False Positive Animals Research Articles

Experimental study of silkworm larvae plasma colorimetry based on immune cascade reaction in accurate diagnosis of periprosthetic joint infection

To investigate the diagnostic efficacy of silkworm larvae plasma (SLP) colorimetry in the accurate diagnosis of periprosthetic joint infection (PJI). Ninety healthy male New Zealand white rabbits were used for knee arthroplasty with Swanson prosthesis. Then they were randomly divided into 3 groups according to different pathogenic bacteria: group A ( Staphylococcus aureus group), group B ( Staphylococcus epidermidis group) and group C ( Escherichia coli group), with 30 rats in each group. The PJI model was prepared by knee injection with 1 mL of pathogenic bacteria of different concentrations. Samples were taken before inoculation and at 7, 14, and 21 days after inoculation, and based on the 2018 PJI Philadelphia International Consensus diagnostic criteria, the success rate of modeling among 3 groups of experimental animals was determined. The sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic efficiency of SLP colorimetry were calculated. At 21 days after inoculation, 26, 18, and 23 rabbits in groups A, B, and C were diagnosed as infection, respectively. The success rates of modeling were 86.7%, 60.0%, and 76.7%, respectively, showing no significant difference among the 3 groups ( χ 2=5.724, P=0.073). The results of PJI colorimetry showed that 1 false-positive animal (specificity 75.0%) appeared in group A at 7 days, and the specificity of SLP increased to 100.0% over time (on 14 and 21 days); on 14 and 21 days, another animal appeared false-negative results (sensitivity decreased from 100.0% to 96.2%). One false-positive animal appeared in group B at 7 days (specificity 91.7%), the specificity returned to 100.0% over time; 1 and 4 false-negative animals appeared at 14 and 21 days, respectively (sensitivity 94.4% and 83.3%, respectively). In group C, two false-positive animals (specificity 71.4%) were found at 7 days, and then returned to 100.0%. The diagnostic efficiency of groups A and C was very high at 21 days (96.7% and 100.0%), even for the low virulence Staphylococcus epidermidis in group B, the diagnostic efficiency could be maintained at 90.0% (21 days), and the overall diagnostic efficiency was very good (95.6%). SLP colorimetry has high sensitivity, specificity, and diagnostic efficiency in the diagnosis of PJI, which is a potential diagnostic method.

Brucella melitensis B115-based ELISA to unravel false positive serologic reactions in bovine brucellosis: a field study

BackgroundBrucellosis is a zoonosis whose incidence is not declining worldwide despite the global effort to control the disease. Accurate and precise diagnosis is a crucial step in any prophylaxis program but single tests to unequivocally detect animals infected with Brucella spp. are currently unavailable. In Italy, serological diagnosis of bovine brucellosis is performed with two official tests: a rapid agglutination test (i.e., Rose Bengal Plate test, RBPT) and a complement fixation test (CFT) that detect antibodies directed mainly to the smooth lipopolysaccharide (S-LPS). Neither of the two tests is able to avoid the detection of false positive serological reactions (FPSRs) caused by bacteria sharing S-LPS components with Brucella spp. and responsible for the single reactors (SR) phenomenon. A B. melitensis R strain-based ELISA showed a good diagnostic performance in unravelling FP animals; however, since a limited number of animals were analyzed in that study, a large field study was conducted here to discriminate between Brucella-infected from FP animals, with the final aim of reducing the unnecessary slaughter of the latter. An ELISA based on a R strain of Brucella, i.e., Brucella melitensis B115, was employed to measure specific IgG responses in a collection of bovine sera (n = 648). Sera were obtained from 180 farms (either officially brucellosis-free or not brucellosis-free) recruited during an extended period of time (2014–2018) and were preliminarily assayed with the official tests by the Italian Reference Centers and then subjected to the ELISA.ResultsNegative sera, when subjected to the ELISA, gave O.D. values below the cutoff; SR sera, i.e. RBPT positive and CFT negative, as well as double positive (DP) sera, i.e. RBPT and CFT positive, gave O.D. values that were below the cutoff. All positive sera, i.e. from Brucella-infected animals, were RBPT positive and CFT positive (ICFTU ranging from 20 to 1280) and gave ELISA O.D. values above the cutoff.ConclusionsThe B. melitensis B115-based ELISA systematically unravelled all false positive (FP) sera while confirming the diagnosis in Brucella-infected animals. Thus, the test employed in the present study may complement the official assays to avoid the costly slaughter of FP animals.

Towards Risk-Based Test Protocols: Estimating the Contribution of Intensive Testing to the UK Bovine Tuberculosis Problem

Eradicating disease from livestock populations involves the balancing act of removing sufficient numbers of diseased animals without removing too many healthy individuals in the process. As ever more tests for bovine tuberculosis (BTB) are carried out on the UK cattle herd, and each positive herd test triggers more testing, the question arises whether ‘false positive’ results contribute significantly to the measured BTB prevalence. Here, this question is explored using simple probabilistic models of test behaviour. When the screening test is applied to the average UK herd, the estimated proportion of test-associated false positive new outbreaks is highly sensitive to small fluctuations in screening test specificity. Estimations of this parameter should be updated as a priority. Once outbreaks have been confirmed in screening-test positive herds, the following rounds of intensive testing with more sensitive, albeit less specific, tests are highly likely to remove large numbers of false positive animals from herds. Despite this, it is unlikely that significantly more truly infected animals are removed. BTB test protocols should become based on quantified risk in order to prevent the needless slaughter of large numbers of healthy animals.

Evaluation of different antigens in a seroepizootiological survey of trichinellosis by enzyme-linked immunosorbent assay

Antigen isolated from the large-particle fraction of the muscle Trichinella spiralis larvae (PAW), excretory/secretory (E/S) and crude worm extract (CWE) antigens were evaluated in a seroepizootiological survey of trichinellosis by the enzyme-linked immunosorbent assay (ELISA). The ELISA using PAW antigen yielded 16 positive animals (1.6%), E/S antigen revealed 21 (2.1%) positive, and the highest number of positive (23 or 2.3%) were obtained using CWE antigen. Parasitological post-mortem examination of all seropositive animals showed five and seven false-positive animals when E/S and CWE antigens were used, respectively.