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1.
The study objective was to evaluate the accuracy of a real-time polymerase chain reaction (RT-PCR) and a culture protocol used to detect Salmonella in the faeces of grow-finish pigs using a Bayesian approach. The RT-PCR was invA-gene-based assay, while the culture protocol included pre-enrichment in buffered peptone water, selective enrichment in tetrathionate and Rappaport-Vassiliadis broths, and isolation on semi-solid (modified semi-solid RV) or solid (XLT4, Rambach) agar plates. Bayesian analysis was performed using a two-test, two-population model with dependence between culture and RT-PCR and compared to a second model with conditional independence between these two tests. Two hundred and ninety three individual faecal and 294 pooled pen samples from grow-finish pig collected from 10 farms were tested and results were divided into two groups according to herd size (five herds <250 sows, five herds with >400 sows). In the dependence model, RT-PCR sensitivity (Se) and specificity (Sp) were estimated to be 90% (95% probability interval 74, 97) and 99% (98, 99), respectively. Culture Se was 92% (75, 99), while culture Sp was considered 100% as all culture-positive samples were confirmed by serotyping. In the conditional independence model, RT-PCR Se and Sp, and culture Se, were 96% (93, 98), 99% (98, 100) and 97% (94, 100), respectively. The dependence model resulted in posterior estimates of Se that were lower and with broader probability intervals than the independence model, indicating that when RT-PCR and culture are evaluated relative to each other, the correlation between these tests is an important source of bias and should be adjusted for during analysis. The RT-PCR evaluated in this study performed almost comparably to culture; given the cost savings associated with using this test and more timely results, the RT-PCR may be a useful alternative to culture for screening large numbers of samples, particularly when Salmonella prevalence is low.  相似文献   

2.
The purposes of this study were to describe the clinical signs observed in PRRS positive herds during a porcine reproductive and respiratory syndrome (PRRS) outbreak in Ontario and to determine associations between these clinical signs and herd demographics and PRRS control strategies. All PRRS polymerase chain reaction-(PCR)-positive submissions to a diagnostic laboratory between September 1, 2004 and August 31, 2007 were identified (n = 1864). After meeting eligibility requirements and agreeing to voluntary study participation, producers from 455 of these submissions were surveyed for information on clinical signs observed in their herds, herd demographics, and PRRS control strategies used in their herds at the time that the PCR-positive samples were taken. Larger herd size was associated with an increased risk of reporting abortion, weakborn piglets, off-feed sows, and sow mortality in sow herds, and with an increased risk of reporting mortality in finishing herds. When disease control strategies were examined, use of a commercial PRRS vaccine in sows and gilts was associated with a decreased risk of reporting weakborn pigs and high pre-weaning mortality, while the use of serum inoculation in breeding animals was associated with an increased risk of reporting off-feed sows and sow mortality. Providing biofeedback of stillborn/mummified piglets, placenta or feces to gilts was associated with an increased risk of reporting respiratory disease and mortality in finishing pigs while all-in/all-out flow in farrowing rooms was associated with an increased risk of reporting sow mortality and weakborn piglets.  相似文献   

3.
An indirect ELISA test was developed as a novel tool aimed at monitoring the herd infection status of swine herds. Meat juice samples from pig carcasses were analysed for the presence of antibodies against porcine reproductive and respiratory syndrome virus (PRRSV). A study of samples from herds with known PRRS status was undertaken. The PRRS status of the herds was evaluated based on the analysis of blood samples by another serological test (blocking ELISA) capable of differentiating between infection with PRRSV of the American type and European type. The specificity of the indirect ELISA test on meat juice samples was 0.98. The sensitivity of the test depended on the type of the PRRSV strain involved. The apparent prevalence in herds infected with the American type of PRRSV was 0.44. The apparent prevalence in herds infected with the European type of PRRSV was 0.64. Herd level sampling and herd level criteria for assessing the PRRS status of herds by the new test were developed. Herds were classified as PRRS negative or PRRS seropositive based on 10 meat juice samples collected randomly at slaughter throughout a 3-month-period. Herd PRRS status classification by the indirect ELISA was validated in 47 herds by collection of blood samples from the herds. Eighteen herds were classified as PRRS negative by both test systems. Twenty-nine herds were classified as PRRS seropositive by both test systems. Acceptable herd classification was achieved using this test.  相似文献   

4.
A survey of blood selenium (Se) concentrations in Norwegian Red heifers and dry period cows was conducted to reveal possible association to management, feeding, health and fertility. Selenium contents were determined in 254 herd blood samples consisting of pooled samples from individual non-lactating animals from herds in 5 counties. The Se concentrations showed a normal distribution with mean 0.09 microg Se/g blood, with a standard deviation (SD) of 0.05, and ranged from 0.02 to 0.23 microg/g, with 50 % of the samples being between 0.06 and 0.11 microg/g. The herds with Se concentrations below 0.06 microg/g were smaller (21.4 +/- 8.7 cow-years) than those with Se levels above 0.11 microg/g (27.5 +/- 14.1 cow-years) (P<0.01), but there were no differences in milk yield, incidence of replacement, proportion of animal culling, amount of concentrate or grass silage as percentage of energy consumption between the groups. Treatment registration records showed a tendency that more animals in the low Se herds were treated for all the diseases included in this investigation (64.8 animals per 100 cow-years) than those in the high Se herds (57.5 per 100 cow-years), while no such differences were revealed for individual disorders. There was, however, a significant difference in bulk milk somatic cell counts (BMSCC) between low and high Se herds, their values being 137 000 and 155 000 cells/ml, respectively. This difference was significantly influenced by herd size. Furthermore, a total of 4916 lactations were analyzed from individual health and fertility recordings, including 2 934 first lactations and 1 982 later lactations. The present study revealed a reduced incidence of disease treatment with increased Se concentrations from 0.02 to 0.23 microg Se/g blood. In this regard, there seemed to be an optimum of 0.10 to 0.15 microg Se/g for all types of mastitis treatments summarized, and for treatment of retained placenta. Thus, herd Se concentrations below and above these values was connected with increased probability for sum mastitis and retained placenta, reflecting the effect of the quadratic term of Se. The cow (composite) milk somatic cell count (SCC) was lower in lactations from low Se herds than in high Se herds with a marked SCC increase in the Se concentration interval from 0.11-0.13 microg/g blood. In conclusion, heifers and dry period cows in Norway are low in blood Se content and there seems to be a positive association between increased blood Se concentration pre partum and decreased incidence of mastitis, ovarian cysts and anoestrus/silent oestrus post partum.  相似文献   

5.
A simple random survey was conducted in Ireland during 2005 to estimate the ELISA-prevalence of paratuberculosis, commonly called Johne's disease (JD), in the cattle population. Serum samples were collected from all 20,322 females/breeding bulls over 12 months-of-age in 639 herds. All samples were tested using a commercially available absorbed ELISA. The overall prevalence of infected herds, based on the presence of at least one ELISA-positive animal, was 21.4% (95% CI 18.4%-24.9%). Herd prevalence levels amongst dairy herds (mean 31.5%; 95% CI: 24.6%, 39.3%) was higher than among beef herds (mean 17.9%; 95% CI: 14.6%-21.8%). However, the animal level prevalence was similar. The true prevalence among all animals tested, was calculated to be 2.86% (95%CI: 2.76, 2.97) and for animals >= 2 yrs, it was 3.30% (95%CI: 3.17, 3.43). For animals in beef herds, true prevalence was 3.09% (95%CI: 2.93, 3.24), and for those in dairy herds, 2.74% (95%CI: 2.59, 2.90). The majority of herds had only one ELISA-positive infected animal. Only 6.4% (95% CI 4.7%-8.7%) of all herds had more than one ELISA-positive infected animal; 13.3% (CI 8.7%-19.7%) of dairy herds ranging from two to eight ELISA-positive infected animals; and, 3.9% beef herds (CI 2.4%-6.2%) ranging from two to five ELISA-positive infected animals. The true prevalence of herds infected and shedding Mycobacterium avium subspecies paratuberculosis is estimated to be 9.5% for all herd types; 20.6% for dairy herds; and 7.6% for beef herds. If ELISA positive animals <2-years-of-age are excluded, the true herd prevalene reduces to: 9.3% for all herd types; 19.6% for dairy herds; and 6.3% for beef herds based on a test specificity (Sp) of 99.8% and test sensitivity (Se) (i.e., ability to detect culture-positive, infected animals shedding at any level) of 27.8-28.9%.  相似文献   

6.
We report the results of the first survey for antibody against bluetongue virus (BTV) that was conducted in Switzerland in the year 2003. In a nationwide cross-sectional study with partial verification, 2437 cattle sera collected from 507 herds were analysed using competitive enzyme-linked immunosorbent assays (c-ELISA). To adjust for misclassification, 158 sera, including 86 that were recorded equivocal in Switzerland, were sent to the Office Internationale des Epizooties designated regional reference laboratory in the UK for confirmation. No BTV antibody was detected in any of these samples, confirming the absence of BTV from Switzerland in 2003. The specificity of the c-ELISA used in Switzerland for individual Swiss cattle was calculated to be 96.5%. The mean herd sensitivity achieved in our survey ranged from 78.9% to 98.8% depending on the with-in herd prevalence and test sensitivity used for the calculations. The cumulated confidence level achieved with the survey based on a minimal expected prevalence of 2%, was 99.99% and therefore it was concluded that there was no evidence of BTV circulation in Switzerland in 2003.  相似文献   

7.
Rikula U  Nuotio L  Aaltonen T  Ruoho O 《Preventive veterinary medicine》2005,72(1-2):139-42; discussion 215-9
The bovine viral diarrhoea virus (BVDV) situation among dairy herds and suckler-cow herds was monitored annually from 1998 to 2004. Bulk-tank milk (BTM) samples from all dairy herds and serum samples from beef animals at slaughter were examined for BVDV antibodies using a commercial indirect ELISA test. New BTM antibody-positive herds and herds with a history of BTM antibodies, but previously untested were sampled individually and tested for evidence of BVDV. The reason for the antibody-positivity or the source of infection was investigated. The percentage of BTM antibody-positive herds ranged from 0.45% in 2000 to 0.15% in 2003. The number of herds with persistently infected (PI) animals ranged from 10 in 2001 to 0 in 2003. The most common cause for a herd to become BTM antibody-positive was the purchase of a seropositive animal or a PI animal or a dam carrying a PI fetus. The new BVD decree of 2004 will be described in brief.  相似文献   

8.
In July 2007, PRRS was detected for the first time in Sweden. A total of eight positive herds were identified and various measures were taken to eradicate the disease, including restrictions and slaughter of infected herds. Subsequently, both active and passive surveillance activities were undertaken. This study describes stochastic scenario-tree modelling of all the various surveillance system components, to estimate the current probability that Sweden is free from PRRS. The model includes all actions taken after the first positive herd was detected. The surveillance system components included in the model were as follows: investigations undertaken in association with the outbreak, a serological study based on samples collected at slaughter, samples collected in the national PRRS surveillance programme and passive clinical surveillance. The probability of freedom was estimated in time steps of 1 month, from July to December 2007. After each time step, the calculated posterior probability of freedom from the previous month, combined with the probability of introduction, was used as a prior probability for the next month.The result from the model showed a 99.8% probability that Sweden was free from PRRS at the end of December 2007. The estimated total sensitivity of the surveillance system varied between 81.2% and 94.3% and was highest during the first months after the outbreak. For sensitivity analysis purposes, the model was also applied using higher risks of introduction. However, this did not make considerable difference to the final estimates.  相似文献   

9.
Our objective was to determine the seroprevalence of Hypoderma spp. and to develop a spatial model describing the risk surface of warble-fly infection in Belgian cattle herds (adjusting for herd size, herd type, local temperature, rainfall, relative air humidity and land-cover). This survey was carried out in 390 selected herds of all types (dairy, mixed and beef) from December 1997 to March 1998, which were included in a national infectious bovine rhinotracheitis and paratuberculosis (Johne's-disease) survey. All animals >24 months old were blood sampled and an ELISA was used on pooled serum samples (10 animals per pool). The herd seroprevalence was 48.7% (95% confidence interval: 43.6-53.8); positive herds were mainly in the south of the country and along the North Sea coast. The logistic multiple-regression model of herd-level seropositivity indicated that mixed-type and beef-cattle herds have more than four-fold and two-fold increases in the odds of being Hypoderma-positive, respectively, compared with dairy herds.  相似文献   

10.

Background

Staphylococcus aureus is one of the most common causes of intramammary infections in dairy cows at dry off. Reliable identification is important for disease management on herd level and for antimicrobial treatment of infected animals. Our objective was to evaluate the test characteristics of PathoProof ™ Mastitis PCR Assay and bacteriological culture (BC) in diagnosing bovine intramammary infections caused by S. aureus at dry off at different PCR cycle threshold (Ct)-value cut-offs.

Methods

Sterile quarter samples and non-sterile composite samples from 140 animals in seven herds were collected in connection with the dairy herd improvement (DHI) milk recording. All quarter samples were analyzed using BC whereas all composite samples were analyzed with PathoProof ™ Mastitis PCR Assay. Latent class analysis was used to estimate test properties for PCR and BC in the absence of a perfect reference test. The population was divided into two geographically divided subpopulations and the Hui-Walter 2-test 2-populations model applied to estimate Se, Sp for the two tests, and prevalence for the two subpopulations.

Results

The Se for PCR increased with increasing Ct-value cut-off, accompanied by a small decrease in Sp. For BC the Se decreased and Sp increased with increasing Ct-value cut-off. Most optimal test estimates for the real-time PCR assay were at a Ct-value cut-off of 37; 0.93 [95% posterior probability interval (PPI) 0.60-0.99] for Se and 0.95 [95% PPI 0.95-0.99] for Sp. At the same Ct-value cut-off, Se and Sp for BC were 0.83 [95% PPI 0.66-0.99] and 0.97 [95% PPI 0.91-0.99] respectively. Depending on the chosen PCR Ct-value cut-off, the prevalence in the subpopulations varied; the prevalence increased with increasing PCR Ct-value cut-offs.

Conclusion

Neither BC nor real-time PCR is a perfect test in detecting IMI in dairy cows at dry off. The changes in sensitivity and prevalence at different Ct-value cut-offs for both PCR and BC may indicate a change in the underlying disease definition. At low PCR Ct-value cut-offs the underlying disease definition may be a truly/heavily infected cow, whereas at higher PCR Ct-value cut-offs the disease definition may be a S. aureus positive cow.  相似文献   

11.
  相似文献   

12.
Streptococcus agalactiae mastitis persists as a significant economic problem for the dairy industry in many countries. In Denmark, the annual surveillance programme for this mastitis pathogen initially based only on bacteriological culture of bulk tank milk (BTM) samples, has recently incorporated the use of the real-time PathoProof Mastitis PCR assay with the goal of improving detection of infected herds. The objective of our study was to estimate the herd sensitivity (Se) and specificity (Sp) of both tests of BTM samples using latent class models in a Bayesian analysis while evaluating the effect of herd-level covariates on the Se and Sp of the tests. BTM samples were collected from all 4258 Danish dairy herds in 2009 and screened for the presence of S. agalactiae using both tests. The highest Se of PCR was realized at a cycle threshold (Ct) cut-off value of 40. At this cut-off, the Se of the PCR was significantly higher (95.2; 95% posterior credibility interval [PCI] [88.2; 99.8]) than that of bacteriological culture (68.0; 95% PCI [55.1; 90.0]). However, culture had higher Sp (99.7; 95% PCI [99.3; 100.0]) compared to PCR (98.8; 95% PCI [97.2; 99.9]). The accuracy of the tests was unaffected by the herd-level covariates. We propose that screenings of BTM samples for S. agalactiae be based on the PCR assay with Ct readings of <40 considered as positive. However, for higher Ct values, confirmation of PCR test positive herds by bacteriological culture is advisable especially when the between-herd prevalence of S. agalactiae is low.  相似文献   

13.
The precalen-ce of caseous lymphadenitis was surveyed in 36 goat herds in Northern Norway. In each herd, information concerning the occurrence of the disease was obtained from the farmer. Adult animals (1 year of age or older) in 35 herds were examined for superficial swellings, and serum samples were collected from most animals in the herds. The sera were examined for antibodies to Corynebacterium pseudotuber-culosis using the bacterial agglutination test (BAT) and the hemolysis inhibition test (HIT).Gaseous lymphadenitis was diagnosed with certainty in 19 herds. Information from the farmers indicated that the disease indeed oc-curred in these herds, and that the majority had been infected with the disease for many years. The herds had apparently become infected through contact with animals from infected herds. Clinical examina-tions were carried out in 18 of these herds and superficial swellings were found in 26 % of the examined animals. The prevalence of ani-mals with lesions varied from 11 to 40 % among the herds. Of the animals in these herds, 81 % were positive in BAT and 84 % in HIT. The prevalence of positive animals varied from 26 to 99 % in BAT and 28 to 99 % in HIT. The prevalence of seropositive animals was lowest in a herd in which animals were kept separately in stalls.Caseous lymphadenitis could not be diagnosed in 16 herds. In-formation from the farmers indicated that the disease indeed seemed to be absent in 14 of these herds. These 14 herds had no history of contact with animals from herds considered to be infected. However, in the remaining 2 herds, the farmers were somewhat uncertain about the occurrence of the disease. One of these 2 herds had a history of contact with infected herds through participation in a goat “breeding circle”. Only a few of the animals were, however, seropositive and all these had low antibody titres.In 1 newly established herd, a single animal showed a high posi-tive titre in BAT only. All the other animals were negative in both tests. This particular herd consisted of animals obtained both from herds with caseous lymphadenitis and from herds in which the disease was not considered to occur.  相似文献   

14.
The national bovine paratuberculosis (PTB) seroprevalence (apparent prevalence) in the Belgian cattle population was determined by a serological survey that was conducted from December 1997 to March 1998. In a random sample of herds (N=556, 9.5%), all adult cattle of 24 months of age or older (N=13,317, 0.4%) were tested for the presence of antibodies using a commercially available absorbed ELISA test kit. The PTB median within-herd seroprevalence (proportion of detected animals within the seropositive herds) and the PTB individual-animal seroprevalence (proportion of detected animals) were, respectively, 2.9% (quartiles=1.6-5.6) and 0.87% (95% confidence interval (CI)=0.71-1.03). The PTB herd seroprevalence (proportion of detected herds) was 18% (95% CI=14-21).Assuming a test sensitivity and specificity of 45 and 99% [Sweeney et al., 1995. J. Vet. Diagn. Invest. 7 (4), 488; Sockett et al., 1992. J. Clin. Microbiol. 30 (5), 1134], respectively, the median true within-herd prevalence and the true individual-animal were estimated to be 7 and 2%, respectively. The true herd prevalence of Mycobacterium paratuberculosis infection was first estimated according to currently accepted methodology. This calculation revealed that the specificity of the used test has a dramatic effect on the estimation; assuming a test sensitivity of 45% and a true within-herd prevalence of 7%, the true herd prevalence estimation decreased from 36 to 0.8% if the test specificity decreased from 99. 9 to 99%, respectively. This sensitivity analysis showed that the practical limits of the accuracy of the used screening test jeopardize the estimation of the true herd prevalence within reasonable confidence limits, because the within-herd PTB true prevalence was low.For this reason we augmented the herd specificity for herds with larger adult herd size (>5). This was done by increasing the cut-off number of positive cattle required (>/=2) to classify a herd truly positive and including herds with one positive test result if there was historical evidence of PTB (previous diagnosis and/or clinical signs). This approach resulted in an estimated true herd prevalence of M. paratuberculosis infection of 6%. The true herd prevalence for dairy, mixed and beef herds was, respectively, 10, 11 and 3%.  相似文献   

15.
Knowledge of the sensitivity of diagnostic tests for infectious diseases under field conditions can be used to design a surveillance program that increases the effectiveness of the control policy. In this study, the sensitivity of tests for the detection of classical swine fever (CSF) virus (CSFV) under field conditions was estimated without knowledge of the true disease status of the animals tested. During the CSF epidemic of 1997-1998 in The Netherlands, tonsil samples from pigs of CSF suspect farms were collected for laboratory diagnosis of CSE These specimens were tested in a fluorescence antibody test (FAT1) for the presence of CSFV antigen. When at least 1 specimen in a particular sample series from a farm was positive, this farm was declared CSFV infected. Specimens of that series, either FAT1 negative (98) or FAT1 positive (127), were subsequently tested again (FAT2). After that, a suspension was made of the remaining tissue, and this suspension was evaluated with a virus isolation test. In total, 225 tonsil specimens were examined. A statistical model was formulated, and the sensitivity of the 3 tests and the prevalence of positive specimens in the sample were estimated by the method of maximum likelihood. The sensitivity of the FAT1, the test that was used for confirmation of CSFV infection in a pig herd, was approximately 78% (95% confidence interval [CI] = 62-92%). The effectiveness of the selection process of animals on the farm by the veterinarian was estimated to be 77% (64-87%). The sensitivity of the combination of FAT1 and FAT2 (60%) indicates that at least 5 animals should be selected on a CSF-suspect farm to gain a detection probability for CSFV of 99%.  相似文献   

16.
OBJECTIVE: To examine piggeries in Queensland for evidence of infection with Hendra virus and Nipah virus. DESIGN: A serological survey was designed to provide 99% confidence of detecting at least one infected pig herd in Queensland, assuming that for each virus, at least 5% of herds would have been exposed to virus and that at least 40% of the finisher pigs in these herds would have detectable antibodies to virus. PROCEDURE: A two stage sampling regimen was used. All samples were tested with serum neutralisation tests developed and performed at the Australian Animal Health Laboratory. RESULTS: There was no evidence of antibody to either virus in the 500 samples collected from 100 herds. CONCLUSION: The results of the survey support a case that commercial pigs in Queensland are free of both Hendra virus and Nipah virus infections.  相似文献   

17.
A stochastic spreadsheet model was developed to obtain estimates of the costs of whole herd testing on dairy farms for Mycobacterium avium subsp. paratuberculosis (Map) with pooled fecal samples. The optimal pool size was investigated for 2 scenarios, prevalence (a low-prevalence herd [< or = 5%] and a high-prevalence herd [> 5%]) and for different herd sizes (100-, 250-, 500- and 1,000-cow herds). All adult animals in the herd were sampled, and the samples of the individuals were divided into equal sized pools. When a pool tested positive, the manure samples of the animals in the pool were tested individually. The individual samples from a negative pool were assumed negative and not tested individually. Distributions were used to model the uncertainty about the sensitivity of the fecal culture at farm level and Map prevalence. The model randomly allocated a disease status to the cows (not shedding, low Map shedder, moderate Map shedder, and heavy Map shedder) on the basis of the expected prevalence in the herd. Pooling was not efficient in 100-cow and 250-cow herds with low prevalence because the probability to detect a map infection in these herds became poor (53% and 88%) when samples were pooled. When samples were pooled in larger herds, the probability to detect at least 1 (moderate to heavy) shedder was > 90%. The cost reduction as a result of pooling varied from 43% in a 100-cow herd with a high prevalence to 71% in a 1,000-cow herd with a low prevalence. The optimal pool size increased with increasing herd size and varied from 3 for a 500-cow herd with a low prevalence to 5 for a 1,000-cow herd with a high prevalence.  相似文献   

18.
OBJECTIVE: To describe the distribution and prevalence of cattle herds with detectable antibody to bovine pestivirus in Queensland in 1994/95. MATERIALS AND METHODS: The study used 7,838 serum samples collected from 250 herds in Queensland, as part of a structured animal health surveillance program conducted in 1994 and 1995. Samples were collected from female cattle bred on the property. In each herd, 10 to 20 heifers less than two years of age and 10 to 15 older cows were sampled giving a 95% probability of detecting one or more seropositive animals if the seroprevalence was approximately 10% or greater. Sera were analysed for antibodies to bovine pestivirus using a virus neutralisation test. RESULTS: Total cattle numbers in sampled herds varied from 62 to 24,600 head, while total area of properties sampled varied from 50 to 395,400 hectares. Eleven percent of herds contained no seropositive animals among those sampled, and in 38% of herds, all sampled cattle aged one to two years of age were seronegative. There was a trend for larger herds to have one or more animals seropositive for bovine pestivirus (chi-squared for Linear trend = 3.656, p = 0.056). Herds with more than 500 head of cattle were significantly more likely than herds with less than 500 head to contain one or more seropositive animals in any age group (prevalence ratio = 1.12; 95% confidence interval 1.01 - 1.23; p = 0.026). Age specific seroprevalence increased from around 10% in heifers, to between 75% and 85% in cows aged 10 years. The average annual incidence risk for bovine pestivirus infection varied from 0.12 to 0.24 seroconversions per cattle year at risk, and did not vary with age. The overall crude seroprevalence adjusted for herd size was 45%. There was a wide range of seroprevalence recorded for each level of stocking intensity. CONCLUSIONS: This survey provides valuable baseline data on bovine pestivirus infection in Queensland cattle herds.  相似文献   

19.
AIMS: To determine the sensitivity (Se) and specificity (Sp) of pregnancy diagnosis using transrectal ultrasonography and an ELISA for pregnancy-associated glycoprotein (PAG) in milk, in lactating dairy cows in seasonally calving herds approximately 85–100 days after the start of the herd’s breeding period.

METHODS: Paired results were used from pregnancy diagnosis using transrectal ultrasonography and ELISA for PAG in milk carried out approximately 85 and 100 days after the start of the breeding period, respectively, from 879 cows from four herds in Victoria, Australia. A Bayesian latent class model was used to estimate the proportion of cows pregnant, the Se and Sp of each test, and covariances between test results in pregnant and non-pregnant cows. Prior probability estimates were defined using beta distributions for the expected proportion of cows pregnant, Se and Sp for each test, and covariances between tests. Markov Chain Monte Carlo iterations identified posterior distributions for each of the unknown variables. Posterior distributions for each parameter were described using medians and 95% probability (i.e. credible) intervals (PrI). The posterior median estimates for Se and Sp for each test were used to estimate positive predictive and negative predictive values across a range of pregnancy proportions.

RESULTS: The estimate for proportion pregnant was 0.524 (95% PrI?=?0.485–0.562). For pregnancy diagnosis using transrectal ultrasonography, Se and Sp were 0.939 (95% PrI?=?0.890–0.974) and 0.943 (95% PrI?=?0.885–0.984), respectively; for ELISA, Se and Sp were 0.963 (95% PrI?=?0.919–0.990) and 0.870 (95% PrI?=?0.806–0.931), respectively. The estimated covariance between test results was 0.033 (95% PrI?=?0.008–0.046) and 0.035 (95% PrI?=?0.018–0.078) for pregnant and non-pregnant cows, respectively. Pregnancy diagnosis results using transrectal ultrasonography had a higher positive predictive value but lower negative predictive value than results from the ELISA across the range of pregnancy proportions assessed.

CONCLUSIONS AND CLINICAL RELEVANCE: Pregnancy diagnosis using transrectal ultrasonography and ELISA for PAG in milk had similar Se but differed in predictive values. Pregnancy diagnosis in seasonally calving herds around 85–100 days after the start of the breeding period using the ELISA is expected to result in a higher negative predictive value but lower positive predictive value than pregnancy diagnosis using transrectal ultrasonography. Thus, with the ELISA, a higher proportion of the cows with negative results will be non-pregnant, relative to results from transrectal ultrasonography, but a lower proportion of cows with positive results will be pregnant.  相似文献   

20.
Objective To provide serological data to support Australia's claim of freedom from porcine reproductive and respiratory syndrome.
Design A national serological survey was designed to provide 99% confidence of detecting at least one infected pig herd in Australia, assuming that at least 5% of herds would have been exposed to porcine reproductive and respiratory syndrome virus and that at least 25% of the 'finisher' pigs in these herds would have antibodies to the virus.
Procedure A two-stage testing regime was used. All samples were tested with a commercially available enzyme-linked immunosorbent assay. If assay reactions were found, all samples from the herd were to be tested using the indirect immunofluorescence antibody assay.
Results Of the 875 samples from 163 herds from all States in Australia, there was some evidence of reactivity in only four samples from four herds on the enzyme-linked immunosorbent assay. Further testing using the indirect immunofluorescence antibody assay according to the study protocol demonstrated that the reactions were not due to the presence of specific porcine reproductive and respiratory syndrome virus antibodies in the sera.
Conclusion The results of this study support the view that Australian pigs are free of porcine reproductive and respiratory syndrome virus.  相似文献   

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