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Brucellosis has not been reported in domestic pigs in Belgium since 1969, but in 1994, Brucella suis biovar 2 strains were isolated from hunter-killed boar, demonstrating the circulation of the bacteria amongst wild boar (Sus scrofa) populations in Belgium. Since then, B. suis biovar 2 has been isolated from wild boar in many countries of Central and Western Europe such as France, Switzerland, Germany, Spain, and Croatia.
The aims of this study were to determine the apparent seroprevalence of brucellosis in wild boar sampled in the four main hunting regions of Belgium and to identify potential risk factors associated with seropositivity. Direct and indirect brucellosis tests were also compared to determine the most suitable combination of diagnostic tools for conducting a successful prevalence study in wildlife.
Overall, 641 out of 1168 serum samples were considered positive with the indirect enzyme-linked immunosorbent assay (iELISA), giving an apparent seroprevalence rate of 54.88% (95% CI 52.03-57.73). I
A significant difference exists between the apparent seroprevalence from 1994 (39.7% with 95% CI 31.64-47.79) and the apparent overall one found in this study (χ2 = 11.62, P < 0.001, df 1). The multivariate logistic regression model performed on iELISA results showed year of sampling and age were significantly associated with boar seropositivity. In contrast, sex was not a significant influencing factor (P = 0.12). The apparent seroprevalence was affected neither by month of sampling (P = 0.95) nor by region of sampling (P = 0.80).
Over this five-year investigation, 1168 wild boar were tested. The results show that brucellosis is endemic in wild boar in southern Belgium. Both wild suid populations and brucellosis prevalences have increased from 1994 to 2007, and this constitutes a growing risk of spillback to outdoor-farmed pig herds. For financial and practical reasons, serological tests are the first tools for use in brucellosis prevalence studies in wildlife, but they must be interpreted with caution and the ELISAs used must be expressly validated for use on wild species. Furthermore, it is strongly recommended to associate them with tools for direct diagnosis. In the present study, PCR proved more sensitive than culture under wildlife sampling conditions. Spleen and tonsils are lymphoid tissues usually sampled in multi-disease monitoring programs. They remain top-grade organs for direct diagnosis of brucellosis, with a preference for tonsils.
Fabien Grégoire, Bénédicte Mousset, David Hanrez, Charles Michaux, Karl Walravens and Annick Linden. A serological and bacteriological survey of brucellosis in wild boar (Sus scrofa) in Belgium. BMC Veterinary Research 2012, 8:80 doi:10.1186/1746-6148-8-80