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The objective of this cross-sectional study was to estimate familial associations with paratuberculosis ELISA status in beef cattle. Texas Longhorn cattle (n=715) greater than 2years of age were sampled for paratuberculosis testing using ELISA and fecal culture. Diagnostic test results were indicative of substantial numbers of false-positive serological reactions consistent with environmental exposure to non-MAP Mycobacterium spp. Associations between ancestors and paratuberculosis ELISA status of offspring were assessed using conditional logistic regression. The association between ELISA status of the dam and her offspring was assessed using linear mixed-effect models. Significant associations were identified between some ancestors and offspring ELISA status. The odds of being classified as "suspect" or greater based on ELISA results were 4.6 times greater for offspring of dams with similarly increased S:P ratios. A significant positive linear association was also observed between dam and offspring log-transformed S:P ratios. Results indicate that there is familial aggregation of paratuberculosis ELISA results in beef cattle and suggest that genetic selection based on paratuberculosis ELISA status may decrease seroprevalence. However, genetic selection may have minimal effect on paratuberculosis control in herds with exposure to non-MAP Mycobacterium spp.

Six hundred and sixty-eight dairy cattle were tested for Johne's disease using a direct-fecal real-time polymerase chain reaction (rt-PCR), fecal culture, and serum enzyme-linked immunosorbent assay (ELISA). Likelihood ratios (LRs) were estimated for five categories of sample-to-positive (S/P) values for the ELISA: <0.1, 0.1-0.249, 0.25-0.399, 0.4-0.999, > or =1.0. The statistical method assumed a single multinomial model for cross-classified rt-PCR, fecal culture results, and ELISA category strata. Conditional dependence between tests was investigated by the inclusion of all possible pairwise dependence terms. Sensitivity covariance between ELISA and fecal culture was estimated as 0.017. Estimates for the accuracy of the ELISA at the usual cutoff of 0.25S/P was 67.2% and 95.2% for sensitivity and specificity, respectively for a model that adjusted for the dependence between ELISA and fecal culture. The area under the receiver-operating characteristic (ROC) curve (95% probability interval) for the ELISA was 0.867 (0.796, 0.928). Point estimates for likelihood ratios (95% probability intervals) were 0.24 (0.11, 0.38), 1.52 (0.48, 3.27), 2.49 (0.31, 13.4), 6.33 (2.54, 16.5), and 103 (25.0, 2412) for the categories <0.1, 0.1-0.249, 0.25-0.399, 0.4-0.999, >/=1.0, respectively. Assumptions concerning the underlying distribution of test results for infected and uninfected animals were not necessary and this model can be employed for the general estimation of LRs and ROC curves in absence of knowledge concerning true disease status.

Objective: To evaluate the seroprevalence of paratuberculosis by use of 2 commercial ELISAs in association with prevalence of fecal shedding of mycobacteria within beef cattle herds., Design: Cross-sectional field study., Animals: Six beef herds (affected herds; 522 cattle) with and 3 geographically matched herds (181 cattle) without high seroprevalence of paratuberculosis., Procedures: Blood and fecal samples were collected from adult cattle and assessed for serum anti-Mycobacterium avium subsp paratuberculosis (MAP) antibodies with 2 commercial ELISA kits and submitted for bacterial culture for MAP and environmental bacteria (termed environmental mycobacteria) via a radiometric method, respectively. Species of mycobacterial isolates were identified, and sensitivities and specificities of the 2 ELISAs were compared., Results: Compared with comparison cattle, cattle from affected herds were 9.4 times as likely to have environmental mycobacteria isolated from feces. Among the 6 affected and 3 comparison herds, the proportions of cattle shedding environmental mycobacteria were 0.225 (range, 0.1 to 0.72) and 0.04 (range, 0 to 0.06), respectively. Although relative MAP- detection specificities (compared with bacterial culture of feces) were different between the 2 ELISAs, sensitivities were not. Nine environmental mycobacterial species were identified from participating herds. All affected herds apparently had > or = 1 bovid infected with MAP, although MAP was not isolated from any cattle in comparison herds., Conclusions and Clinical Relevance: In beef herds with persistently high rates of false- positive ELISA results, which may be associated with recovery of environmental myco- bacteria from feces, organism detection via bacterial culture of feces or PCR assay should direct paratuberculosis control measures.

Objective: To evaluate the effect of exposure to environmental mycobacteria on results of 2 commercial ELISAs for paratuberculosis in cattle., Design: Experimental trial., Animals: 19 weaned crossbred beef calves., Procedures: Calves were inoculated SC with 1 of 5 mycobacterial isolates (3 calves/isolate) derived from herds with high proportions of false-positive serologic reactions for paratuberculosis, Mycobacterium avium subsp paratuberculosis (MAP; positive control inoculum; 2 calves), or mineral oil (negative control inoculum; 2 calves). Sera were assessed at intervals by use of 2 ELISAs (A and B) for paratuberculosis in cattle, and all calves underwent tuberculosis testing at the end of the study., Results: Neither mineral oil-inoculated calf had positive results with either ELISA during the study. Both MAP-inoculated calves were identified as seropositive via ELISA-A, and 1 calf was identified as seropositive via ELISA-B. By use of ELISA-A, > or = 1 false-positive reaction over time was detected in 2, 3, 3, and 1 of the 3 calves injected with Mycobacterium avium, Mycobacterium intracellulare, Mycobacterium scrofulaceum, or Mycobacterium terrae, respectively. By use of ELISA-B, only M scrofulaceum induced false-positive reactions (2/3 calves). Calves that had at least 1 positive ELISA-A result were more likely to be classified as suspect reactors via the caudal fold tuberculosis test., Conclusions and Clinical Relevance: False-positive serologic reactions may occur during use of commercially available ELISAs for paratuberculosis in calves experimentally exposed to environmental mycobacteria; naturally occurring exposures with these mycobacteria may represent a cause for high proportions of false-positive serologic reactions for paratuberculosis in some cattle herds.

Objective: To estimate the sensitivity (Se) and specificity (Sp) for an enhanced direct-fecal PCR procedure, bacterial culture of feces (BCF), and a serum ELISA for detecting Mycobacterium avium subsp paratuberculosis (MAP) infection in adult dairy cattle., Sample Population: Fecal and serum samples were collected from 669 adult cattle randomly selected from a 4,000-cow dairy herd known to contain animals infected with MAP., Procedures: Serum samples were evaluated for MAP-specific antibodies via ELISA. Fecal samples were evaluated by BCF and enhanced PCR methods (both gel-based [GB]-PCR and quantitative real-time [qRT]-PCR assays). Fecal samples also were pooled (5:1) and then subjected to GB-PCR assay. Bayesian statistical methods were used to estimate Se and Sp for each diagnostic test without knowledge concerning true MAP infection status., Results: Adjusting for Se conditional dependence between serum ELISA and BCR, overall Se and Sp were estimated at 33.7% and 95.9%, 51.3% and 99.0%, and 32.2% and 100% for serum ELISA, qRT-PCR, and BCF, respectively.The GB-PCR assay yielded positive results for 38.3% of the pools known to contain feces from at least 1 cow that had positive GBPCR results., Conclusions and Clinical Relevance: Estimated Se values for the serum ELISA and BCF were slightly lower than those reported elsewhere. The enhanced qRT-PCR method offered relative improvements in Se of 52% and 59% over serum ELISA and microbial culture, respectively. Pooling of fecal samples and testing with the GB-PCR assay are not recommended. Additional studies with qRT-PCR and fecal pools are required.

Objective: To estimate receiver-operating characteristic (ROC) curves for a competitive ELISA (c-ELISA) that is used in serodiagnosis of brucellosis in water buffalo and cattle, to determine the most appropriate positive cutoff value for the c-ELISA in confirmation of infection, and to evaluate species differences in c-ELISA function., Sample Population: Sera from 4 herds of cattle (n = 391) and 4 herds of water buffalo (381)., Procedure: Serum samples were evaluated for Brucella-specific antibodies by use of a c-ELISA. On the basis of previous serologic test results, iterative simulation modeling was used to classify animals as positive or negative for Brucella infection without the use of a gold standard. Accuracy of c-ELISA for diagnosis of infection was compared between cattle and water buffalo by comparison of areas under ROC curves., Results: A positive cutoff value of 30% inhibition for c-ELISA yielded sensitivity and specificity estimates, respectively, of 83.9 and 92.6% for cattle and 91.4 and 95.4% for water buffalo. A positive cutoff value of 35% inhibition yielded sensitivity and specificity estimates, respectively, of 83.9 and 96.2% for cattle and 88.0 and 974% for water buffalo. Areas under ROC curves were 0.94 and 0.98 for cattle and water buffalo, respectively., Conclusions and Clinical Relevance: ROC curves can be estimated by use of iterative simulation methods to determine optimal cutoff values for diagnostic tests with quantitative outcomes. A cutoff value of 35% inhibition for the c-ELISA was found to be most appropriate for confirmation of Brucella infection in cattle and water buffalo.

Fasciolosis causes significant economic losses in commercial cattle herds in South Africa, but its prevalence is unknown in most communal areas. A cross-sectional study was conducted with the aim of determining the occurrence of bovine fasciolosis using three different diagnostic methods in Moretele Local Municipality in Bojanala District, North West Province. Faecal samples were collected from 277 cattle of different breeds, ages, sex and faecal condition scores and examined using the sedimentation technique, quantitative real-time polymerase chain reaction (qPCR) and faecal antigen enzyme-linked immunosorbent assay (coproELISA). All samples were negative for bovine fasciolosis using coproELISA. A total of 73 (26.4%) samples were positive using the qPCR, while 36 were positive using the sedimentation technique, with low faecal egg counts (1 to 20 eggs per gram). The qPCR detected the highest positivity (26.4%, 95% CI 21.3, 32.0) followed by the sedimentation test (13.0%; 95% CI 9.3, 17.5). Location, breed, sex, age and faecal consistency score were not associated with positive qPCR results (p > 0.05). There was also no significant agreement (kappa = −0.011, p = 0.843) between qPCR and the sedimentation technique for the detection of Fasciola spp. The qPCR appeared to be the most sensitive method for detection of Fasciola spp. Further studies are required on the characterisation of Fasciola spp. in communal cattle in South Africa. [ABSTRACT FROM AUTHOR]

Objective--To compare calf weaning weight and associated economic variables for beef cows with serum antibodies against Mycobacterium avium subsp paratuberculosis (MAP) or from which MAP was isolated from feces with those for cows that were seronegative for antibodies against or culture negative for MAR Design--Retrospective study. Animals--4,842 beef cows from 3 herds enrolled in the USDA National Johne's Disease Demonstration Herd Project. Procedures--Individual cow ELISA and culture results were obtained from the project database. During each parity evaluated for each cow, the 205-day adjusted weaning weight (AWW) of its calf was calculated. The AWW was compared between test-positive and test-negative cows by use of multilevel mixed-effect models. The median value for feeder calves from 2007 to 2011 was used to estimate the economic losses associated with MAP test-positive cows. Results--The AWW of calves from cows with strongly positive ELISA results was 21.48 kg (47.26 lb) less than that of calves from cows with negative ELISA results. The AWW of calves from cows classified as heavy or moderate MAP shedders was 58.51 kg (128.72 lb) and 40.81 kg (89.78 lb) less, respectively, than that of calves from MAP culture-negative cows. Associated economic losses were estimated as $57.49/calf for cows with strongly positive ELISA results and $156.60/calf and $109.23/calf for cows classified as heavy and moderate MAP shedders, respectively. Conclusions and Clinical Relevance--Calves from cows with MAP-positive test results had significantly lower AWWs than did calves from cows with MAP-negative test results, which translat-ed into economic losses for MAP-infected beef herds. [ABSTRACT FROM AUTHOR]

Abstract: One thousand three hundred and twenty-four adult beef cattle were tested for paratuberculosis using 2 antibody enzyme-linked immunosorbent assays (ELISA), an interferon-gamma (INF-γ) ELISA, and radiometric bacterial culture of feces from 5 populations. Two populations of cattle (n =226) had data available to calculate a ratio of humoral to cell-mediated immunity based on results from one antibody test and the INF-γ ELISA. Latent class analysis was used to estimate accuracy of the 4 paratuberculosis assays within a Bayesian framework. Determination of test accuracy and paratuberculosis prevalence in the latent class analysis allowed for estimation of predictive value positive (PVP) functions. The estimated PVP functions were used to iteratively assign paratuberculosis status to sampled cattle. Accuracy of the immunity ratio, an antibody ELISA, and the INF-γ ELISA were determined for multiple cutoffs based on probabilistically assigned paratuberculosis status. Area under the receiver-operating characteristic (ROC) curves (95% probability interval) were estimated as 0.78 (0.66, 0.89), 0.81 (0.68, 0.92), and 0.59 (0.47, 0.71) for the immunity ratio, antibody ELISA, and INF-γ ELISA, respectively. The Youden index (sensitivity+specificity−1) peaked at immunity ratios of 0.5 (J =0.48) and 1.0 (J =0.46). Sensitivity and specificity (95% probability interval) at an immunity ratio cutoff of 0.5 were 0.65 (0.44, 0.85) and 0.83 (0.78, 0.88), respectively. Sensitivity and specificity (95% probability interval) at the 1.0 cutoff were 0.55 (0.33, 0.77) and 0.91 (0.87, 0.95), respectively. An immunity ratio could be used to diagnosis paratuberculosis in beef cattle but requires further investigation. [Copyright &y& Elsevier]

Dogs are the only non-equid species to develop the fatal form of African horse sickness (AHS). Research conducted in 2013 questioned the long-held belief that naturally occurring cases of AHS in dogs were contracted exclusively through the ingestion of contaminated horse meat. Culicoides midges, the vector of AHS virus (AHSV) for horses, have an aversion to dog blood meals and dogs were believed to be dead-end or incidental hosts. More recently, dog mortalities have occurred in the absence of horse meat consumption and vector transmission has been suspected. The current study is a retrospective serological survey of AHSV exposure in dogs from an endemic area. Dog sera collected from dogs (n = 366) living in the city of Tshwane, Gauteng Province, South Africa, were randomly selected from a biobank at a veterinary teaching hospital , corresponding to the years 2014–2019. The study used a laboratory in-house indirect recombinant VP7 antigen-based enzyme-linked immunosorbent assay (iELISA) with a test cut-off calculated from AHSV exposure-free dog sera (n = 32). Study AHSV seroprevalence was 6 % (22/366) with an estimated true prevalence of 4.1 % (95 % confidence interval (CI) = 1.3–8.1 %). Incidence was estimated for dogs with multiple serological results with seroconversion occurring at a rate of 2.3 seroconversions per 10 dog years at risk (95 % CI = 0.6–6.2). A subsection of the study sera was tested with AHSV viral neutralisation test (VN) (n = 42) for serotype determination. Antibodies to AHSV serotype 6 were most prevalent (90 %) in VN seropositive dogs (n = 20) with most dogs seemingly subclinically infected (>95 %). Seroprevalence descriptively varied by year and identified risk factors were annual rainfall > 754 mm (odds ratio (OR) = 5.76; 95 % CI = 2.22 – 14.95; p < 0.001), medium human population densities, 783–1663 people/km2 (OR = 7.14; 95 % CI = 1.39 – 36.73; p = 0.019) and 1664–2029 people/km2 (OR = 6.74; 95 % CI = 1.40 – 32.56; p = 0.018), and the month of March (OR = 5.12; 95 % CI = 1.41 – 18.61; p = 0.013). All identified risk factors were consistent with midge-borne transmission to dogs. The relatively high seroprevalence and seroconversion rates suggest frequent exposure of dogs to AHSV and indicates the need to investigate the role dogs might play in the overall epidemiology and transmission of AHSV. [ABSTRACT FROM AUTHOR]