Performance of diagnostic tests for bovine tuberculosis in North American furbearers and implications for surveillance

Abstract

Summary: Risks of bovine tuberculosis (bTB) transmission from free-ranging wildlife to livestock remain a concern in the United States, in both known endemic areas and where spillover from recently-infected livestock herds occurs. Federal agriculture officials in the United States (US) have recommended surveillance of non-cervid furbearers to determine whether free-ranging wildlife in the vicinity of cattle herd breakdowns are bTB infected, yet the efficacy of common diagnostic tests in these species is largely unknown. We calculated the sensitivity, specificity, predictive values and positive likelihood ratios for bTB infection in carcasses of sixteen species of furbearers tested via: (i) the presence of gross lesions compatible with bTB; (ii) histopathology consistent with bTB; and (iii) the presence of acid-fast bacilli (AFB) on histopathology. The gold standard comparison test was mycobacterial culture of cranial ± visceral lymph nodes pooled for each animal. Forty-two animals distributed across six species cultured bTB positive from among 1522 furbearers tested over thirteen years. The sensitivity of all three tests was poor (10%, 22% and 24% for gross lesions, AFB and histopathology, respectively), while specificities (all ≥99%) and negative predictive values (all ≥97%) were high. Positive predictive values varied widely (31-75%). Likelihood ratios for culture positivity given a positive test result showed AFB on histopathology to be the most reliable test, and gross lesions the least, though confidence intervals were wide and overlapping. While non-cervid furbearers may prove useful in North American bTB surveillance, wildlife managers should be aware of factors that may abate their utility and complicate interpretation of surveillance. © 2013 Blackwell Verlag GmbH.