Diagnostic Value of Animal-Side Antibody Assays for Rapid Detection of Mycobacterium bovis or Mycobacterium microti Infection in South American Camelids

Abstract

Tuberculosis (TB) in South American camelids (SAC) is caused byMycobacterium bovis or Mycobacterium microti. Two serological methods, rapid testing (RT) and the dual-path platform (DPP) assay, were evaluated using naturally infected SAC. The study population included 156 alpacas and 175 llamas in Great Britain, Switzerland, and the United States. TB due to M. bovis (n ‫؍‬ 44) or M. microti (n ‫؍‬ 8) in 35 alpacas and 17 llamas was diagnosed by gross pathology examination and culture. Control animals were from herds with no TB history. The RT and the DPP assay showed sensitivities of 71% and 74%, respectively, for alpacas, while the sensitivity for llamas was 77% for both assays. The specificity of the DPP assay (98%) was higher than that of RT (94%) for llamas; the specificities of the two assays were identical (98%) for alpacas. When the two antibody tests were combined, the parallel-testing interpretation (applied when either assay produced a positive result) enhanced the sensitivities of antibody detection to 89% for alpacas and 88% for llamas but at the cost of lower specificities (97% and 93%, respectively), whereas the serial-testing interpretation (applied when both assays produced a positive result) maximized the specificity to 100% for both SAC species, although the sensitivities were 57% for alpacas and 65% for llamas. Over 95% of the animals with evidence of TB failed to produce skin test reactions, thus confirming concerns about the validity of this method for testing SAC. The findings suggest that serological assays may offer a more accurate and practical alternative for antemortem detection of camelid TB.Tuberculosis (TB) remains one of the most challenging and widespread zoonotic diseases in many countries (5,6,34). Mycobacterium tuberculosis and Mycobacterium bovis are the primary etiologic agents for human and bovine TB, respectively (8,30,39). M. bovis in particular is also known to cause TB in a broad range of domestic and wild mammal species (24,35). Infections with M. bovis have been shown to affect both New and Old World species of camelids (14,36,44,45). Tuberculosis in South American camelids (SAC), particularly in alpacas and llamas, has recently gained particular attention in Europe and in the United States, where these animals are being increasingly traded and kept in growing numbers as an alternative livestock industry (1). In recent years, M. bovis infections have been documented in alpaca and llama herds in parts of Europe, such as Great Britain (GB) (7, 37, 38), Ireland (32), and Spain (11), where this infection is endemic in cattle and wildlife. Also, SAC are known to be susceptible to M. microti, another member of the M. tuberculosis complex that can cause generalized disease with a fatal outcome in SAC (26,29,46). These infections are usually difficult to recognize in live animals because of the lack of reliable antemortem diagnostic tests and the nonspecific nature of the clinical signs of TB (4, 12). The intradermal tuberculin test is used in many countries, but that method is...

Evaluation of Gamma Interferon and Antibody Tuberculosis Tests in Alpacas

“…Lyashchenko et al (9) compared the Stat-Pak and DPP serological tests in TB-infected llamas and alpacas across Great Britain (alpacas), Switzerland (llamas), and the United States (alpacas) and found only small differences in test sensitivity and specificity, with slightly higher sensitivity for both tests and identical (Stat-Pak) or slightly lower (DPP) specificity in llamas compared to alpacas. Our study, by necessity, was carried out using the most populous species of SAC in Great Britain (alpacas), and so we cannot at this stage know the magnitude of any species variation (if any) in Great Britain.…”

“…Camelids are susceptible to tuberculosis (TB) caused by both Mycobacterium bovis (the agent of bovine TB) and Mycobacterium microti, which was originally identified as a pathogen of small rodents and shrews but is now also known to cause tuberculosis in other species, like cats and SAC (9,14,16). The first documented case of M. bovis infection in SAC in Great Britain was reported in 1999 in llamas (2).…”

Rapid Detection of Serum Antibody by Dual-Path Platform VetTB Assay in White-Tailed Deer Infected with Mycobacterium bovis

“…The DPP format is a two-step test designed for rapid antibody detection in multiple host species (18)(19)(20), including cervids (9,11,13). The assay has two test antigen bands on the membrane strip, T1 (MPB83 protein) and T2 (CFP10/ESAT-6 fusion), for differential IgG antibody detection by colloidal gold particles coupled with hybrid protein A/G.…”

Field Application of Serodiagnostics To Identify Elephants with Tuberculosis prior to Case Confirmation by Culture

“…This assay format has been evaluated in different host species infected with M. tuberculosis complex organisms to demonstrate the promising potential for multispecies applications (2,3,4,18,28,29). The goal of the present work was to evaluate the predictive diagnostic value of three serologic methods, the ElephantTB STAT-PAK kit, MAPIA, and DPP VetTB assay, in a group of selected elephants which were identified as antibody positive when routinely tested by serology and eventually diagnosed with TB by culture.…”