Single Intradermal Comparative Cervical Tuberculin Test Research Articles

Prevalence of bovine tuberculosis and analysis of risk factors among the dairy farms in and around Guwahati metropolitan city, India

Bovine tuberculosis (bTB), a neglected zoonotic disease caused by Mycobacterium bovis is being reported worldwide. The present work was carried out from December 2020 to November 2021 to assess the prevalence and risk factors of bTB in peri-urban and urban dairy farms of Guwahati, Assam, India. A questionnaire was used to collect data on knowledge about bTB on 36 farms, and ten animals per farm were screened by single intradermal comparative cervical tuberculin test (SICCT) to determine the prevalence of bTB, giving a total of 360 animals. The demographic data of the farmers revealed that 61.1% respondents were illiterate, 66.7% had no awareness about bovine tuberculosis and 41.7% consumed unpasteurised milk and milk products. SICCT showed that 38 cattle from 18 of the farms were positive reactors for bTB, yielding an overall animal level prevalence of 10.55% (95% confidence interval (CI = 7.58–14.2%) and a 50% herd prevalence (95% CI 32.9–67.1%). Animals 5 years and above were found to be more likely to be positive for bTB (17.18%). The study highlighted the widespread prevalence of bovine tuberculosis in peri-urban and urban dairy farms of Guwahati which gives a picture also about other major cities of India. Hence, it is of utmost importance to undertake a comprehensive epidemiological study in such cities for effective control and prevention of bTB in a one health approach.

Mycobacterium tuberculosis complex detection in rural goat herds in South Africa using Bayesian latent class analysis

Animal tuberculosis affects a wide range of domestic and wild animal species, including goats (Capra hircus). In South Africa, Mycobacterium tuberculosis complex (MTBC) testing and surveillance in domestic goats is not widely applied, potentially leading to under recognition of goats as a potential source of M. bovis spread to cattle as well as humans and wildlife. The aim of this study was to estimate diagnostic test performance for four assays and determine whether M. bovis infection was present in goats sharing communal pastures with M. bovis positive cattle in the Umkhanyakude district of Northern Zululand, KwaZulu Natal. In 2019, 137 M. bovis-exposed goats were screened for MTBC infection with four diagnostic tests: the in vivo single intradermal comparative cervical tuberculin test (SICCT), in vitro QuantiFERON®-TB Gold (QFT) bovine interferon-gamma release assay (IGRA), QFT bovine interferon gamma induced protein 10 (IP-10) release assay (IPRA), and nasal swabs tested with the Cepheid GeneXpert® MTB/RIF Ultra (GXU) assay for detection of MTBC DNA. A Bayesian latent class analysis was used to estimate MTBC prevalence and diagnostic test sensitivity and specificity. Among the 137 M. bovis-exposed goats, positive test results were identified in 15/136 (11.0%) goats by the SICCT; 4/128 (3.1%) goats by the IPRA; 2/128 (1.6%) goats by the IGRA; and 26/134 (19.4%) nasal swabs by the GXU. True prevalence was estimated by our model to be 1.1%, suggesting that goats in these communal herds are infected with MTBC at a low level. Estimated posterior means across the four evaluated assays ranged from 62.7% to 80.9% for diagnostic sensitivity and from 82.9% to 97.9% for diagnostic specificity, albeit estimates of the former (diagnostic sensitivity) were dependent on model assumptions. The application of a Bayesian latent class analysis and multiple ante-mortem test results may improve detection of MTBC, especially when prevalence is low. Our results provide a foundation for further investigation to confirm infection in communal goat herds and identify previously unrecognized sources of intra- and inter-species transmission of MTBC.

Effect of tuberculin skin testing on serological results against Mycobacterium avium ssp. paratuberculosis (MAP): Evidence of distinct effects in MAP-infected and noninfected cows.

Johne's disease and bovine tuberculosis are diseases of economic, public health, and animal welfare importance. The single intradermal cervical comparative tuberculin (SICCT) test, which is used to determine bovine tuberculosis status as part of eradication schemes in the United Kingdom and some other countries, has been reported to interfere with the results of the widely used ELISA to detect antibodies against Mycobacterium avium ssp. paratuberculosis (MAP) in milk. Better understanding of the relationship between SICCT and MAP tests can improve management and control of Johne's disease. The aim of this study was to characterize the relationship between SICCT testing and milk ELISA performance and to assess whether the immunological response to the SICCT test is different for MAP-infected cows and noninfected cows. We used repeated MAP milk ELISA test results of a cohort of 805,561 cows in the United Kingdom between 2010 and 2018 that had milk ELISA tests within 90 d of SICCT testing to identify cows likely to be infected. We then assessed, separately, for cows deemed to be MAP-infected and noninfected, the association between MAP test results and proximity to SICCT testing by means of survival analysis and generalized additive mixed models. The results were used to quantify the effect SICCT testing may have on performance of milk ELISA tests conducted soon after SICCT testing. At high prevalence levels (20%) of MAP in the infected herd, overall accuracy of the milk ELISA is not reduced when testing occurs within 14 d from SICCT testing. Milk ELISA values of cows deemed to be infected were highest when MAP testing was closer in time to SICCT testing, suggesting the SICCT test enhances antibody response for MAP in infected cows. This corresponds to higher sensitivity of the MAP milk ELISA when testing within 30 d of the SICCT test. For cows deemed to be noninfected, the effect of previous SICCT testing was delayed compared with infected cows, with MAP milk ELISA values peaking at around 15 d post-SICCT testing. For both, MAP-infected and noninfected cows, interference from SICCT test diminished 30 d after SICCT testing, suggesting post 30 d to be the most appropriate time for evaluating the milk ELISA for MAP after SICCT testing. Our results provide strong evidence that the effect of the SICCT test on serological response against MAP is different for MAP-infected versus noninfected cows and that, as a result of this distinct effect, it is possible to improve interpretation of MAP milk ELISA test results (higher accuracy) by taking into consideration time since SICCT testing.

Field evaluation of the tuberculin skin test for the detection of Mycobacterium tuberculosis complex infection in communal goats (Capra hircus) in KwaZulu-Natal, South Africa

In South Africa, animal tuberculosis (TB) control programs predominantly focus on domestic cattle and African buffaloes (Syncerus caffer) despite increasing global reports of tuberculosis in goats (Capra hircus). Left undetected, Mycobacterium tuberculosis complex (MTBC) infected goats may hinder TB eradication efforts in cattle and increase zoonotic risk to humans. Since the publication of animal TB testing guidelines in 2018, prescribing the use of the tuberculin skin test (TST) for goats in South Africa by the Department of Agriculture, Land Reform, and Rural Development (DALRRD), there have been no published reports of any field application of the prescribed test criteria in goat herds. Therefore, this study aimed to evaluate the performance of these DALRRD guidelines using the single intradermal cervical tuberculin test (SICT) and the single intradermal comparative cervical tuberculin test (SICCT). Between October and December 2020, 495 goats from communal pastures of Kwa-Zulu Natal (KZN), where M. bovis infection has been identified in cattle and where cattle and goats cohabitate, were tested using the SICT and SICCT (M. bovis-exposed group). Additionally, 277 goats from a commercial Saanen dairy herd, with no history of M. bovis, were also tested (M. bovis-unexposed group). Estimated apparent prevalence of TST positive goats was determined based on published test interpretation criteria as described by DALRRD. When proportions of test-positive goats were compared between different DALRRD criteria, the ≥ 4 mm cut-off criterion for the SICCT resulted in the lowest proportion of positive results in the presumably uninfected group (1/277 positive in the unexposed group). The apparent prevalence of TB in the exposed group was estimated at 3.0% (95% CI: 1.7–4.9%), which is similar to previous reports of M. bovis prevalence in cattle from this area (6%). The detection of a significantly greater proportion of SICCT positive goats in the M. bovis-exposed group compared to the unexposed group suggests that MTBC infection is present in this population. Further investigations should be undertaken, in conjunction with confirmatory molecular tests, mycobacterial culture, and advanced pathogen sequencing to establish whether MTBC infection in domestic goats is a true under-recognized threat to the eradication of animal TB in South Africa.

Prevalence and risk factors associated with bovine tuberculosis in local and crossbred dairy cattle in Debre Berhan milk shed, central Ethiopia

Bovine tuberculosis is a chronic and contagious disease of animals and humans with worldwide distribution. A cross-sectional study was employed to estimate the prevalence of bovine tuberculosis and its associated risk factors in dairy cattle found in the Debre Berhan milk shed. The study covered three districts found in the Debre Berhan milk shed for the duration of six months extending from July to December 2018. A single intradermal comparative cervicaltuberculin test was used as a screening test of bovine tuberculosis. Face-to-face interview using a structured questionnaire was also employed to collect data on the risk factors associated with bovine tuberculosis. A binary logistic regression statistical model was used for data analysis. The finding showed that the apparent individual animal level prevalence was 17% (106/625; 95% confidence interval [CI]: 14.2-20.2) at ≥ a 4mm cut-off value in 625 heads of dairy cattle tested. The herd prevalence was 16.7% (16/96; 95% CI: 10.1-26) at ≥ a 4mm cut-off value in 96 dairy herds tested. Multivariable logistic regression analysis at ≥ a 4mm cut-off value revealed that dairy cattle in poor body condition (Adjusted Odd ratio [AOR] = 3.7; 95% CI: 1.6-8.4; p = 0.002), large herd size (AOR = 29.5; 95% CI: 5.6-154.1; p = 0.000) and exotic breed (AOR = 3.7; 95% CI: 1.3-10.7; p = 0.018) had 4, 30 and 4 times the odds of tuberculin positivity with statistical significance, respectively compared to their counterparts. The findings in this study complement the works of other authors who conducted bovine tuberculosis studies elsewhere in Ethiopia. In conclusion, the prevalence of bovine tuberculosis in dairy cattle of Debre Berhan milk shedwas found to be moderately high both at animal and herd levels. Moreover, poor body condition, herd size, and breed were important predictors of tuberculin test positivity. A further in-depth study on the prevalence and associated risk factors using a larger sample size are recommended.

Prevalence of Bovine Tuberculosis among Cattle and Buffaloes in the Central Province of Sri Lanka

The Bovine tuberculosis (bTB) is a chronic disease condition in dairy cattle and a proven global zoonosis. This study was designed to identify the prevalence of bTB in dairy cattle and buffaloes in the Central Province (CP) of Sri Lanka. Single Intradermal Comparative Cervical Tuberculin (SICCT) test was performed in 20 farms (n=616 cattle and buffaloes) in three districts (NuwaraEliya; NE, Kandy; KN, and Matale; MT) in the CP. Out of the SICCT positive samples, randomly selected serum samples (n=33) of eight farms were subjected to the rapid antibody (Ab) test for further confirmation. Results were evaluated for different risk factors; age, sex, parity, body condition score (BCS), breed, herd origin, reproductive status, herd size, type of management, and duration of farm establishment. The prevalence of bTB among individual cattle and buffaloes was 22% with a 50% herd-level prevalence. In NE and KN, 34% and 19% of individuals showed positive reactions for SICCT, respectively, while all the individuals in MT were negative. There were significant statistical associations (P<0.05) were observed with the prevalence of bTB and BCS, breed, herd origin, and reproductive status; however, age, sex, parity, herd size, type of management, and duration of farm establishment were not statistically significant (P>0.05) with the prevalence of bTB.The conclusion is that, based on the SICCT test, the estimated prevalence of bTB in cattle and buffaloes in the central province of Sri Lanka is relatively high (>20%). The SICCT test could be recommended for the screening of the bTB in cattle and buffaloes in all regions of Sri Lanka to assess the island-wide prevalence of bTB, as this disease carries the risk of transmitting to humans and other susceptible animal species.

Pathology of Bovine Tuberculosis in Three Breeds of Dairy Cattle and Spoligotyping of the Causative Mycobacteria in Ethiopia.

Different breeds of cattle were observed to have a variable degree of susceptibility to bovine tuberculosis (bTB). The screening of bTB was conducted on 720 dairy cattle consisting of three breeds using the single intradermal cervical comparative tuberculin (SICCT) test. Besides this, 43 SICCT test-positive cattle were used to compare the severity of the pathology of bTB among the three breeds and to identify the causative mycobacteria using spoligotyping. The overall SICCT test positivity was 17.92% (129/720) by pooling all animals in the three farms. There was a significant difference in SICCT test positivity among the three breeds (χ2 = 71.06; p < 0.001); the highest (25.34%) was recorded in the crossbreed followed by the Boran breed (10.08%), while the least (3.14%) was recorded in the Jersey breed. On other hand, the highest median pathology score (10.0, interquartile range, IQR = 6.0–17.0) was recorded in Boran followed by cross (5.0, IQR = 3.5–7.5), while the least (3.0, IQR = 2.25–3.0) was recorded in Jersey. Thus, the difference in the median pathology scores was significant [Kruskal Wallis = 18.78, p < 0.001] among the three breeds. Furthermore, multivariate analysis using ordinal logistic regression by considering age, sex, breed, reproductive status, and location of the farms also showed a significant [ = 11.97, p < 0.01] difference in pathology scores among the three breeds of cattle. Even at a single-herd level at Holeta, the difference in severity of pathology between the Boran and crossbreeds was significant (U = 33.5; p < 0.01). Culture positivity was 39% in 108 suspicious tissues. Fourteen Mycobacterium bovis (M. bovis) and two Mycobacterium tuberculosis (M. tuberculosis) were isolated from the lesions. All the 14 M. bovis isolates belonged to SB0912, while the two M. tuberculosis belonged to SIT54. In conclusion, although the frequency of the SICCT test positivity was high in the crossbreed, a more severe pathology was observed on the Boran (zebu) breed. In addition M. tuberculosis was isolated from TB lesions of dairy cattle, demonstrating the role of M. tuberculosis in causing TB in cattle.

Field evaluation of specific mycobacterial protein-based skin test for the differentiation of Mycobacterium bovis-infected and Bacillus Calmette Guerin-vaccinated crossbred cattle in Ethiopia.

Bovine tuberculosis (bTB) challenges intensive dairy production in Ethiopia and implementation of the test and slaughter control strategy is not economically acceptable in the country. Vaccination of cattle with Bacillus Calmette–Guerin (BCG) could be an important adjunct to control, which would require a diagnostic test to differentiate Mycobacterium bovis (M. bovis)‐infected and BCG‐vaccinated animals (DIVA role). This study describes an evaluation of a DIVA skin test (DST) that is based on a cocktail (DSTc) or fusion (DSTf) of specific (ESAT‐6, CFP‐10 and Rv3615c) M. bovis proteins in Zebu–Holstein–Friesians crossbred cattle in Ethiopia. The study animals used were 74 calves (35 BCG vaccinated and 39 unvaccinated) aged less than 3 weeks at the start of experiment and 68 naturally infected ‘TB reactor’ cows. Six weeks after vaccination, the 74 calves were tested with the DSTc and the single intradermal cervical comparative tuberculin (SICCT) test. The TB reactor cows were tested with the DSTc and the SICCT test. Reactions to the DSTc were not observed in BCG‐vaccinated and unvaccinated calves, while SICCT test reactions were detected in vaccinated calves. DSTc reactions were detected in 95.6% of the TB reactor cows and single intradermal tuberculin positive reactions were found in 98.2% (95% confidence interval, CI, 92.1–100%). The sensitivity of the DSTc was 95.6% (95% CI, 87.6–99.1%), and significantly (p < .001) higher than the sensitivity (75%, 95% CI, 63.0–84.7%) of the SICCT test at 4 mm cut‐off. DSTf and DSTc reactions were correlated (r = 0.75; 95% CI = 0.53–0.88). In conclusion, the DSTc could differentiate M. bovis‐infected from BCG‐vaccinated cattle in Ethiopia. DST had higher sensitivity than the SICCT test. Hence, the DSTc could be used as a diagnostic tool for bTB if BCG vaccination is implemented for the control of bTB in Ethiopia and other countries.

Evaluation of the Efficacy of BCG in Protecting Against Contact Challenge With Bovine Tuberculosis in Holstein-Friesian and Zebu Crossbred Calves in Ethiopia.

Bovine tuberculosis (bTB) is prevalent in intensive dairy farms in Ethiopia. Vaccination could be an alternative control approach given the socio-economic challenges of a test-and-slaughter control strategy. The efficacy of the BCG was evaluated on 40 Holstein-Friesian (HF) and zebu crossbred calves recruited from single intradermal cervical comparative tuberculin (SICCT) test negative herds and randomly allocated into two groups. Twenty-two calves were vaccinated within 2 weeks of age, and 18 were kept as a control. Six weeks post-vaccination, the two groups were exposed and kept mixed with known SICCT test positive cows for 1 year. Immune responses were monitored by interferon gamma (IFN-γ) release assay (IGRA), SICCT test, and antibody assay. Vaccinated calves developed strong responses to the SICCT test at the sixth week post-vaccination, but did not respond to ESAT-6/CFP-10 peptide antigen-based IGRA. During the exposure, IFN-γ response to the specific peptide cocktail [F(2.44, 92.67) = 26.96; p < 0.001] and skin reaction to the specific proteins cocktail [F(1.7, 64.3); p < 0.001] increased progressively in both groups while their antibody responses were low. The prevalence of bTB was 88.9% (95% CI: 65.3–98.6) and 63.6% (95% CI: 40.7–83.8) in the control and vaccinated calves, respectively, based on Mycobacterium bovis isolation, giving a direct protective efficacy estimate of 28.4% (95% CI: −2.7 to 50.1). The proportion of vaccinated calves with lesion was 7.0% (34/484) against 11.4% (45/396) in control calves, representing a 38% (95% CI: 5.8–59.4) reduction of lesion prevalence. Besides, the severity of pathology was significantly lower (Mann–Whitney U-test, p < 0.05) in vaccinated (median score = 2.0, IQR = 0–4.75) than in control (median score = 5, IQR = 3.0–6.25) calves. Moreover, survival from M. bovis infection in vaccinated calves was significantly (log-rank test: χ2 = 6.749, p < 0.01) higher than that of the control calves. In conclusion, the efficacy of BCG was low, but the reduced frequency and severity of lesion in vaccinated calves could suggest its potential role in containing onward transmission.

Dynamics and risk of transmission of bovine tuberculosis in the emerging dairy regions of Ethiopia.

The Ethiopian government has several initiatives to expand and intensify the dairy industry; however, the risk of bovine tuberculosis (bTB) spread is a challenge. To assess the rate of expansion and risk factors for transmission of bTB within-herds, we carried out a repeated cross-sectional survey at two time points, 2016/17 and 2018, in three regional cities, namely, Gondar, Hawassa and Mekelle, representing the emerging dairy belts of Ethiopia. The total number of herds involved was 128, comprising an average of 2303 cattle in each round. The Single Intradermal Comparative Cervical Tuberculin (SICCT) test was used to identify reactor status and data on herd-level risk factors were collected using a structured questionnaire. In the first survey, the apparent prevalence of bTB, as measured by the SICCT test, was 4.5% (95% CI 3.7-5.4%) at the individual animal-level and 24% (95% CI 17.5-32%) at the herd-level. There was no statistically significant change in the overall apparent prevalence or regional distribution at the second survey, consistent with the infection being endemic. The incidence rate was estimated at 3.6 (95% CI 2.8-4.5) and 6.6 (95% CI 3.0-12.6) cases/100 cattle (or herd)-years at the animal- and herd-levels, respectively. Risk factors significantly associated with the within-herd transmission of bTB were age group and within-herd apparent prevalence at the start of the observation period. We noted that farmers voluntarily took steps to remove reactor cattle from their herds as a consequence of the information shared after the first survey. Removal of reactors between surveys was associated with a reduced risk of transmission within these herds. However, with no regulatory barriers to the sale of reactor animals, such actions could potentially lead to further spread between herds. We therefore advocate the importance of setting up regulations and then establishing a systematic bTB surveillance programme to monitor the impact prior to implementing any control measures in Ethiopia.

Sero-diagnosis of Bovine tuberculosis using a rapid lateral flow test and ELISA in dairy cattle in Egypt

Mycobacterium bovis (M. bovis), the cause of bovine tuberculosis (BTB) in cattle, remains a major zoonotic and economic problem in many countries. This study aimed to apply different serological tests for detection of bovine tuberculosis as a complementary for intradermal tuberculin test. The tested 4250 cattle in different Egyptian governorates by single intradermal cervical comparative tuberculin test (SICCT), 90 (2.1%) cattle reacted positively. The postmortem (PM) examination of the positive reactors revealed 65 (72.2%) out of 90 slaughtered cattle with visible lesions (VL) while the other 25 (27.8%) reactors showed no visible lesions (NVL). The visible lesions detected in head were 10 (15.4%) out of the 65 VL, in respiratory system were 32 (49.2%), in the digestive system were 5 (7.7%), in mixed infection were 11 (16.9%), and in generalized infection were 7(10.8%). The bacteriological examination of processed samples from the 90 slaughtered cattle revealed 55 M. bovis (61.1%); 51 (78.5%) were from 65 VL and 4 (16.0%) were from 25 NVL. Enzyme linked immune sorbent assay (ELISA) was used for the tuberculin positive animals’ sera and gave 36 (55.4%) out of 65 cattle with and 2 (8%) out of 25 cattle with NVL by a total 38 (42.2%) out of the 90 tuberculin positive animals. The results of lateral flow test gave 32 (49.2%) out of 65 cattle with VL and 1 (4%) out of 25 cattle with NVL by a total 33 (36.7%) out of the 90 tuberculin positive animals.

The rapid detection and differentiation of Mycobacterium tuberculosis complex members from cattle and water buffaloes in the delta area of Egypt, using a combination of real-time and conventional PCR.

Mycobacterium tuberculosis complex (MTBC) has the potential to cause infections in animals and human beings. The combination of real-time PCR targeting atpE or lpqT and RD1, and conventional PCR targeting regions of difference (RD) was rigorously evaluated as a descriptive molecular epidemiology tool. A total of 2100 cattle and buffaloes from the Menoufia, Sharkia, Gharbia, Dakahlia, Elbuhaira, and Cairo Governorates were tested by single intradermal comparative cervical tuberculin test (SICCT). The frequency was 74/2100 (3.5%); thereafter, on post-mortem examination (PM), 49/74 (66.21%) showed visible lesions, while only 25/74 (33.78%) were non-visible with a significant difference of (p < .0001). Real-time PCR using atpE or lpqT and RD1 similarly detected the frequency of infection, sensitivity, specificity, positive predictive value, negative predictive value, and accuracy, which represented 73/74 (98.65%), 98.65, 100, 100, 90.91, and 98.81%, respectively. Multiplex conventional PCR targeting RD1, 4, 9, and 12 confirmed that 49/74 (66.21%) were M.bovis, while the simplex conventional PCR targeting RD4 and RD9 confirmed mycobacteria in 71/74 (95.94%) samples, which included 61/74 (82.4%) M.bovis and 2/74 (2.7%) M.tuberculosis. Additionally, 8/74 (10.8%) exhibited mixed patterns of M.bovis and M.tuberculosis, and 3/74 (4.05%) were negative. There was a significant difference between the results of simplex and multiplex conventional PCR (p < .0001). Moreover, simplex conventional PCR targeting RD4 and RD9 proved higher sensitivity, specificity, positive predictive value, negative predictive value, and accuracy, which were 95.95, 100, 100, 76.92, and 96.43%, respectively, when compared with the values of multiplex conventional PCR targeting RD1,4,9, and 12 which were 66.22, 100, 100, 28.57, and 70.24%, respectively. The repeatability results of real-time PCR using atpE or lpqT and RD1, and simplex conventional PCR targeting RD4 and RD9 were acceptable. In conclusion, a combination of real-time PCR using atpE or lpqT and RD1 as the first step with simplex conventional PCR targeting RD4 and RD9 as the second step was reliable as a diagnostic tool.

Test characteristics of the tuberculin skin test and post-mortem examination for bovine tuberculosis diagnosis in cattle in Northern Ireland estimated by Bayesian latent class analysis with adjustments for covariates.

The single intradermal comparative cervical tuberculin (SICCT) test and post-mortem examination are the main diagnostic tools for bovine tuberculosis (bTB) in cattle in the British Isles. Latent class modelling is often used to estimate the bTB test characteristics due to the absence of a gold standard. However, the reported sensitivity of especially the SICCT test has shown a lot of variation. We applied both the Hui-Walter latent class model under the Bayesian framework and the Bayesian model specified at the animal level, including various risk factors as predictors, to estimate the SICCT test and post-mortem test characteristics. Data were collected from all cattle slaughtered in abattoirs in Northern Ireland in 2015. Both models showed comparable posterior median estimation for the sensitivity of the SICCT test (88.61% and 90.56%, respectively) using standard interpretation and for post-mortem examination (53.65% and 53.79%, respectively). Both models showed almost identical posterior median estimates for the specificity (99.99% vs. 99.80% for SICCT test at standard interpretation and 99.66% vs. 99.86% for post-mortem examination). The animal-level model showed slightly narrower posterior 95% credible intervals. Notably, this study was carried out in slaughtered cattle which may not be representative for the general cattle population.

Bayesian latent class estimation of sensitivity and specificity parameters of diagnostic tests for bovine tuberculosis in chronically infected herds in Northern Ireland

In the European Union, the recommended ante-mortem diagnostic methods for bovine tuberculosis (bTB) include the single intradermal cervical comparative tuberculin (SICCT) test and the interferon-gamma (IFN-γ) test as an ancillary test. The SICCT test has a moderate sensitivity (Se) and high specificity (Sp), while the IFN-γ test has good Se, but a lower Sp than the SICCT test. A retrospective Bayesian latent class analysis was conducted on 71,185 cattle from 806 herds chronically infected with bTB distributed across Northern Ireland (NI) to estimate the Se and Sp of the common ante-mortem tests and meat inspection. Analyses were also performed on data stratified by farming type and herd location to explore possible differences in test performance given the heterogeneity in the population. The mean estimates in chronically infected herds were: (1) ‘standard’ SICCT: Se 40.5–57.7%, Sp 96.3–99.7%; (2) ‘severe’ SICCT: Se 49.0%–60.6%, Sp 94.4–99.4%; (3) IFN-γ(bovine–avian) using a NI optical density (OD) cut-off difference of 0.05: IFN-γ(B–A)NI: Se 85.8–93.0%, Sp 75.6–96.2%; (4) IFN-γ(bovine–avian) using a standard ‘commercial’ OD cut-off difference of 0.1: IFN-γ(B–A)0.1: Se 83.1–92.1%, Sp 83.1–97.3%; and (5) meat inspection: Se 49.0–57.1% Se, Sp 99.1–100%. Se estimates were lower in cattle from dairy farms than from beef farms. There were no notable differences in estimates by location of herds. Certain population characteristics, such as production type, might influence the ability of bTB tests to disclose truly infected cases.

Bovine tuberculosis visible lesions in cattle culled during herd breakdowns: the effects of individual characteristics, trade movement and co-infection

BackgroundBovine tuberculosis (bTB), caused by Mycobacterium bovis, remains a significant problem for livestock industries in many countries worldwide including Northern Ireland, where a test and slaughter regime has utilised the Single Intradermal Comparative Cervical Tuberculin (SICCT) test since 1959.We investigated the variation in post-mortem confirmation based on bTB visible lesion (VL) presence during herd breakdowns using two model suites. We investigated animal-level characteristics, while controlling for herd-level factors and clustering. We were interested in potential impacts of concurrent infection, and therefore we assessed whether animals with evidence of liver fluke infection (Fasciola hepatica; post-mortem inspection), M. avium reactors (animals with negative M. bovis-avium (b-a) tuberculin reactions) or Bovine Viral Diarrhoea Virus (BVDV; RT-PCR tested) were associated with bTB confirmation.ResultsThe dataset included 6242 animals removed during the 14 month study period (2013–2015). bTB-VL presence was significantly increased in animals with greater b-a reaction size at the disclosing SICCT test (e.g. b-a = 5-9 mm vs. b-a = 0 mm, adjusted Odds ratio (aOR): 14.57; p < 0.001). M. avium reactor animals (b-a < 0) were also significantly more likely to disclose VL than non-reactor animals (b-a = 0; aOR: 2.29; p = 0.023). Animals had a greater probability of exhibiting lesions with the increasing number of herds it had resided within (movement; log-herds: aOR: 2.27–2.42; p < 0.001), if it had an inconclusive penultimate test result (aOR: 2.84–3.89; p < 0.001), and with increasing time between tests (log-time; aOR: 1.23; p = 0.003). Animals were less likely to have VL if they were a dairy breed (aOR: 0.79; p = 0.015) or in an older age-class (e.g. age-quartile 2 vs. 4; aOR: 0.65; p < 0.001). Liver fluke or BVDV variables were not retained in either multivariable model as they were non-significantly associated with bTB-VL status (p > 0.1).ConclusionsOur results suggest that neither co-infection of liver fluke nor BVDV had a significant effect on the presence of VLs in this high-risk cohort. M. avium tuberculin reactors had a significantly increased risk of disclosing with a bTB lesion, which could be related to the impact of co-infection with M. avium subsp. paratuberculosis (MAP) affecting the performance of the SICCT however further research in this area is required. Movements, test history, breed and age were important factors influencing confirmation in high-risk animals.

Tuberculin Skin Testing Boosts Interferon Gamma Responses to DIVA Reagents in Mycobacterium bovis-Infected Cattle.

Mycobacterium bovis BCG vaccination sensitizes cattle to bovine tuberculin, which compromises the use of the current bovine tuberculosis (TB) surveillance tests. Although the performance of a blood test (that utilizes antigens expressed by Mycobacterium bovis but not by BCG) capable of discriminating infected from vaccinated animals (DIVA interferon gamma test [DIT]) has been evaluated in naturally infected TB field reactors, there is a need to perform similar analysis in a BCG-vaccinated M. bovis-infected population. Furthermore, we explored different scenarios under which a DIT may be implemented alongside BCG vaccination: (i) serial testing to resolve potential false-positive skin test results or (ii) a standalone test to replace the single intradermal comparative cervical tuberculin (SICCT) skin test. Our results demonstrated significantly better relative test sensitivity when the DIT was evaluated in a serial test scenario. Direct comparison of pre- and post-skin test blood samples revealed that the SICCT test induced significant boosting of the gamma interferon response in M. bovis-infected animals to both the ESAT-6-CFP-10 and Rv3615c peptide cocktails that comprise the DIT, which persisted for the ESAT-6-CFP-10 reagent for at least 14 days. Importantly, no similar boosting effects were observed in noninfected BCG vaccinates, suggesting that DIVA blood testing after a recent skin test would have minimal impact on test specificity.

Assessment of concurrent infection with bovine viral diarrhoea virus (BVDV) and Mycobacterium bovis: A herd-level risk factor analysis from Northern Ireland

Bovine viral diarrhoea virus (BVDV) is a significant pathogen of cattle, leading to severe economic and animal-welfare impacts. Furthermore, the pathogen has been associated with impacting the progression or spread of other pathogens (e.g. Mycobacterium bovis, the causative agent of bovine tuberculosis (bTB)). During this study we investigated (i) risk factors for BVDV at a herd-level and (ii) whether there was any association between BVDV and herd-level bTB risk.The data for this study were gathered from a voluntary BVDV control programme in Northern Ireland (2013–2015) based on the identification of virus positive animals through tissue tag testing of calves. We assigned a herd-level BVDV status to 2827 participating herds, where a herd was assumed “infected” if one or more animals tested positive for BVDV. Two model suites were developed. Firstly, we assessed risk factors for BVDV herd status using multivariable logit random-effects modelling, aggregating to the calendar year level (2013–2015; n=4828; model 1). Secondly, we aggregated data across the three years of the study to give an overall status for the whole study period (n=2827; logistic model 2). Risk factors included year, herd-type, herd size, number of births, inward trade moves, calf mortality, and region. Furthermore, the herd-level bovine tuberculosis status (based on the single intradermal comparative cervical tuberculin (SICCT) test outcomes, or confirmation at post-mortem), or the size of bTB breakdowns (number of SICCT test positive animals), of herds was also investigated to assess whether there was an association (co-infection) with herd BVDV status.The final models suggested that BVDV herd status was positively associated with increased levels of calf mortality, herd size, number of births, the number of BVDV tests undertaken and the number of animals introduced to the herd. There was a significant univariable positive association between BVDV status, and SICCT breakdown risk, breakdown size and confirmed bTB status in model 2. However, there was no evidence of significant associations between bTB status (using SICTT status, confirmed status or herd breakdown size) and BVDV status in final multivariable models when controlling for other significant confounders. These results provide information for action for the future control and eradication of BVDV in Northern Ireland, though these data provide little support for the hypothesised association between BVDV and bTB status at herd-level. Further animal-level analyses are necessary to investigate whether there is support for a BVD-bTB co-infection association, including the impact of co-infection on the severity of infection.

Responses to diagnostic tests for bovine tuberculosis in dairy and non-dairy cattle naturally exposed to Mycobacterium bovis in Great Britain

Field surveillance of British cattle using the single intradermal comparative cervical tuberculin (SICCT) test shows a higher incidence rate of bovine tuberculosis (bTB) in dairy compared to beef herds, but a lower probability of post-mortem examination confirmed (PMC) Mycobacterium bovis infection in dairy herds. A cross-sectional study was conducted to compare animal level differences in bTB detection between dairy and non-dairy cattle in Great Britain. During the period from 2002 to 2005, 200 (41% dairy) reactors in the SICCT test (standard interpretation) were randomly selected, and 200 in-contact cattle (43% dairy) were purposively selected from bTB-infected herds. Interferon (IFN)-γ responses in blood to bovine and avian purified protein derivative (PPD), and early secretory antigen target 6 kDa and culture filtrate protein 10 (ESAT-6/CFP10), were measured. The post-mortem examination included gross pathological examination, mycobacterial culture and histopathology. The proportions of cattle positive to ESAT6/CFP10 were 26% (95% confidence interval, CI, 15–39%) in dairy reactors and 62% (95% CI 51–72%) in non-dairy reactors (P < 0.001). PMC risk was 34% (95% CI 24–45%) in dairy reactors and 69% (95% CI 60–78%) in non-dairy reactors (P < 0.001). The odds ratio for PMC risk in dairy reactors compared to non-dairy reactors, after controlling for bTB prevalence, herd size and SICCT test response, was 0.27 (95% CI 0.14–0.53; P < 0.001). In surveillance data, adjusted animal level PMC risks were lower for dairy reactors than for beef reactors aged >2 years (P < 0.001).

Bovine Tuberculosis in East Africa

The zoonotic Mycobacterium bovis is a pathogen of significance in the dairy industry in many parts of the world. Although the pathogen primarily affects cattle, it has a wide host range including humans. A cross-sectional study was carried out in three agro-ecological zones of Tanzania, namely the southern highlands zone (SHZ), eastern zone (EZ) and northern zone (NZ), to examine the status of the disease in cattle, in order to inform control measures. A total of 391, 169 and 401 cattle were tested for bovine tuberculosis (bTB) in the SHZ, EZ and NZ respectively using the Single Intradermal Comparative Cervical Tuberculin Test (SICTT). Results showed that the prevalence of bTB was higher (P<0.05) in EZ 2.37% (n = 169) compared to SHZ 1.3% (n=391) and NZ, where no positive result was recorded (n = 401). Thirty three cattle from SHZ and seven from EZ showed inconclusive results. In Kenya, 625 cattle from four sites within agro-pastoral and pastoral production systems were tested. In one area of Mwingi County, eastern Kenya, all the 161 cattle tested negative; while in the other three sites of Migori, in Nyanza, West Pokot and Laikipia in the Rift Valley, prevalence of 4-6% was obtained with SICTT. Bovine TB occurs in the region and may pose a public health threat through occupational activities and/or consumption of animal products, especially since no obvious clinical signs were observed in positive animals. Policy issues on how to deal with positive cases, creation of awareness on this important zoonotic disease, and a simple test to quickly identify sick animals in the field require urgent attention. Key Words: Agro-ecological zones, Mycobacterium bovis , Zoonoses

Detection of Mycobacterium tuberculosis and Mycobacterium bovis in Sahiwal cattle from an organized farm using ante-mortem techniques.

Aim:The aim of this study was to investigate the prevalence of bovine tuberculosis (TB) and detection of Mycobacterium bovis in cattle from an organized dairy farm.Materials and Methods:A total of 121 animals (93 females and 28 males) of 1 year and above were studied for the prevalence of bovine TB using single intradermal comparative cervical tuberculin (SICCT) test, bovine gamma-interferon (γ-IFN) enzyme immunoassay, and polymerase chain reactions (PCRs).Results:Out of total 121 animals, 17 (14.04%) animals were positive reactors to SICCT test while only one (0.82%) animal for γ-IFN assay. By PCR, Mycobacterium TB complex was detected in 19 (15.70%) animals out of which 4 (3.30%) animal were also positive for M. bovis.Conclusions:Diagnosis of bovine TB can be done in early stage in live animals with multiple approaches like skin test followed by a molecular technique like PCR which showed promising results.