Caudal Fold Tuberculin Research Articles

An ELISA test using a circulating Mycobacterium bovis peptide for detecting bovine tuberculosis in dairy cattle.

This study aimed to determine the sensitivity (Se) and specificity (Sp) of a circulating pathogen-specific biomarker (polyketide synthetase 5, Pks5)-based enzyme-linked immunosorbent assay (ELISA) independently or in conjunction with a caudal fold tuberculin (CFT) test for bovine tuberculosis (bTB) screening in dairy cattle. We enrolled 987 dairy cows from 34 herds in Chiang Mai province, Thailand. A conditionally independent Bayesian model with a single population was inferred from the test results. The percentage of positive results for the Pks5-ELISA using 0.4 OD cutoff test and CFT test were 9.0% (89/987) and 10.5% (104/987), respectively. The median of posterior estimates of Se for the Pks5-ELISA test was 90.2% (95% posterior probability interval [PPI] = 76.6-97.4%), while the estimated Sp was slightly higher (median = 92.9, 95% PPI = 91.0-94.5%). The median estimated Se of the CFT test was 85.9% (95% PPI = 72.4-94.6%), while the estimated Sp was higher, with a median of 90.7% (95% PPI = 88.7-92.5%). The posterior estimate for true disease prevalence was 2.4% (95% PPI = 1.2-3.9%). The Pks5-ELISA test yielded characteristics at or above the acceptable standards for bTB detection. Therefore, the pathogen-specific biomarker, Pks5, is a potential detection system for bTB screening and may be applied as an ancillary test together with the currently applied standard method (CFT test) to reinforce the bTB control and eradication programs.

Very low prevalence of bovine tuberculosis in cattle in Sylhet district of Bangladesh

Bovine tuberculosis (bTB), a chronic zoonotic disease in cattle, has a substantial socio-economic and public health impact. This study was conducted to estimate the prevalence and geographical distribution of bTB in the Sylhet district of Bangladesh. A cross-sectional study was conducted at all 12 upazilas of Sylhet district, which included 512 randomly selected cattle from 48 farms. Selected animals were tested with the Caudal Fold Tuberculin (CFT) test to identify bTB-positive cattle. Out of 512 cattle, only one animal was identified as a reactor, providing an estimated prevalence of 0.19% (95% Confidence Interval; 0–0.58%). The only positive reactor was found in Zakiganj upazila. As the prevalence of bTB in cattle in Sylhet appears to be low, it indicates that most of the upazilas of Sylhet district are free of the bTB infection. This prevalence is lower than the reported prevalence in other parts of Bangladesh. Thus, attempts should be made to maintain the current situation of bTB infection in cattle of Sylhet district.

Host Serum Proteins as Potential Biomarkers of Bovine Tuberculosis Resistance Phenotype.

Eradication of bovine tuberculosis (bTB) continues to be a worldwide challenge. The lack of reliable vaccines dampens the control and eradication programs of Mycobacterium bovis infection and spread. Selection and breeding of cattle resistant to M. bovis infection would greatly enhance the effectiveness of bTB eradication programs. Here, we have evaluated the potential of serum proteins as biomarkers of cattle resistance to bTB in Holstein-Friesian cows, 6–8-year-old, born and raised in similar conditions in herds with bTB prevalence >30%. Serum proteins obtained from uninfected cows (bTB-resistant; R) were compared to those from infected cows (bTB-susceptible; S), defined by a negative or positive bTB diagnosis, respectively. bTB diagnosis included: (i) single intradermal (caudal fold) tuberculin test, (ii) whole blood IFN-gamma test, (iii) gross visible lesions in lymph nodes and lungs by inspection at the abattoir, and (iv) a bacteriological culture for M. bovis. Using 2D-GE and LC-ESI-MS/MS, we found higher expression levels of primary amine oxidase (AO), complement component 5 (C5), and serotransferrin (TF) in R cattle than S cattle. In-house developed and standardized ELISAs for these novel biomarkers showed the best sensitivities of 72, 77, 77%, and specificities of 94, 94, 83%, for AO, C5, and TF, respectively. AUC-ROC (95% CI) values of 0.8935 (0.7906–0.9964), 0.9290 (0.8484–1.010), and 0.8580 (0.7291–0.9869) were obtained at cut-off points of 192.0, 176.5 ng/ml, and 2.1 mg/ml for AO, C5, and TF, respectively. These proteins are involved in inflammatory/immunomodulatory responses to infections and may provide a novel avenue of research to determine the mechanisms of protection against bTB. Overall, our results indicate that these proteins could be novel biomarkers to help identify cattle resistant to bTB, which in turn could be used to strengthen the effectiveness of existing eradication programs against bTB.

Evaluation of a virulent strain of Mycobacterium avium subsp. Paratuberculosis used as a heat-killed vaccine

Bovine paratuberculosis is one of the most important chronic infectious diseases in livestock. This disease is difficult to control because of its inefficient management (test and cull strategy and inadequate biosecurity). Thus, the development of an effective vaccine is essential. In this study, we evaluated a local virulent strain (6611) of Mycobacterium avium subsp. paratuberculosis as an inactivated vaccine in comparison with the Silirum vaccine in mouse model and cattle. Regarding the mice model, only the groups vaccinated with 6611 showed lower colony forming unit (CFU) counts with a lower lesion score in the liver in comparison to the control group at 6 and 12 weeks post-challenge (wpc). The immune response was predominantly humoral (IgG1), although both vaccinated groups presented a cellular response with IFNγ production as well, but the 6611 group had also significant production of IL-2, IL-6, IL-17a, TNF, and IL-10. In cattle, the 6611 vaccinated group was the only one that maintained significant antibody values at the end of the trial, with significant production of IgG2 and IFNγ. No PPDb reactor was detected in the vaccinated animals, according to the intradermal caudal fold tuberculin test. Our results indicate that the 6611 local strain protected mice from challenge with a virulent strain, by inducing a humoral and cellular immune response. In the bovine, the natural host, the evaluated vaccine also induced humoral and cellular immune responses, with higher levels of CD4 + CD25+ and CD8 + CD25+ T cells populations than the commercial vaccine. Despite the encouraging results obtained in this study, an experimental challenge trial in cattle is mandatory to evaluate the efficacy of our candidate vaccine in the main host.

SCREENING TEST FOR BOVINE TUBERCULOSIS AMONGST CATTLE POPULATION IN ZARIA AREA USING SINGLE CAUDAL-FOLD TECHNIQUE.

Five hundred out of 732 heads of cattle in twenty selected birds in Zaria and its environs, were screened for tuberculosis using the single caudal fold (SCF) tuberculin test. Fifty nine (11.8%) beads of cattle were detected to be reactors, while 43 (8.6%) and 398 (79.6%) were suspects and non-reactors respectively. Only one herd had no reactors nor suspects. Amongst reactors, the incidence increased with age, with 6.9% reactors in 0-1 year age group; while those over 5 years old had 28 (20.9%) reactors. The difference was statistically significant (P<0.05;x2) Management system had an effect on the incidence of tuberculin test reactors with purely nomadic animals showing a greater number of reactors (72.88%) than intensively (0.0%) and semi-intensively (27.12%) managed farms, Sex had no effect on reactor rates as 13(11.4%) of 114 males and 46 (11.9%) of 386 females were reactors. The difference was not statistically significant(P<0.05;x2). It is therefore concluded that cattle in nomadic Fulani herds harbour Mycobacteria which serve as a potential source of tuberculosis to man and other animals.

COMPARISON OF HEMATO-BIOCHEMICAL PARAMETERS BETWEEN APPARENTLY HEALTHY AND BOVINE TUBERCULOSIS AFFECTED CATTLE IN CHITTAGONG, BANGLADESH

The cross-sectional study was carried out to compare the hematological and serum biochemical profiles between bovine tuberculosis (bTB) affected and apparently healthy cattle during the period from March 2014 to October 2016. A total of 189 blood samples were collected from 93 bTB affected and 96 apparently healthy cattle of 3 Upazilas of Chittagong. The bovine tuberculosis (bTB) was diagnosed primarily by Caudal Fold Tuberculin Tests (CFTT) and confirmed by the Comparative Intradermal Tuberculin Test (CITT). The whole blood was analyzed for hematology, and serum samples were used for biochemical analysis. The study revealed that, the values for TEC, Hb and PCV were higher in infected cohort (based on CFTT) in compare to their counterpart control group. Among these three parameters only PCV values were statistically significant (P ≤ 0.05). Only basophil percentage was significantly (P ≤ 0.05) higher in infected cohort. The values of total protein, albumin, creatinine and SGOT were insignificantly lower and the values of calcium & phosphorus were also insignificantly higher in bTB affected cattle than control group of cattle.

Exploring the association between polymorphisms at 3’UTR SLC11A1 gene microsatellites and resistance to tuberculosis: A case-control study in Bos taurus dairy cattle

Bovine tuberculosis is a contagious infectious disease that causes significant economic impact in dairy and meat farms throughout the world. Multiple factors, including host genome, determine the outcome of the infection. Several studies have associated polymorphisms at the two microsatellites (Ms) -Ms1 and Ms2- at the 3´unstranslated (UTR) region of the SLC11A1 bovine gene with innate resistance or susceptibility to some facultative intracellular bacterial infections, such as Brucella abortus and Mycobacterium avium subsp. paratuberculosis. Today, the few studies that investigated the association of those polymorphisms with innate resistance or susceptibility to tuberculosis in cattle, have shown opposite results. The aim of this study was to evaluate the role, if any, of the Ms1 and/or Ms2 polymorphisms at the 3´UTR of the SLC11A1 gene in Mycobacterium bovis infection phenotypes in Bos taurus dairy cattle. Jersey (n = 149) and Holstein (n = 427) cattle under risk of natural M. bovis infection were classified like controls (n = 326) and cases (n = 250) based on the response to caudal fold tuberculin skin test. Cattle population was genotyped by capillary electrophoresis based on polymorphisms in Ms1 and Ms2 at the 3´UTR SLC11A1 gene. The results presented here showed a lack of association (p > .05) between polymorphisms at the 3´UTR SLC11A1 gene and the response to tuberculin skin test in dairy Bos taurus cattle. Further studies are necessary to establish robustly genes or genome regions determining the innate R/S phenotype to Mycobacterium bovis.

Comparison of common tests performance for Mycobacterium bovis infection diagnosis in low prevalence dairy cattle herds of southern Chile

ABSTRACT: The aim of the present study was to assess the performance of routinely used diagnostic tests to detect M. bovis infection in cattle populations with very low infection prevalence. A cross-sectional study was performed using 609 animals from 17 herds that were sampled for blood interferon, and tested with the caudal fold tuberculin test (CFT). It was planned that animals which showed CFT positive results were sent to the slaughterhouse for post mortem confirmation testing. However, not all the animals considered in the initial sampling were culled. Paired population proportions of positive results for the different diagnostic tools were compared. Apparent sensitivity and specificity was also estimated. Overall, intradermal tuberculin based diagnostics showed better performance in comparison to interferon based test, even though interferon was slightly more specific. From these results, it may be suggested that specific cut-off lines for interferon based techniques for certain areas with particular low bTB prevalence should be considered, as well as the modification of more specific antigens and the use of better combinations of PPDs if in vitro testing is intended must be taken into consideration. The uncertain role of interference bacteria that could be affecting the results of the in vitro analysis must be considered, and perhaps this could explain the apparent lack of consensus of the results obtained in Chile versus the ones obtained elsewhere. More studies must be performed in order to assess this issue.

Cross sectional study of bovine and avian tuberculosis in Bangladesh Livestock Reasearch Institute (BLRI) cattle farm

The present study was carried out to determine the prevalence of bovine and avian tuberculosis in cattle by using bovine and avian PPDs at Bangladesh Livestock Research Institute (BLRI) Cattle Farm, Savar, Dhaka. Cattle of different breeds, ages and sexes (n=183) were tested using bovine and avian PPDs. In caudal Fold Tuberculin (CFT) test, 16 (8.74%) cases were showed positive reaction among 183 sample. The overall percentages of positive reactors to Comparative cervical tuberculin (CCT) test of bovine and avian tuberculosis were 7.10% and 1.64% respectively. An insignificant variation (P>0.05) on prevalence of bovine tuberculosis on different age group of cattle was observed. Age group >7 years showed a higher prevalence (10.91%) than those of other age groups. In CCT test, 7.55% and 4.17% positive reactors were found in female and male cattle respectively. The association between different breeds of the animal was found significant (P<0.05). The local breed showed higher prevalence (9.77%) than those of Red Chittagong and cross breed. The highest percentage (10.45%) of positive reactors in CCT test was recorded in milking cows than in dry cows (2.32%), heifer (9.52%) and calf (5.77%) were observed. Mixed infection (bovine and avian type of tuberculosis) was recorded 1.64%.Asian J. Med. Biol. Res. September 2017, 3(3): 352-356

Screening food-borne and zoonotic pathogens associated with livestock practices in the Sumapaz region, Cundinamarca, Colombia

Hazardous practices regarding antibiotics misuse, unsanitary milking procedures, and the commercial sales of raw milk and unpasteurized dairy products are currently being practiced by livestock farmers in the Sumapaz region (Colombia). The purpose of this study was to screen for food-borne and zoonotic pathogens associated with local livestock practices. We evaluated 1098 cows from 46 livestock farms in the Sumapaz region that were selected by random. Of the total population of cattle, 962 animals (88%) were tested for bovine TB using a caudal-fold tuberculin test and 546 (50%) for brucellosis by a competitive ELISA. In the population tested, 23 cows were positive for Brucella sp. representing a 4.2% seroprevalence and no cases of bovine tuberculosis were found. In addition, food-borne contamination with Escherichia coli and Staphylococcus aureus was assessed together with antibiotic susceptibility for ten different antibiotics in milk samples from 16 livestock farms. We found that 12 of the farms (75%) were contaminated with these food-borne pathogens. Noteworthy, all of the isolated pathogenic strains were resistant to multiple antibiotics, primarily to oxytetracycline and erythromycin. Our findings suggest that livestock products could be a source of exposure to Brucella and multidrug-resistant E. coli and S. aureus strains as a result of unhygienic livestock practices in the Sumapaz region. Training in good farming practices is the key to improving safety in food production.

Prevalence of Mycobactrium Bovis Infection in Cattle Based on Intra-Dermal Caudal Fold Tuberculin Test in Adamawa State, Nigeria

A cross sectional survey was carried out using convenient sampling technique to sample 79 herds comprising of 2, 810 cattle in 5 Local Government Areas (L.G.A) of Adamawa State in the North East of Nigeria. This was based on the availability of cattle populations, physical accessibility to the herds, availability of cattle restraint facilities and consent of the cattle owners. Purified Protein Derivative (PPD) purchased from Prionics Lelystad, Prod. Nr. 7600040 in the Netherlands was used in screening the cattle for M. bovis infection using intra-dermal caudal fold tuberculin test. The result after 72 hours indicated an overall prevalence of 8.4% (236/2, 810) with Mayo-Belwa L.G.A having the highest prevalence of 19.2% (117/610) while no cattle reacted to the test in Girei L.G.A. It was concluded that this result may serve as a base line data on the status of M. bovis infection in cattle in Adamawa State, as such there is the need to extend this study in all the L.G.As of Adamawa State. This recommendation may require legislative action in order to compel the herdsmen to present their cattle for testing.

Association between caudal fold tuberculin test responses and results of an ELISA for Mycobacterium avium subsp paratuberculosis and mycobacterial culture of feces in tuberculosis-free dairy herds

OBJECTIVE--To evaluate associations between Mycobacterium avium subsp paratuberculosis (MAP) and caudal fold tuberculin (CFT) test results in cattle. DESIGN--Longitudinal and cross-sectional evaluations. ANIMALS--1 California (approx 3,600 cows) and 3 Colorado (approx 640, 1,190, and 1,480 cows) dairy herds considered free of Mycobacterium bovis infection. PROCEDURES--In the California herd, the association between CFT response and MAP status was determined with ELISA and mycobacterial culture of feces within 1 year before and after CFT testing. The association between CFT and MAP status in all herds was modeled with mixed-effects logistic regression. RESULTS--In the California herd, significantly higher odds of being classified as suspect by CFT were found for cows with results of MAP ELISA negative before and positive after CFT testing (OR, 5.6) and cows positive before and after CFT testing (OR, 8.1). Higher odds were found for cows positive for mycobacterial culture of feces before and negative for culture after CFT testing (OR, 4.6) and cows negative for mycobacterial culture of feces before and positive for culture after CFT testing (OR, 13.2). All herds had higher odds of being classified as suspect by CFT testing for cows with positive results for ELISA (OR, 2.9) or mycobacterial culture of feces (OR, 5.0), compared with cows with negative results of the same tests. CONCLUSIONS AND CLINICAL RELEVANCE--A strong association was found between positive MAP test results and being classified as a suspect by CFT testing. Within-herd MAP prevalence may affect specificity of CFT testing for tuberculosis in cattle.

A Cross Sectional Study on Prevalence of Bovine Tuberculosis of Buffaloes in Bangladesh

This study was conducted to determine the prevalence of bovine tuberculosis in buffalo population in Bangladesh by Caudal Fold Tuberculin (CFT) test using bPPD and also by Comparative Cervical Tuberculin (CCT) test using both bPPD and aPPD. The percentage of reactors was 6.12% in CFT, whereas the percentage of positive buffaloes was 4.08% by CCT method. The percentage of suspicious buffaloes was 10.20% by CFT. On the other hand, all the suspicious cases were proved as misleading-false-reactions in CCT. By CCT method, the male buffaloes (6.25%) showed more positivity to tuberculosis than the female buffaloes (3.03%) of the same area. In contrast, the result found by CFT method was more or less similar (20%) for both male and female buffaloes. Young buffaloes (6-30 months) were more susceptible to tuber-culosis than older buffaloes. It might be suggested that a well coordination in activities should be taken among the public health and Veterinary public health organelles for complete eradication of the disease from the country.DOI: http://dx.doi.org/10.3329/mh.v1i1.13709 Microbes and Health Vol.1(1) June 2012 pp.23-26

Prevalence of bovine and avian tuberculosis in sheep and goat population of Bangladesh

An attempt was undertaken to investigate the occurrence of bovine and avian tuberculosis in sheep and goat population in Bangladesh. A total of 273 sheep and 155 goats were screened for bovine and avian tuberculosis by caudal fold tuberculin (CFT) and comparative cervical tuberculin (CCT) tests. The percentage of responders to CFT test in sheep and goat were 9.15% and 1.29% respectively. The overall percentage of reactors to CCT test in sheep and goats were 1.46% and 1.29% respectively. In CCT test the reactors were 0.36%, 1.29% for bovine tuberculosis, 1.09%, 1.29% for avian tuberculosis and 0.00%, 1.29% for mixed type for the sheep and goats respectively. In sheep of 3-4 years of age the reactors were 2.39 times higher than sheep below 3 years of age. In goats of 4.1-6 years of age the reactors were 2.40 times higher than goats below 3 years of age. The present prevalent study showed significant ( P 0.05) association in sheep. In sheep the percentages of reactors were 1.24 times higher in male (1.72%) than female (1.39%). Jamunapari (2.85%) breed of goat had 3.5 times higher percentage of reactors as compared to Black Bengal breed (0.83%). The study indicates that bovine and avian tuberculosis may cause dangerous effects on human health as well as livestock of Bangladesh so its prevention and eradication steps must be taken without any delay.

Surveillance for Mycobacterium bovis transmission from domestic cattle to wild ruminants in a Mexican wildlife-livestock interface area

To assess the prevalence of Mycobacterium bovis infection in cattle and wild ruminants (WRs) in a wildlife-livestock interface area (WLIA) of the Mexican highland plateau. 24,400 cattle from 793 herds (including 17,351 commercially slaughtered cattle) and 142 WRs (110 white-tailed deer [Odocoileus virginianus], 20 red deer [Cervus elaphus], and 12 North American elk [Cervus canadensis]) harvested via controlled hunting. Cattle were serially tested for M bovis infection via caudal fold tuberculin and comparative cervical tuberculin tests during field surveillance. Carcasses of cattle and WRs were inspected for gross lesions; samples suggestive of tuberculosis were analyzed via histologic evaluation and mycobacterial culture (HMC). A PCR assay to detect Mycobacterium tuberculosis complex organisms was performed to confirm positive results of HMC. WRs had inflammatory lesions in lungs and lymph nodes, although HMC results did not indicate M bovis infection. Eight cattle had positive results for both tuberculin tests, and 31 had positive results for HMC of grossly detected lesions; all were from 7 herds, and ≥ 1 cow in each herd had positive PCR assay results. These 7 herds were depopulated; adjacent herds and herds related via commerce were quarantined. Calculated true prevalence of M bovis infection was 0.86% (95% confidence interval, 0.24% to 1.49%) in cattle; M bovis was not detected in any WRs. M bovis infection was present in cattle. Although transmission to WRs in this WLIA was not detected, diagnosis and prevention activities should be implemented and consolidated to prevent potential M bovis transmission between cattle and WRs.

Meta-analysis of field studies on bovine tuberculosis skin tests in United States cattle herds

Our objective was to summarize information on the diagnostic accuracy, in terms of test sensitivity (Se) and specificity (Sp), for bovine tuberculosis (bTb) tuberculin skin tests as currently used in the United States. Meta-analyses including Se and Sp estimates from field studies of bTb tuberculin tests conducted in North American cattle were conducted to provide a distribution of estimates and central tendency for Se and Sp of the caudal fold tuberculin (CFT) and serial interpretation of the CFT and comparative cervical tuberculin (CFT-CCT) tests. In total, 12 estimates for CFT and CFT-CCT test Se and Sp were identified from seven publications matching inclusion criteria. Estimates for CFT test Se ranged from 80.4% to 93.0% and CFT test Sp from 89.2% to 95.2%. Estimates for CFT-CCT test Se ranged from 74.4% to 88.4% and CFT-CCT test Sp ranged from 97.3% to 98.6%. These distributions of test Se and Sp are intended to provide a more realistic representation for U.S. bTb skin tests than previously reported. Estimation and discussion of herd-level CFT and CFT-CCT test parameters is also included. These results should be considered at the herd and individual animal level when evaluating results from tuberculin skin test results in North American cattle herds.

Tuberculose bovina no Estado da Paraíba: estudo retrospectivo

O objetivo do presente trabalho foi determinar a frequência de propriedades positivas (focos) e de animais positivos para a tuberculose bovina no Estado da Paraíba. Foram utilizados dados da Agência de Defesa Agropecuária do Estado, coletados de suas 23 microrregiões, durante o período de janeiro de 2008 a julho de 2009. Durante esse período, foram examinadas 10.963 propriedades e 54.472 bovinos foram submetidos ao teste de tuberculinização. Para o diagnóstico foi utilizada, como prova de triagem, a tuberculinização cervical simples para gado de leite e a tuberculinização na prega caudal para gado de corte; como prova confirmatória foi utilizada a tuberculinização cervical comparativa. Uma propriedade foi considerada foco quando apresentou pelo menos um animal soropositivo. Das propriedades investigadas, 62 (0,57%) apresentaram pelo menos um animal positivo e dos animais analisados, 136 (0,25%) foram positivos. Houve diferença significativa (p<0,001) na proporção de fêmeas (0,32%) e machos (0,04%) positivos. A despeito da baixa freqüência de focos de brucelose e de animais soropositivos, é necessária a condução de medidas que incluem a conscientização dos produtores, fiscalização nas barreiras sanitárias e levantamentos periódicos da situação epidemiológica desta doença, principalmente nas microrregiões com maior frequência da infecção, com o objetivo de evitar, ou pelo menos minimizar, a disseminação do agente.

Prevalência de tuberculose no rebanho bovino de Mossoró, Rio Grande do Norte

A tuberculose bovina é uma doença infecciosa crônica e debilitante que pode infectar humanos. Uma importante etapa para o controle é a determinação da prevalência nos rebanhos. O objetivo do presente trabalho foi determinar a prevalência da tuberculose bovina em Mossoró, RN. Inicialmente foi realizada uma avaliação de risco para a ocorrência da tuberculose bovina em 21 propriedades da região avaliada. Foram testadas 150 vacas leiteiras por meio do teste da prega caudal. Também foram avaliados outros 120 bovinos pelo teste da tuberculinização cervical comparada. Os resultados revelaram falta de conhecimento dos proprietários sobre o controle da doença, bem como o descuido no momento da aquisição de animais. A prevalência foi de 8,66% e 3,33% nos testes da prega caudal e cervical comparativo, respectivamente. Assim, foi verificada uma prevalência de tuberculose bovina bastante elevada, sendo superior à média nacional.

Herd and Spatial Factors Affecting the Proportion of False-Positive Results on the Caudal Fold Tuberculin Test in Michigan Cattle

Bovine tuberculosis skin tests have been used successfully for control and eradication of bovine tuberculosis in the United States since the eradication program was begun in 1917. In 1992, there were only 10 states that had not achieved tuberculosis-free status. Unfortunately, bovine tuberculosis has become endemic in the cattle population in certain areas in the United States, including the northern part of the Michigan's Lower Peninsula. The caudal fold test is a key element of herd-level and individual animal screening. The specificity of the caudal fold tuberculin test is not perfect, and has been estimated to be approximately 89-96%. It is also evident that the specificity of the caudal fold tuberculin test is not a constant in different cattle populations. Variation in specificity may be due to differences in the amount and concentration of the tuberculin used for the test, regional variation in cross-reacting mycobacteria that cause false-positive results on the caudal fold tuberculin test, and variation in the interpretation of the test results by the testing veterinarians. The objective of this study was to use available data from the bovine tuberculosis testing program in Michigan to evaluate possible associations between the proportion of false-positive results on the caudal fold tuberculin test, and factors regarding geography and type of herd.

Use of simulation modeling to estimate herd-level sensitivity, specificity, and predictive values of diagnostic tests for detection of tuberculosis in cattle

To estimate herd-level sensitivity (HSe), specificity (HSp), and predictive values for a positive (HPVP) and negative (HPVN) test result for several testing scenarios for detection of tuberculosis in cattle by use of simulation modeling. Empirical distributions of all herds (15,468) and herds in a 10-county area (1,016) in Michigan. 5 test scenarios were simulated: scenario 1, serial interpretation of the caudal fold tuberculin (CFT) test and comparative cervical test (CCT); scenario 2, serial interpretation of the CFT test and CCT, microbial culture for mycobacteria, and polymerase chain reaction assay; scenario 3, same as scenario 2 but specificity was fixed at 1.0; and scenario 4, sensitivity was 0.9 (scenario 4a) or 0.95 (scenario 4b), and specificity was fixed at 1.0. Estimates for HSe were reasonably high, ranging between 0.712 and 0.840. Estimates for HSp were low when specificity was not fixed at 1.0. Estimates of HPVP were low for scenarios 1 and 2 (0.042 and 0.143, respectively) but increased to 1.0 when specificity was fixed at 1.0. The HPVN remained high for all 5 scenarios, ranging between 0.995 and 0.997. As herd size increased, HSe increased and HSp and HPVP decreased. However, fixing specificity at 1.0 had only minor effects on HSp and HPVN, but HSe was low when the herd size was small. Tests used for detecting cattle herds infected with tuberculosis work well on a herd basis. Herds with < approximately 100 cattle should be tested more frequently or for a longer duration than larger herds to ensure that these small herds are free of tuberculosis.