1995).
The advanced state of putrefaction of the oncilla specimen impeded a more detailed analysis of the lesions.In particular, atrophic processes and necrotic abscesses, as reported by Babero (1957) and Richardson and Barnawell (1995), were not observed.The extensive fibrosis associated with leukocytic infiltration indicates that the parasites do not migrate after attachment (RICHARDSON; BARNAWELL, 1995).In the present study, the presence of fibrosis indicates that the acanthocephalans did not migrate after attachment of their proboscises to the lumen of L. tigrinus.However, the number of lesions (n = 7), together with the number of O. pardalis specimens encountered (n = 5) also indicates that some specimens migrated before definitive attachment and formation of the fibrosis.
The first study on the life cycle of an Oligacanthorhynchus species was conducted by Richardson (2006).The diplopod Narceus americanus Palisot de Beauvois, 1817, has been identified as an intermediate host of O. tortuosa.Ingestion of rodents, lizards, birds, and arthropods by L. tigrinus has been documented by Sunquist and Sunquist (2002).The low infection rates found in the present study may be related to the small number of hosts analyzed and the low ingestion of arthropods infected with the larvae of O. pardalis.Vieira et al. (2008) recorded O. pardalis as a parasite of only four feline species, L. pardalis, L. geoffroyi, P. onca, and Pu.concolor.However, their study overlooked Travassos (1917), who identified L. tigrinus from São Paulo, Brazil, as a definitive host of O. pardalis.The present study is the first record of O. pardalis parasitizing L. tigrinus in the Brazilian state of Rio Grande do Sul.
described the lesions caused by Oligacanthorhynchus tortuosa (Leidy, 1850) Schmidt, 1972 in opossums in the United States, but no data are available on the lesions caused by other Oligacanthorhynchus species.