Introduction

Commercial breeding of wild boars in Brazil started in the late 1980s in the south with animals purchased from zoos and from Argentina. The meat was well accepted by consumers and the market expanded with the introduction of purebreds from France. Commercial farms currently exist in several Brazilian states (^{GIMENEZ et al., 2003}).

The breeding method most used in Brazil is the outdoor intensive rearing system. In this system, the animals are kept in outdoor paddocks, allowing them to express their natural behavior. However, this practice facilitates helminth infection, which impairs the development and reproductive potential of the animals due to easy access to intermediate hosts, paratenic hosts, eggs and larvae that are in the environment.

The availability of eggs and larvae in the environment and the abundance of intermediate hosts are directly influenced by temperature and humidity conditions, among other factors (^{JESUS; MÜLLER, 2000}). Therefore, it is important to investigate the dynamics of parasite populations in different climatic regions.

This study aimed to identify the helminths that inhabited the gastrointestinal tract of specimens of Sus scrofa scrofa at commercial breeding facilities in southern Brazil, and estimate parameters for the prevalence, mean intensity and mean abundance of parasitism.

Studies on the gastrointestinal helminth fauna of wild Sus scrofa scrofa have been carried out in several European countries (^{HUMBERT; HENRY, 1989}; ^{DE-LA-MUELA et al., 2001}; ^{RAJKOVIĆ-JANJE et al., 2002}; ^{FERNANDEZ-DE-MERA et al., 2003}; ^{JÄRVIS et al., 2007}; ^{SENLIK et al., 2011}), in Asia (^{ESLAMI; FARSAD-HAMDI, 1992}; ^{SATO et al., 2008}) and in North America (^{SHENDER et al., 2002}). However there are only a few studies relating to identification of gastrointestinal parasites in wild boars from commercial farms, and these were conducted in Poland (^{POPIOŁEK et al., 2010}) and in southeastern Brazil (^{MUNDIM et al., 2004};^{GOMES et al., 2005}). Only ^{Gomes et al. (2005)} performed morphological identification on adult parasites recovered through necropsy, while the others authors made diagnoses only through detection of eggs in fecal examinations. In addition, all previous studies were undertaken in tropical or temperate regions, unlike southern Brazil, which has a subtropical climate. This factor directly affects the helminth infection parameters, and also leads to different management on each farm, particularly for animals reared outdoors.

Materials and Methods

Digestive systems were collected from 40 wild boars aged between seven and eight months, during slaughter in a cold-storage slaughterhouse. There were two collections of 20 gastrointestinal tracts each, the first in August 2010 and the second in May 2011.

The wild boars were from a commercial breeding facility situated in the city of Antônio Prado, in the northern part of the state of Rio Grande do Sul, Brazil (28° 51′ 28″ S and 51° 16′ 58″ W), which has a subtropical climate with an average annual temperature of 15 °C. The number of animals per paddock varied between 50 and 60 individuals, all from the breeding farm itself. Regarding the use of anthelmintics, after weaning (at the age of approximately 60 days), 1% ivermectin was used together with the feed daily, every month during the spring and summer, and every second month in the fall and winter (i.e. it was used for a month and paused for the next month).

The stomach and intestine were opened individually under running water in buckets, and the contents were washed in 500 µm and 150 µm sieves. The material retained in the sieve was stored in bottles for later identification, sexing, and counting of helminthes using a stereomicroscope. The esophagus and liver were directly examined under a stereomicroscope. The helminths were processed for identification in accordance with the techniques described by ^{Amato and Amato (2008)}. The parameters of mean abundance and mean intensity of parasitism were evaluated in accordance with ^{Bush et al. (1997)}.

Results and Discussion

A total of 87% of the 40 animals analyzed were parasitized by the following gastrointestinal helminths: Ascaris suum,Trichostrongylus colubriformis, Oesophagostomum dentatum and Trichuris suis (Table 1).

Trichostrongylus colubriformis showed a prevalence of 45% and mean intensity of 28.4, and was recorded for the first time parasitizing wild boars. This occurrence is also rare for domestic pigs, since T. colubriformisis more commonly found parasitizing the intestine of ruminants (VICENTE et al., 1997). In Brazil, T. colubriformis has been described parasitizing the small intestine of Sus domesticus in the states of Bahia and Goiás and in the Federal District (^{FREITAS; COSTA, 1962}; ^{COSTA, 1965}; ^{CARNEIRO et al., 1980}). The effects of parasitism by T. colubriformis in pigs have not been clearly studied; however, based on research on ruminants, higher intensity infections can cause loss of absorption and diarrhea, thus resulting in weight reduction (^{URQUHART et al., 1996}).

The data from this study show that T. colubriformis not only has a capacity to develop in the small intestines of wild boars, but also adapts well to wild rearing. This differs from modern pig farming, in which the animals are confined in a room with a concrete floor, which hinders larval development (the eggs hatch into L1 larvae which complete their development in soil until the L3 stage). In wild boar farming, in which the animals are kept in outdoor paddocks, the environment favors the development of these larvae and facilitates animal infection. Therefore, T. colubriformis represents a possible cause of economic loss in wild boar rearing, due to trichostrongylid resistance to the drugs available in the market (MOLENTO, 2004; ^{COLES, 2005}), and the survivability of larvae in the soil.

Furthermore, there have been sporadic reports of human infections withT. colubriformis (^{SATO et al., 2011}; ^{LATTÈS et al., 2011}). For this reason, breeders need to be attentive particularly regarding appropriate disposal of animal feces, because use of feces as fertilizer for home gardens can be a source of human infection (^{LATTÈS et al., 2011}).

Trichuris suis was present in 67.5% of the animals, and had the highest prevalence ever recorded in wild boars, considering animals bred both in captivity and in the wild. However, the mean intensity (178.1 ± 414.3) was lower than the level of 644.3 that was recorded by ^{Gomes et al. (2005)} in a breeding facility in the northwest of the state of São Paulo, Brazil. In other studies on wild boars, the mean intensity of infection previously described was lower than what was recorded in the present study. The highest intensity ever (117.67) was described by ^{Fernandez-de-Mera et al. (2003)} in wild boars in France. This may have been due to great availability of eggs within a small area in the breeding facilities, and also to egg resistance in the environment, where they may remain viable for up to four years (^{URQUHART et al., 1996}). T. suis also presented highly variable intensity (Table 1), such that some animals were infected with only a few parasites and others had a high degree of parasitism. These data coincide with findings from the state of São Paulo (^{GOMES et al., 2005}), and may be due to either lower resistance of the animals to infection with T. suis or possible resistance of the parasite to the anthelmintic used. A high infection rate can cause losses to wild boar rearing, because animals with a high intensity of infection can have serious intestinal disorders that impair their development.

Ascaris suum showed prevalence of 47.5%. Only 26.3% of the animals were parasitized by adult forms. Large variation in the intensity of larval infection and low intensities of adults (Table 1) are common among ascarids because of their population dynamics.A. suum seems to be highly immunogenic. A great quantity of larvae is expelled from the small intestine over a period of 14-17 days after infection. Larvae that remain in the organism migrate through the liver and lungs, because a large number of adult parasites of this species could cause the death of the animal, which would not be advantageous for the parasite (^{MIQUEL et al., 2005}; ^{NEJSUM et al., 2009}; ^{ROEPSTORFF et al., 2011}). This could explain the occurrence of larvae in the large intestine. However, occurrences of adults in this organ may be explained by parasite migration after host death due to adverse conditions in their habitat.

Among the helminths found, Oesophagostomum dentatum had the lowest prevalence (5.0%) and mean intensity (1.0), far below what was reported in the state of São Paulo by ^{Gomes et al. (2005)} (22.2% and 13.3, respectively). This variation can be attributed to the climates of these regions, due to the low survival of O. dentatum larvae in the soil during the hottest and driest summers and coldest winters (^{ROEPSTORFF; MURRELL, 1997};^{THOMSEN et al., 2001}; ^{ROEPSTORFF et al., 2011}). However, the presence of this parasite indicates that there is a potential risk because of the easy dissemination of eggs and larvae in the paddocks, and the difficulty in controlling this environment. Moreover, O. dentatum presents resistance to the drugs available in the market (^{COLES, 2005}). Except for O. dentatum, the other species in this report were recorded for the first time parasitizing wild boars in a subtropical region.