Salmonella sp. in Game ( Sus scrofa and Oryctolagus cuniculus )

Introduction

I n 2008, Salmonellosis cases in humans were the second most commonly reported zoonotic disease in the European Union (EFSA, 2010).

The importance of wildlife as Salmonella sp. carrier has been highlighted in several studies: on hedgehogs (Handeland et al., 2002), wild birds (Refsum et al., 2002), wild birds and mammals (Millán et al., 2004), and white-tailed deer (Renter et al., 2006). However, to date, knowledge on Salmonella sp. epidemiological distribution in wild boars and wild rabbits is very limited. In particular, regarding Portugal, no bibliographic references were found at all. Therefore, it is important to understand the role that game animals play as carriers of this zoonotic agent and how they could compromise control programs in use by veterinary authorities.

Considering the importance they have as the main game hunted in Portugal, determination of the prevalence of Salmonella sp. and serovars in hunted wild boars and wild rabbits was defined as the main objective of this study.

Materials and Methods

During the hunting season of 2005/2006 (December 2005–February 2006), hunting associations from Northern Portugal (41° 08′ N; 7° 54′ W to 41° 57′ N; 6° 34′ W) were contacted to collaborate in this study. The majority of associations did, in fact, participate in the study, allowing us to collect samples from a total of 77 hunted wild boars (Sus scrofa) and 80 wild rabbits (Oryctolagus cuniculus). For sampling, after each hunting campaign, the harvested animals were collected at a specific location where a rectal fecal sample from each animal was aseptically collected.

All the samples were analyzed by means of standard culture methods, according to the annex D of the ISO norm 6579:2002, and presumptive Salmonella isolates (1–2 colonies from each sample) were confirmed through biochemical tests, defined previously by Vieira-Pinto et al. (2005).

One Salmonella isolate was serotyped from each positive sample according to the Kauffmann-White scheme (Popoff, 2001) in the Laboratório Nacional Investigação Veterinária (LNIV)—National Reference Laboratory for Salmonella.

Results and Discussion

The present study showed that 22.1% of the (17/77) wild boar and 47.5% (38/80) of the wild rabbit presented Salmonella sp. in their feces (Table 1), highlighting their potential role as important carriers and spreaders of this zoonotic agent.

As mentioned above, no reports on the presence of Salmonella sp. in fecal samples of wild boars and wild rabbit were available, this study being the first observation of Salmonella sp. in fecal samples of these game species.

In this study, two serovars were identified in wild boar samples: Salmonella Typhimurium (64.7%) and Salmonella Rissen (35.3%). The predominant occurrence pattern of Salmonella Typhimurium in wild boar's fecal samples is reminiscent of a previous observation in domestic pigs in Portugal (Vieira-Pinto et al., 2005) and in Europe (EFSA, 2010). Also, in this study, S. Typhimurium was identified (15.8%) in fecal samples of wild rabbits. The data available from this study and from previous studies are not enough to prove the circulation of common Salmonella sp. strains between these animal populations. Nevertheless, the similarity in Salmonella serovar pattern prevalence between pig, wild rabbit, and wild boar population may indicate common infection sources and possible transmission between these animal species, which share common geographical areas and natural resources. It may be a particular feature of Northern Portuguese rural areas, where physical contact between wild boars and wild rabbits, and the increasing popularity of raising pigs outdoors are frequently reported.

Salmonella Typhimurium was the second most frequently identified Salmonella serovar in the European human salmonellosis cases reported in 2008 (EFSA, 2010) and should be under special attention due to its virulence to humans and to its high resistance rate to antibiotics (Crhuchaga et al., 2001). Also, from the other serovars identified in the wild rabbit's samples, special concern should be given to Salmonella Enteritidis (26.4%), since this was the Salmonella serovar most identified in the European human salmonellosis cases, and to Salmonella Derby (5.3%), which was included in the top 10 serovars reported in human cases in 2008 in Europe (EFSA, 2010). Human health risk from game infected with Salmonella sp. arises indirectly from agricultural areas and contamination of vegetable products, through direct animal contact, during hunting and carcass manipulation, or directly from ingestion of contaminated meat or meat products (Vengust et al., 2006). The contamination of wild boars' carcasses by feces and subsequent invasion by enteric pathogenic bacteria could easily be observed in game, since, in general, after being hunted, animals are eviscerated and skinned under insufficiently hygienic conditions (Decastelli et al., 1995).

The results observed in this study confirm the importance of wild boar and wild rabbit as carriers and fecal spreaders of pathogenic Salmonella serovars, which could represent a source of infection for animals (wild and domestic) and for humans.

All the previous statements are reasons to reinforce attention on game meat preparation and adopt effective measures and precautions to protect human health.