Spatial distribution and risk factors of Brucellosis in Iberian wild ungulates

Abstract

Background: The role of wildlife as a brucellosis reservoir for humans and domestic livestock remains to be properly established. The aim of this work was to determine the aetiology, apparent prevalence, spatial distribution and risk factors for brucellosis transmission in several Iberian wild ungulates.

Methods: A multi-species indirect immunosorbent assay (iELISA) using Brucella S-LPS antigen was developed. In several regions having brucellosis in livestock, individual serum samples were taken between 1999 and 2009 from 2,579 wild bovids, 6,448 wild cervids and4,454 Eurasian wild boar (Sus scrofa), and tested to assess brucellosis apparent prevalence. Strains isolated from wild boar were characterized to identify the presence of markers shared with the strains isolated from domestic pigs.

Results: Mean apparent prevalence below 0.5% was identified in chamois (Rupicapra pyrenaica), Iberian wild goat (Capra pyrenaica), and red deer (Cervus elaphus). Roe deer (Capreolus capreolus), fallow deer (Dama dama), mouflon (Ovis aries) and Barbary sheep (Ammotragus lervia) tested were seronegative. Only one red deer and one Iberian wild goat resulted positive in culture, isolating B. abortus biovar 1 and B. melitensis biovar 1, respectively. Apparent prevalence in wild boar ranged from 25% to 46% in the different regions studied, with the highest figures detected in South-Central Spain. The probability of wild boar being positive in the iELISA was also affected by age, age-by-sex interaction, sampling month, and the density of outdoor domestic pigs. A total of 104 bacterial isolates were obtained from wild boar, being all identified as B. suis biovar 2. DNA polymorphisms were similar to those found in domestic pigs.

Conclusions: In conclusion, brucellosis in wild boar is widespread in the Iberian Peninsula, thus representing an important threat for domestic pigs. By contrast, wild ruminants were not identified as a significant brucellosis reservoir for livestock.

Figure 1

Example of the typical distribution of optical density (% OD) results obtained by iELISA when testing the gold standard populations (from domestic goats) and its phylogenetically related Iberian wild goat (Capra pyrenaica) counterpart. The horizontal line represents the cut off selected for assessing the apparent prevalence of brucellosis.

Figure 2

Panel A: Apparent prevalence of brucellosis in Eurasian wild boar (Sus scrofa) in Bio-regions 1 to 5. Dots are proportional to prevalence. Only data from localities with at least 10 wild boar samples are shown. Panel B: Distribution of the different haplotypes of Brucella suis strains isolated from wild boar. Points represent an infected population cluster rather than individual isolates; the dotted line represents the south-western distribution limit of the European brown hare (Lepus europaeus). Panel C: Characteristics of the B. suis biovar 2 haplotypes isolated when identified by PCR (Mpx-PCR) and further analysis of omp2a, omp2b and omp31 genes by PCR-RFLP.

Figure 3

Distribution of apparent prevalence in wild boar (Sus scrofa) through age and sex classes (Panel A), and sampling period (Panel B) at the Peninsular scale.