Diagnosis of Tuberculosis in the Wild Boar (Sus scrofa): A Comparison of Methods Applicable to Hunter-Harvested Animals

Abstract

BackgroundTo obtain robust epidemiological information regarding tuberculosis (TB) in wildlife species, appropriate diagnostic methods need to be used. Wild boar (Sus scrofa) recently emerged as a major maintenance host for TB in some European countries. Nevertheless, no data is available to evaluate TB post-mortem diagnostic methods in hunter-harvested wild boar.Methodology/Principal FindingsSix different diagnostic methods for TB were evaluated in parallel in 167 hunter-harvested wild boar. Compared to bacteriological culture, estimates of sensitivity of histopathology was 77.8%, gross pathology 72.2%, PCR for the MPB70 gene 66.7%, detection of acid-fast bacilli (AFB) in tissue contact smears 55.6% and in histopathology slides 16.7% (estimated specificity was 96.7%, 100%, 100%, 94.4% and 100%, respectively). Combining gross pathology with stained smears in parallel increased estimated sensitivity to 94.4% (94.4% specificity). Four probable bacteriological culture false-negative animals were identified by Discriminant Function Analysis. Recalculating the parameters considering these animals as infected generated estimated values for sensitivity of bacteriology and histopathology of 81.8%, gross pathology 72.7%, PCR for the MPB70 gene 63.6%, detection of AFB in tissue contact smears 54.5% and in histopathology slides 13.6% (estimated specificity was 100% for gross pathology, PCR, bacteriology and detection of AFB in histopathology slides, 96.7% for histopathology and 94.4% for stained smears).Conclusions/SignificanceThese results show that surveys for TB in wild boar based exclusively on gross pathology considerably underestimate prevalence, while combination of tests in parallel much improves sensitivity and negative predictive values. This finding should thus be considered when planning future surveys and game meat inspection schemes. Although bacteriological culture is the reference test for TB diagnosis, it can generate false-negative results and this should be considered when interpreting data.

Wildlife Tuberculosis: A Systematic Review of the Epidemiology in Iberian Peninsula

“…As the financial resources needed to perform bacteriological culture on a large number of samples are scarcely available, most surveys use other methods (usually gross pathology) as screening tests and only perform bacteriological culture for lesion-positive animals, sometimes as pooled samples. This introduces a bias and it was shown that the sensitivity of gross pathology was 72,2% of that obtained from bacteriology in the wild boar (Santos et al, 2010). The same trend has been reported elsewhere for deer (Rohonczy et al, 1996;O'Brien et al, 2004).…”

Six recommendations for improving monitoring of diseases shared with wildlife: examples regarding mycobacterial infections in Spain

“…Serum antibodies and TB-compatible lesions are time-and cost-effective in wild boar Santos et al 2010;Boadella et al 2011). …”

“…This means defining the agent or agents: M. bovis only, or members of the M. tuberculosis complex (MTBC), or MTBC and MAP, for instance; and also defining what data will be needed, be it the antigen by culture or PCR, specific antibodies or even characteristic lesions Santos et al 2010). It is important to choose parameters for which detection tools of known effectiveness are available (Wobeser 1994).…”

Facts and dilemmas in diagnosis of tuberculosis in wildlife

“…Meat inspection is currently the only method suitable for large-scale screening in slaughtered deer, with final confirmation by culturing [64]. However, as has been shown in wild boar, this may actually not be a very sensitive method [67].…”

“…Direct microscopic smear examination is a fast, inexpensive method and can provide a presumptive diagnosis, especially when clinical signs and lesions are present. Its sensitivity has been reported to be variable depending on the wildlife species and severity of infection and ranged from 55.6% in wild boar [67] to 90% in white-tailed deer [73], while in lions there was an apparent absence of acid-fast bacilli in culture positive organs [22]. On the other hand, in combination with gross pathological examination, direct microscopic smear examination was found highly sensitive (95%) in infected wild boar and recommended as a useful tool for surveys and game meat inspection schemes [67].…”