Resolution of Mycobacterium bovis infection in wild brushtail possums (Trichosurus vulpecula)

The brushtail possum (Trichosurus vulpecula) is the principal wildlife reservoir of Mycobacterium bovis in New Zealand (Morris and Pfeiffer 1995). Tuberculosis in possums is a progressive, fatal infection. The complete resolution of infection in possums has not been reported. The purpose of this communication is to present two cases of complete and spontaneous resolution of tuberculosis in wild, naturally infected possums. During an 11-year (1989-2000) longitudinal study of a possum population at Castlepoint in the Wairarapa, 90 bacteriologically-confirmed cases of M. bovis infection were observed, and 88 of the tuberculous possums were either found dead or were presumed to have died when they ceased to be trapped. As the home range of adult possums is stable (Efford et al 2000) it was assumed that if an adult possum could no longer be trapped, it had died. In many cases, the declining physical condition of a tuberculous possum prior to its disappearance supported the assumption. However, two cases survived and were euthanised, one 15 months and the other 30 months after they first showed clinical signs of infection. When examined post mortem, neither showed evidence of M. bovis infection. The case histories are described and the significance of the observations discussed.     

Natural transmission of Mycobacterium bovis infection in captive brushtail possums (Trichosurus vulpecula)

AIMS: To examine natural transmission of bovine tuberculosis (Mycobacterium bovis infection) in captive brushtail possums (Trichosurus vulpecula) and to determine if this mode of transmission could be employed to challenge possums in vaccination studies. METHODS: Three experiments were conducted. In Experiment 1, 11 pairs of possums were housed together in cages, one of the pair having been experimentally infected with M. bovis. Of the in-contact possums 5/11 had been vaccinated with bacille Calmette-Guerin (BCG). In Experiment 2, three susceptible possums were placed in a colony of 19 possums that had been experimentally infected with M. bovis. In Experiment 3, the four most socially active possums in each of two colonies (24 possums in one colony and 23 in the other) were experimentally infected with M. bovis, and 10 of the remaining possums in each colony were vaccinated with BCG. RESULTS: In Experiment 1, transmission of M. bovis infection occurred in only 1/11 pairs. In Experiment 2, none of the three in-contact possums became infected. In Experiment 3, infection was transmitted to 5/20 in-contact possums in one colony and 12/19 in-contact possums in the other. The possums that became infected by natural transmission were significantly more socially interactive than those that remained free of infection (p<0.05). CONCLUSIONS: When susceptible and infected possums were randomly mixed, the rate of transmission of M. bovis was low, but when highly sociable possums were infected the rate of transmission increased markedly. The risk of transmission was dependent on the close proximity of infected and susceptible possums and the frequency and duration of their social interactions. Natural transmission from experimentally infected to incontact possums in a colony would be a useful way of studying the pathogenesis of tuberculosis in this species, and the social behaviour of the possums studied should be taken into account. The high degree of variation in the rate of natural transmission of M. bovis infection between possums makes this mode of transmission unreliable for assessing vaccine efficacy.     

Isolation of Mycobacterium bovis from brushtail possums with non-visible lesions

AIM: To determine the prevalence of Mycobacterium bovis infection in brushtail possums (Trichosurus vulpecula) that did not have macroscopic lesions of bovine tuberculosis, and to evaluate culture of pooled tissues from multiple possums as a method for determining the M. bovis-infection status of wildlife populations in New Zealand.

METHODS: Pools of selected tissues were collected from possums from four different populations known to be infected with M. bovis. Tissue pools from individual animals, and combined pools from multiple animals, were cultured for M. bovis.

RESULTS: In the four populations investigated, the prevalence of possums with macroscopic lesions confirmed by culture to be infected with M. bovis ranged from 1 to 19 (mean 31/283; 10.9)%. The prevalence of possums with non-visible lesions that were culture positive for M. bovis in the same populations ranged from 4 to 10 (mean 24/283; 8.5)%. The mean of the log10 cfu of M. bovis of the macroscopic lesions and of the culture-positive samples that did not have visible lesions was 3.85 (SE 0.26) and 1.46 (SE 0.26) log₁₀ cfu, respectively (p<0.01). Mycobacterium bovis was cultured from pools of 30–50 animals in the four populations studied.

CONCLUSIONS: The finding of M. bovis infection in possums with non-visible lesions identified a potential deficiency of declaring possum populations free of M. bovis on the basis of absence of macroscopic lesions. The culturing of pools of selected tissues from multiple animals without visible lesions can be used to reduce laboratory costs of possum surveys without a major reduction in the ability to detect M. bovis infection.     

The pathogenesis of experimental endo-bronchial Mycobacterium bovis infection in brushtail possums (Trichosurus vulpecula)

AIM: To study the nature and development of experimentally induced respiratory tuberculosis in possums and compare the lesions observed with those seen in the natural disease. METHODS: Thirty-three adult possums were inoculated via the endo-bronchial route with 20-100 colony forming units of Mycobacterium bovis. The possums were killed at 1,2,3 and 4 weeks after inoculation and the nature and distribution of the lesions studied in detail histopathologically. Alveolar macrophages recovered from the infected possums were also studied ultrastructurally. RESULTS: Macroscopic lesions were largely confined to the respiratory tract, increasing in size and number with time. Histology greatly increased the detection of the total number of lesions. The most common sites affected outside the respiratory tract were the liver and hepatic lymph nodes, but lesions were less common in peripheral lymph nodes than is observed in the natural disease. Intra-pulmonary lesions were centred on blood vessels and their associated lymphatics. Peripheral blood lymphocyte blastogenic responses to M. bovis antigens were first detected at 3 weeks after inoculation, which was 1 week after lymphocyte infiltrations were detected in the lungs, but 1 week before the majority of infections became generalised. CONCLUSIONS: Differences in the nature of pulmonary lesions and the distribution of lesions were observed between experimentally induced and the natural disease. Rapid haematogenous and lymphatic spread occurs early in the experimentally induced disease.     

The pathogenesis of experimental endo-bronchial Mycobacterium bovis infection in brushtail possums (Trichosurus vulpecula)

Aim. To study the nature and development of experimentally induced respiratory tuberculosis in possums and compare the lesions observed with those seen in the natural disease.

Methods. Thirty-three adult possums were inoculated via the endo-bronchial route with 20–100 colony forming units of Mycobacterium bovis. The possums were killed at 1, 2, 3 and 4 weeks after inoculation and the nature and distribution of the lesions studied in detail histopatbologically. Alveolar macrophages recovered from the infected possums were also studied ultrastructurally.

Results. Macroscopic lesions were largely confined to the respiratory tract, increasing in size and number with time. Histology greatly increased the detection of the total number of lesions. The most common sites affected outside the respiratory tract were the liver and hepatic lymph nodes, but lesions were less common in peripheral lymph nodes than is observed in the natural disease. Intra-pulmonary lesions were centred on blood vessels and their associated lymphatics. Peripheral blood lymphocyte blastogenic responses to M. bovis antigens were first detected at 3 weeks after inoculation, which was 1 week after lymphocyte infiltrations were detected in the lungs, but 1 week before the majority of infections became generalised.

Conclusions. Differences in the nature of pulmonary lesions and the distribution of lesions were observed between experimentally induced and the natural disease. Rapid haematogenous and lymphatic spread occurs early in the experimentally induced disease.     

Experimental infection of brushtail possums (Trichosurus vulpecula) with Mycobacterium bovis by conjunctival instillation

In New Zealand, the brushtail possum (Trichosurus vulpecula) is the major wildlife reservoir of Mycobacterium bovis. Procedures for experimentally infecting possums are required to study the pathogenesis of the disease and to challenge possums in vaccine efficacy studies. Conjunctival instillation of a suspension of M. bovis was effective in producing bovine tuberculosis in captive possums. The experimental disease progressed slowly with the development of palpable lesions in superficial lymph node lesions, both characteristics of the disease in wild, naturally infected possums. At necropsy there was widespread distribution of macroscopic and microscopic lesions. The proportion of possums that became diseased, the rate of development and severity of lesions, the severity of clinical signs, all increased when the dose of M. bovis was increased. Of the three doses used, the medium dose (1000-2000 colony forming units) produced the disease with the most desired characteristics. As a procedure for exposing possums to infection with M. bovis the conjunctival route has advantages in that it is simple and safe to perform, and possums need only to be sedated for infection.     

Mortality rate and movements of brushtail possums with clinical tuberculosis (Mycobacterium bovis) infection

AIM: To describe the mortality rate and movements of brushtail possums (Trichosurus vulpecula) with clinical tuberculosis (Mycobacterium bovis) from a site in native podocarp/hardwood forest, in the Orongorongo Valley, Wellington. METHODS: Possums with clinical tuberculosis (Tb) were identified through routine trapping on live capture grids and were fitted with radio-collars, and located at approximately monthly intervals for 2.5 years. The survival times of radio-collared tuberculous and non-diseased possums were used to estimate the instantaneous additional mortality rate due to clinical Tb. The spatial behaviour of clinically tuberculous possums was compared with that of non-diseased possums, using both den and trap locations. The frequency of long-distance movements of both tuberculous and non-diseased possums was also determined. A possum was defined as having undertaken along-distance movement when it moved at least 200 m from the centre of its activity range and then returned to its established activity range or died. RESULTS: The mean survival time of clinically tuberculous possums was 4.7 (SE 0.79) months. The instantaneous additional mortality rate due to clinical Tb was estimated to be between 1.08 year-1 and 2.38 year-1, with the lower figure including an unknown portion of the incubation period in the estimate. Estimates of denning and activity ranges of tuberculous possums were approximately 22-30% larger, on average, than the ranges of non-diseased possums, but the differences were not significant. Both tuberculous and non-diseased possums undertook long-distance movements up to 700 m from the centre of their activity range. However, the majority of tuberculous possums died within or near their established activity range. CONCLUSIONS: This study estimated the mortality rate during the clinical stages of Tb and, as such, did not represent a true estimate of the disease-induced mortality rate (alpha) used in most epidemiological models of possums and Tb. However, the lower estimate of the additional mortality rate due to clinical disease could be considered an approximation to alpha. The movement patterns of clinically tuberculous possums were, overall, not substantially different from non-diseased possums. The occurrence of long-distance movements by tuberculous possums sometimes coincided with the advanced stage of clinical disease. However, the majority of tuberculous possums died within their established activity area. Long-distance movements by resident possums during the terminal stages of disease represent a direct risk for transmission of Tb to livestock on farms within approximately 1 km of infected possum populations.     

Effects of sustained control of brushtail possums on levels of Mycobacterium bovis infection in cattle and brushtail possum populations from Hohotaka, New Zealand

AIMS: To examine the effect of reducing the abundance of brushtail possums (Trichosurus vulpecula) on the distribution and prevalence of bovine tuberculosis (Mycobacterium bovis, Tb) in possums and the incidence of Tb in domestic cattle on a group of farms in the central North Island, New Zealand. METHODS: The cumulative yearly incidence of Tb infection from 12 cattle herds was estimated from annual tuberculin testing and abattoir inspection data over the period 1983-98. Intensive control of possum populations began for six of the herds in 1988, five herds in 1994 and the remaining herd in 1996. The prevalence and distribution of macroscopic M. bovis infection in possums and an index of possum abundance was estimated during yearly cross-sectional surveys from 1988 to 1998. This enabled formal testing of the link between the abundance of tuberculous possums and the incidence of Tb in cattle. RESULTS: Before possum control, infected possums were clustered in foci on or adjacent to the farms with the highest annual incidence of tuberculosis in cattle, and had an overall prevalence of macroscopic M. bovis infection of 2.3%. The prevalence of disease declined to zero with ongoing possum control, although infected possums continued to be found during the first 5 years of control. Maintaining the possum population at an average of 22.1% of its pre-control density significantly reduced the odds of the cumulative yearly incidence of Tb in cattle by 77% during the first 5 years of possum control and a further 65% in the second 5-year period. Nine of 11 tuberculous possums identified since the start of possum control were found within the areas where infected possums were clustered during the pre-control survey, suggesting that the persistence of infection within these clusters rather than infected immigrants was the source of ongoing disease. Annual estimates of the prevalence of tuberculous possums broadly followed the predictions of Barlow's possum-Tb model for a controlled possum population. CONCLUSION: The results support the hypothesis that tuberculous possums transmit bovine tuberculosis to domestic cattle, and therefore that reducing the abundance of tuberculous possums reduces the incidence of Tb in cattle. If the level of possum culling is sufficient, it appears that M. bovis infection may be eradicated from possum populations. Better information on population density, rate of increase and annual culling rates would have been needed for a truly independent examination of the Barlow possum-Tb model.     

The epidemiology of Mycobacterium bovis infection in brushtail possums (Trichosurus vulpecula Kerr) in the Hauhungaroa Ranges, New Zealand

The prevalence of Mycobacterium bovis infection in the wild possum population around the perimeter of the Hauhungaroa Ranges, New Zealand, was determined by a cross-sectional study, and risk factors associated with tuberculosis were identified. Of 6083 possums necropsied, 128 (2.1%) showed gross lesions suggestive of tuberculosis infection, and 76 (1.25%) were subsequently confirmed as tuberculous on histopathological examination. Considering only traplines where tuberculosis was detected, adult possums were 1.9 times as likely to be infected as immature animals, and the total prevalence was 5.4% in males compared with 3.9% in females. Adult females were 3.64 times as likely to be infected as immature females, whereas there was no significant age difference for males (odds ratio = 1.46, p=O.29). Immature males were 3.12 times as likely to be infected as immature females. Possums in poor condition were more likely to be found infected than possums in good condition. Tuberculous possums were found in 27 local clusters of infection. The correlation between the prevalence of tuberculosis in possums in zones and the incidence of tuberculosis in cattle on adjoining properties was 0.4 (p相似文献   

Habitat-related prevalence of macroscopic Mycobacterium bovis infection in brushtail possums (Trichosurus vulpecula), Hohonu Range, Westland, New Zealand

AIM: To identify broadscale habitat factors influencing the prevalence of macroscopic Mycobacterium bovis infection in brushtail possums (Trichosurus vulpecula) at a site in Westland, New Zealand. METHODS: During 1973/74, 1989/90 and 1997, we undertook repeated cross-sectional surveys of M. bovis infection in a possum population on the Hohonu Range , Westland. Data were analysed to determine the influence of site-specific habitat characteristics (land form, aspect, slope, altitude), distance from forest-pasture margin and time since infection on the spatial and temporal prevalence of macroscopic M. bovis infection. RESULTS: The prevalence of M. bovis infection was highest in 1973/74 (13.4%), compared with 1989/90 (3.1%) and 1997 (9.4%). The prevalence of macroscopic M. bovis infection was significantly influenced by habitat, as indexed by altitude and slope in this study site. Every 100 m increase in elevation was associated with a 29% decrease in the odds of infection, and every 10 degrees increase in slope was associated with a 20% decrease in the odds of infection. For possums caught in the lowland podocarp forest (altitude 100-200 m, average slope=5.7 degrees ), the odds of infection were nearly 30-fold higher than those for possums caught in high-altitude hardwood forest near the tree line (altitude 900-1000 m, average slope=28 degrees ). Whilst the prevalence of disease fluctuated markedly between surveys, its broadscale spatial distribution changed little over time. Proximity to the forest-pasture margin had no significant influence on the prevalence of disease, once the effect of habitat was taken into account. CONCLUSION: The prevalence of macroscopic M. bovis infection in possums was strongly influenced by habitat type, being highest in habitats that supported the highest density of possums, and lowest in habitats where population density was low. There was no evidence of progressive spread of M. bovis infection in possums into forest away from pasture-forest margins over the 24-year period of these surveys.     

Naturally occurring tuberculosis caused by Mycobacterium bovis in brushtail possums (Trichosurus vulpecula): III. Routes of infection and excretion

Mycobacterium bovis was cultured from nine of 25 (36%) tracheal washings but not from any of 38 urine and 38 faecal samples from tuberculous possums cross-sectionally sampled from the wild. One of three tracheal washings, one of three urine samples and one of three faecal samples from terminally ill possums were culture-positive. The respiratory route is implicated as the major route of excretion of Mycobacterium bovis from naturally infected possums in horizontal transmission. Tuberculosis was observed in two young possums and was evidence of probable pseudo-vertical transmission via the respiratory route or ingestion of milk. Discharging fistulae were present in 22 of 71 (31%) cross-sectionally sampled tuberculous possums and were associated with relatively advanced disease. Although the frequent involvement of superficial lymphocentres in early stage disease could not be explained satisfactorily, the respiratory route was implicated as the main route of infection from indirect evidence.     

Naturally occurring tuberculosis caused by Mycobacterium bovis in brushtail possums (Trichosurus vulpecula): II. Pathology

The gross and microscopic lesions due to Mycobacterium bovis infection are described in 73 brushtail possums (Trichosurus vulpeculu) from population studies and from 11 terminally ill possums. Subcutaneous lesions were suppurative in nature, often discharging through sinuses to the exterior. Histologically, the smallest lesions comprised focal aggregations of macrophages with angulated cytoplasmic boundaries occasionally containing acid-fast organisms. Larger lesions were pyogranulomatous, with extensive necrosis, caseation and large numbers of intra- and extra-cellular acid-fast organisms. Few multinucleate giant cells were seen and fibroplasia was rare. Mineralisation was recorded in tuberculous lymph nodes from only two possums. Histological evidence of haematogenous and lymphatic spread was seen in some cases.     

Ranging behaviour and duration of survival of wild brushtail possums (Trichosurus vulpecula) infected with Mycobacterium bovis

AIM: To quantify the duration of survival of possums (Trichosurus vulpecula) infected with Mycobacterium bovis, and identify aspects of their behaviour which may influence the likelihood of disease transmission to domestic stock or wildlife. METHODS: Capture and den locations of 14 naturally infected tuberculous possums, eight possums experimentally infected with M. bovis and eight non-infected possums were recorded between May 1998 and February 2000 at a study site near Castlepoint on the Wairarapa coast of the North Island in New Zealand. Denning behaviour was observed weekly using radiotelemetry, and possums were captured, examined and released bi-monthly. Data were used to estimate survival period; create denning, activity, and total ranges; and to identify extended forays by possums as individuals and groups. RESULTS: Seventeen tuberculous possum carcasses were recovered, of which 14 (82%) were close to or within their activity range. Denning ranges were known for 10/17 possums that died. Four tuberculous possums were found dead within their denning range. Three possums made extended forays in the 3 weeks before death. Twelve possums were found dead in dense scrub, three in long grass in open woodland and two on pasture. Mean duration of survival of naturally infected possums following detection of clinical signs was 3.4 months (95% CI=2.1-5.4) and the instantaneous mortality rate was 0.293 per month (95% CI=0.184-0.470). Signs of disease were obvious for about 3 weeks prior to death. Tuberculous possums were commonly trapped on only part of the area where the total non-infected population was trapped. CONCLUSION: Most tuberculous possums died within their activity range and in scrub, representing a risk of transmission of M. bovis to wildlife and livestock that forage in scrub. Smaller proportions dying on pasture represent a less frequent, but highly visible risk. Tuberculous possums were clustered on the study site, and localised possum control operations would be more effective if focussed on such areas.     

Longevity of Mycobacterium bovis in brushtail possum (Trichosurus vulpecula) carcasses,and contact rates between possums and carcasses

Abstract

AIM: To determine, for a variety of environmental conditions, how long Mycobacterium bovis might remain viable inside the carcass of a brushtail possum (Trichosurus vulpecula) that died of bovine tuberculosis (Tb), and to measure the rate of contact between free-ranging possums and possum carcasses.

METHODS: Lesions of M. bovis were simulated by inoculating excised spleens weighing 0.5–1 g with 0.2 mL liquid culture containing approximately 5 x 10⁷ cfu M. bovis/mL. Simulated lesions were inserted into possum carcasses (n=48) at the peripheral lymph nodes. Carcasses were placed in the field at two sites (a tussock grassland and a podocarp-broadleaved forest site) and in two seasons (summer and winter) for up to 62 days. Survival rates of M. bovis were estimated by sampling the simulated lesions over time, and culturing the recovered lesion to determine if any viable M. bovis bacteria were present.

The time taken for a free-ranging possum to first encounter a dead possum in its home range was estimated by live-trapping possums and fitting them with proximity loggers (n=13). A ‘contact’ was recorded if these possums came within 40–50 cm of proximity loggers fitted to possum carcasses.

RESULTS: There were strong seasonal and site effects in the survival rate of M. bovis in possum carcasses. In the grassland habitat, no viable bacilli were cultured from any carcass after 3 days in summer, whereas in winter all samples were culture-positive for the first 20 days, and some were still positive after 27 days. The survival rates for forest habitat were intermediate between the results for grassland, and there were no culture-positive carcasses after 9 days in summer or 27 days in winter.

In summer, infected carcasses (n=6) were first encountered by possums a mean 1.9 (range 0.4–6.7) days after placement.

CONCLUSIONS: Possum carcasses were contacted by free-ranging possums within the period that viable M. bovis were shown to survive in a carcass. The risk of such infection is likely to be most significant in winter or in areas with microhabitats where the survival of M. bovis is high. However, the generally low survival rate of M. bovis in possum carcasses and the low frequency of possum-to-carcass contacts indicate this route of transmission alone could not maintain Tb in a possum population.     

Naturally occurring tuberculosis caused by Mycobacterium bovis in brushtail possums (Trichosurus vulpecula): I. An epidemiological analysis of lesion distribution

Gross and microscopic lesion distributions and culture test results are described for 73 tuberculous possums recovered from a series of cross-sectional studies involving about 500 detailed necropsies. Pathological findings from 11 terminally ill tuberculous possums are also described. Quantitative epidemiological techniques were applied to lesion site data to assess factors influencing the pathogenesis of the disease. In possums with gross lesions, the number of distinct body sites affected varied from one to 10 per animal, with a mean of 4.6. The total number of gross plus microscopic lesions varied from one to 28 per animal with a mean of 11.6, indicating that the degree of generalisation of disease was much greater than appeared grossly. Of 119 possums with no gross lesions which were subjected to additional examinations, tuberculosis was diagnosed in ten (8.4%) by histology or culture of pooled lymph nodes. Among cross-sectional sample tuberculous possums, lesions were found in lungs in 85%, in axillary lymphocentres in 85%, in inguinal lymphocentres in 69%, and in either axillary or inguinal lymphocentres in 95%, indicating that the disease spread rapidly to multiple body sites. More males than females were infected (relative risk = 1.78). When cross-sectionally sampled infected and non-infected possums were compared, no significant associations were found between the presence/absence of disease and either age or indices of body condition, although debility was seen in animals with terminal illness.     

Evaluation of three serological tests for diagnosis of Maedi-Visna virus infection using latent class analysis

Maedi-Visna virus (MVV) infection in sheep is present in several European countries, including Norway. The current Norwegian surveillance and control programme for MVV infection uses three serological tests: an agar gel immunodiffusion test (AGID) and two commercially available indirect ELISAs (Institut Pourquier, P-ELISA and HYPHEN BioMed, H-ELISA). From 18 flocks with suspected or confirmed MVV infection, sera from naturally infected sheep were obtained, and sensitivity (Se) and specificity (Sp) of the three tests were estimated in absence of a perfect reference test using latent class models in a Bayesian analysis. The AGID had higher Sp (95% posterior credibility interval (PCI) [98.4; 99.9]) than either ELISA (95% PCI: P-ELISA, [95.1; 99.0]; H-ELISA, [91.4; 96.6]), but much lower Se (95% PCI: AGID, [41.4; 59.8]; P-ELISA, [92.7; 100.0]; H-ELISA, [90.9; 99.4]). Currently the P-ELISA is used for screening and positive samples are subsequently confirmed by a setup using all three tests in a serial reading. The Se and Sp of the serial interpretations with and without the H-ELISA were estimated. The results suggested that the H-ELISA could be dropped as a confirmatory test as the Se of the three test serial reading was reduced significantly without adding a significant improvement of the Sp compared to the serial reading of the P-ELISA and AGID alone. However, the perceived cost of false positives versus false negatives will influence this decision. Estimates of the predictive values for the tests and combinations suggested that the P-ELISA is a good choice of screening, but confirmatory tests are needed to achieve acceptable levels of positive predictive values.     

Agreement between the caudal fold test and serological tests for the detection of Mycobacterium bovis infection in bison

The objective of this study was to estimate agreement between the caudal fold test (CFT) and different serological tests for the detection of Mycobacterium bovis infection in bison by using prevalence-adjusted bias-adjusted kappa (PABAK). A total of 212 of wild wood bison from Wood Buffalo National Park were tested with the CFT as well as several serological tests: fluorescent polarization assay (FPA), multiantigen print immunoassay (MAPIA), rapid lateral-flow test (RT) and dual path platform test (DPP). For RT, 3 variations were conducted using 30μl of serum (RT 30), 20μl of serum (RT 20) and 20μl of serum considering only a strong reaction as positive (RT 20 ST). The McNemar's χ(2) test was conducted to assess whether the proportion of positive test results to 2 different tests differed. Two measures of agreement between pair of tests were estimated: the Cohen's kappa statistic and PABAK. The apparent prevalence of tuberculosis in the sampled animals varied depending on the diagnostic test from 6.1% (FPA and DPP) to 47.2% (CFT). The prevalence estimated by CFT differed from the prevalence estimated by the other tests, whereas the prevalence estimated by FPA, MAPIA, RT 20 ST and DPP were not significantly different. The kappa and PABAK estimates calculated between CFT and the rest of the tests suggested poor to slight agreement between tests (k and PABAK<0.25 in all cases). The PABAK estimates for the pairwise combinations among serological tests were numerically greater than the kappa estimates (and significantly greater when FPA was compared to the rest of serological tests), and suggested substantial to almost perfect agreement (PABAK>0.75 in all cases). The disagreement between the skin and serological tests for the detection of M. bovis infection could be partly because the tests measure different immunological responses (cell-mediated vs. humoral) that are predominant at different stages of the infection, and partly due to inaccuracy of the tests. Further research is needed to evaluate the accuracy of diagnostic tests in order to establish a reliable case definition, combining different tests, to be used in the surveillance and control of tuberculosis in free-ranging bison populations.