Abstract
The role of pigs in the maintenance of bovine tuberculosis caused by Mycobacterium bovis has been demonstrated in many settings; however, the current control programs usually do not state any intra-vitam diagnostic procedure in this species, as for the cattle. Carcass inspection has shown to be insufficient to detect infection in swine; thus, the assessment of intradermal tuberculin test and interferon-gamma release assay (IGRA) in this species is mandatory. The current study compares the performances of the single intradermal comparative cervical tuberculin (SICCT) test and IGRA. A total of 628 Nebrodi Black pigs raised in free-roaming farms were subjected to the two tests simultaneously. Besides, 124 animals underwent postmortem examination for the detection of tuberculous lesions and isolation of mycobacteria from target organs. The two tests showed a concordance of 94.42% with a Cohen's k coefficient of 0.786 and McNemar chi-square of 4.83 (P = 0.03). Slightly lower levels of concordance (90.32%) between SICCT and IGRA were obtained in the group of 124 animals, with a Cohen's k = 0.797 and McNemar chi-squared value of 0.69 with a non-significant P = 0.41. Moreover, the results showed how IGRA tends to result positive in higher rates, mostly when non-tuberculous mycobacteria (NTM) were isolated, suggesting a possible impairment of specificity in the event of coinfections in the swine. In conclusion, the results obtained support the possibility of the strategic use of IGRA or SICCT in combination or alternatively one to the other, particularly IGRA which showed lower specificity but has evident advantages over SICCT.
Highlights
Despite being named after its main host, bovine tuberculosis is a chronic, weakening infectious disease caused by Mycobacterium bovis which infects a broad host spectrum [1]
Intra-vitam Tuberculosis Tests in Pigs has been demonstrated to be highly susceptible to mycobacteriosis caused by M. bovis, and the detection of severe generalized lesions reported in pigs and wild boars suggests that those species may act as maintenance hosts rather than dead-end hosts in peculiar epidemiological contexts [2, 3]
When the performances of the two tests were compared, concordance accounted for 94.42%, with a McNemar chi-squared = 4.83 (P = 0.03) and k = 0.786, demonstrating how these two tests are highly comparable in the context examined
Summary
Despite being named after its main host, bovine tuberculosis (bTB) is a chronic, weakening infectious disease caused by Mycobacterium bovis which infects a broad host spectrum [1]. The role of wildlife seems to be crucial for the disease persistence [6] as it is well-established that sharing pastures and water sources between infected and uninfected animals makes the interspecies transmission very likely [7] In this scenario the application of systematic intra-vitam testing restricted to cattle and neglecting the role of the other susceptible species poses several obstacles to the current eradication programs in many countries. The two available intra-vitam assays are the single intradermal tuberculin (SIT) test and interferon-gamma release assay (IGRA), which measure the cell-mediated immune response (CMI), the earliest response to the infection [8] These tests have been adapted from the bovine species and the scientific literature dealing with their use in suids is scarce. The primary purpose of the present study is to compare the performances of the two intra-vitam diagnostic methods (IGRA and SICCT), in support of future decisions concerning bTB control programs in pigs
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