Assessment of the specificity of a gamma-interferon test performed with specific antigens to detect bovine tuberculosis, after non-negative results to intradermal tuberculin testing.

In cattle herds in France, cervical skin tests (STs) using simple intradermal tuberculin (SIT) are performed to detect bovine tuberculosis (bTB). When positive results are found on ST screening, the herd is considered to be 'under suspicion' and confined, raising economic issues. The suspicion can be lifted by carrying out a single intradermal cervical comparative test (SICCT) at least six weeks later. The authors conducted an experimental study in France between 2013 and 2015 to assess the accuracy of the gamma-interferon test (IFN-γ), used in series after a non-negative result to ST screening, and to study the possibility of replacing the SICCT performed six weeks later by an IFN performed within a few days. Data were collected concerning 40 infected and 1825 bTB-free animals from herds with non-negative results to ST screening. This study showed that the IFN-γ test based on specific antigens and performed within a few days of a non-negative result to the ST has higher sensitivity than the SICCT performed six weeks later and equal specificity. The IFN test is more convenient to perform; however, it is more expensive. The IFN-γ test based on MIX antigens may be a useful alternative to the SICCT, to shorten the confinement period of suspect herds without underdetecting bTB.

The importance of communication in promoting voluntary participation in an experimental trial: A qualitative study based on the assessment of the gamma-interferon test for the diagnosis of bovine tuberculosis in France.

Understanding the factors leading each stakeholder to participate in an experimental trial is a key element for improving trial set-up and for identifying selection bias in statistical analyses. An experimental protocol, validated by the European Commission, was developed in France to assess the ability of the gamma-interferon test in terms of accuracy to replace the second intradermal skin test in cases of suspected bovine tuberculosis. Implemented between 2013 and 2015, this experimental trial was based on voluntary participation. To determine and understand the motivation or reluctance of farmers to take part in this trial, we carried out a sociological survey in France. Our study was based on semi-structured interviews with the farmers and other stakeholders involved. The analysis of findings demonstrated that shortening the lock-up period during tuberculosis suspicion, following the use of a gamma-interferon test, was an important aim and a genuine challenge for the animal health stakeholders. However, some farmers did not wish to continue the trial because it could potentially have drastic consequences for them. Moreover, misunderstandings and confusion concerning the objectives and consequences of the trial led stakeholders to reject it forcefully. Based on our results, we offer some recommendations: clear and appropriate communication tools should be prepared to explain the protocol and its aims. In addition, these types of animal health trials should be designed with the stakeholders' interests in mind. This study provides a better understanding of farmer motivations and stakeholder influences on trial participation and outcomes. The findings can be used to help design trials so that they promote participation by farmers and by all animal health stakeholders in general.

Effects of management practices as risk factors for juvenile osteochondral conditions in 259 French yearlings.

Several studies have demonstrated a statistical association between management practices and juvenile osteochondral conditions (JOCC) in foals from birth to 6months of age, but this association has not been investigated in yearlings. The purpose of the current study was to determine the adjusted effects of management practices on the onset and evolution of JOCC in French yearlings. The study sample consisted of 259 yearlings born on 20 stud farms in Normandy. The breeding conditions of these horses were monitored from 6 to 17months. They were radiographed at 6 and 17months to determine their radiographic score (RS) and its evolution. Potential risk factors were investigated using univariate and multivariate analyses. The prevalence of JOCC was 48% at 6months and 42% at 17months. Between 6 and 17months, the RS changed (for better or worse) in 52% of yearlings. The main risk factors leading to deterioration in the RS were traumatic. 'Mixed housing' during winter, pastures with rough ground and a bad RS at 6months were significantly associated with deterioration in RS between 6 and 17months. In the multivariate analysis, the breed was not significantly associated with any evolution in the yearlings' RS. This study provides some indications on protective measures to prevent the worsening of JOCC lesions between 6 and 17months, a crucial period since it precedes the sale of yearlings and the beginning of training.

Evaluation of five serological tests for the diagnosis of porcine brucellosis in French Polynesia.

Porcine brucellosis due to Brucella suis biovar 1 raises important issues for pig breeders in French Polynesia. In this region, the disease is enzootic, spreads silently and engenders economic losses in infected farms as well as sporadic human cases. While serological tests are essential in surveillance and control programmes of animal diseases, to date none of the available tests have been shown to be reliable enough to be used as a gold standard in routine individual diagnosis of porcine brucellosis. Few studies about the estimation of the sensitivity and the specificity of porcine brucellosis screening tests have been published, none of them dealing with French Polynesia. The studied population included 1,595 pigs from French Polynesia. Five tests were evaluated: Rose Bengal test, fluorescence polarisation assay, indirect ELISA, and two competitive ELISAs (C-ELISA). The sensitivity and the specificity of each test were estimated. C-ELISA2 was the most sensitive test (Se C-ELISA2=0.954 [0.889; 0.992] 95% credibility interval (CrI)) while both C-ELISA and Rose Bengal test (RBT) were the most specific ones (Sp C-ELISA1=0.856 [0.806; 0.915] 95% CrI; Sp C-ELISA2=0.849 [0.817; 0.879] 95% CrI; Sp RBT=0.853 [0.812; 0.898] 95% CrI).

Assessment of the diagnostic sensitivity and specificity of an indirect ELISA kit for the diagnosis of Brucella ovis infection in rams.

BACKGROUND: Brucella ovis causes an infectious disease responsible for infertility and subsequent economic losses in sheep production. The standard serological test to detect B. ovis infection in rams is the complement fixation test (CFT), which has imperfect sensitivity and specificity in addition to technical drawbacks. Other available tests include the indirect enzyme-linked immunosorbent assays (I-ELISA) but no I-ELISA kit has been fully evaluated.The study aimed to compare an I-ELISA kit and the standard CFT. Our study was carried out on serum samples from 4599 rams from the South of France where the disease is enzootic. A Bayesian approach was used to estimate tests characteristics (diagnostic sensitivity, Se and diagnostic specificity, Sp). The tests were then studied together in order to optimise testing strategies to detect B. ovis. RESULTS: After optimising the cut-off values in order to avoid doubtful results without deteriorating the concordance between the results of the two tests, the I-ELISA appeared to be slightly more sensitive than CFT (Se I-ELISA=0.917 [0.822; 0.992], 95% Credibility Interval (CrI) compared to Se CFT=0.860 [0.740; 0.967], 95% CrI). However, CFT was slightly more specific than I-ELISA (Sp CFT=0.988 [0.947; 1.0], 95% CrI) compared to Sp I-ELISA =0.952 [0.901; 1.0], 95% CrI).The tests were then associated with two different interpretation schemes. The series association increased the specificity of screening and could be used for pre-movement testing in rams from uninfected flocks. The parallel association increased sequence sensitivity, thus appearing more suitable for eradicating the disease in infected flocks. CONCLUSIONS: The high sensitivity and acceptable specificity of this I-ELISA kit support its potential interest to avoid the limitations of CFT. The two tests could also be used together or combined with other diagnostic methods such as semen culture to improve the testing strategy. The choice of test sequence and interpretation criteria depends on the epidemiological context, screening objectives and the financial and practical constraints.

Estimation of sensitivity and specificity of five serological tests for the diagnosis of porcine brucellosis.

While serological tests are essential in surveillance and control programs of animal diseases, to date none of the common serological tests approved in the EU (complement fixation test or Rose-Bengal test) has been shown to be reliable in routine individual diagnosis of porcine brucellosis, and some more recent tests like ELISA have not been fully evaluated yet. In the absence of a gold standard, this study allowed the estimation of sensitivities and specificities of these tests with a Bayesian approach using Markov Chain Monte Carlo algorithms. The pig population that was tested included 6422 animals from Metropolitan France. Serum samples were collected from a large population of pigs, representative of European swine population and tested with five brucellosis serological tests: Rose-Bengal test (RBT), fluorescence polarization assay (FPA), indirect ELISA (I-ELISA) and two competitive ELISAs (C-ELISA). The sensitivity and the specificity of each test were estimated. When doubtful results were excluded, the most sensitive and specific test was C-ELISA(2) (Se C-ELISA(2)=0.964, [0.907; 0.994], 95% credibility interval (CrI); Sp C-ELISA(2)=0.996, [0.982; 1.0], 95% CrI). When doubtful results were considered as negative, C-ELISA(2) was still the most sensitive and specific test (Se C-ELISA(2)=0.960, [0.896; 0.994], 95% CrI and Sp C-ELISA(2)=0.994, [0.977; 0.999], 95% CrI). The same conclusions were reached when doubtful results were considered as positive (Se C-ELISA(2)=0.963, [0.904, 0.994], 95% CrI and Sp C-ELISA(2)=0.996, [0.986; 1.0], 95% CrI).