Specificity enhancement of polyclonal antisera by the induction of tolerance to unwanted cross‐reacting determinants

Interlaboratory ring test of time-resolved fluoroimmunoassays for zeranol and alpha-zearalenol and comparison with zeranol test kits

Many zeranol immunoassay test kits cross-react with toxins formed by naturally occurring Fusarium spp. fungi, leading to false-positive screening results. This paper describes the evaluation and application of recently published, dry reagent time-resolved fluoroimmunoassays (TR-FIA) for zeranol and the toxin alpha-zearalenol. A ring test of bovine urine fortified with zeranol and/or alpha-zearalenol in four European Union National Reference Laboratories demonstrated that the TR-FIA tests were accurate and robust. The alpha-zearalenol TR-FIA satisfactorily quantified alpha-zearalenol in urine fortified at 10-30 ng ml(-1). The specificity-enhanced zeranol TR-FIA accurately quantified zeranol in the range 2-5 ng ml(-1) and gave no false-positive results in blank urine, even in the presence of 30 ng ml(-1) alpha-zearalenol. Zeranol TR-FIA specificity was demonstrated further by analysing incurred zeranol-free urine samples containing natural Fusarium spp. toxins. The TR-FIA yielded no false-positive results in the presence of up to 22 ng ml(-1) toxins. The performance of four commercially available zeranol immunoassay test kits was more variable. Three kits produced many false-positive results. One kit produced only one potential false-positive using a protocol that was longer than that of the TR-FIA. These TR-FIAs will be valuable tools to develop inspection criteria to distinguish illegal zeranol abuse from contamination arising from in vivo metabolism of Fusarium spp. toxins.

Development and validation of dry reagent time-resolved fluoroimmunoassays for zeranol and alpha-zearalenol to assist in distinguishing zeranol abuse from Fusarium spp. toxin contamination in bovine urine

Zeranol, an oestrogenic growth promoter in food animals, is banned within the European Union (EU). However, commercially available immunoassay kits for zeranol cross-react with toxins formed by naturally occurring Fusarium spp. fungi, leading to false-positive screening results. This paper describes the validation of a specificity enhanced, rapid dry reagent time-resolved fluoroimmunoassay (TR-FIA) for zeranol (recovery 99%, limit of detection 1.3 ng ml(-1)) demonstrating that up to 150 ng ml(-1) of Fusarium spp. toxins in urine do not lead to false-positive results. This assay will assist EU Member States to implement Council Directive 96/23/EC, which requires states to monitor for potential abuses of zeranol. A similar TR-FIA for the Fusarium spp. toxin alpha-zearalenol, using the same sample extract, is also described (recovery 68%, limit of detection 5.6 ng ml(-1)). Only the addition of diluted sample extract is required to perform these dry-reagent TRFIAs, the results being available within 1h of extract application. The EU-funded project 'Natural Zeranol' (FAIR5-CT97-3443) will use these fluoroimmunoassays to screen bovine urine in four Member States to gather data on the seasonality of Fusarium spp. toxin contamination of urine and the incidence of zeranol screening test positives.

Biochemical characterization of salmon pancreas disease virus

Salmon pancreas disease virus (SPDV) has been shown to cause severe economic losses in farmed Atlantic salmon (Salmo salar) and has been reported to occur in Europe, Scandinavia and the United States. This paper describes the biochemical characterization of SPDV in terms of its RNA and protein composition. SPDV was purified by precipitation from infected Chinook salmon embryo (CHSE-214) cell-culture supernatant and sucrose density-gradient centrifugation. Fractions containing virus were identified by an immunodot blot assay using an SPDV-specific MAb. Two major proteins with molecular masses of approximately 55 and 50 kDa, putatively identified as the E1 and E2 alphavirus glycoproteins respectively, were detected when purified virus preparations were analysed by PAGE. Radiolabelling experiments indicated that SPDV infection of CHSE-214 cells did not shut-off host-cell protein synthesis, making attempts to identify virus-specific proteins unsuccessful. However, radioimmunoprecipitation assay (RIPA) experiments showed that two SPDV-specific MAbs reacted with a protein in the 50-55 kDa range. Northern blot hybridization with cloned cDNA probes indicated that infected cells contained RNA species of approximately 11.4 and 4 kb, which correspond to the genomic and subgenomic RNAs specified by SPDV. The results described are consistent with SPDV being characterized as an alphavirus.

Comparison of the effects of injections of nortestosterone phenylpropionate at single and multiple sites in cattle on the detection of its residues in plasma, urine and bile

The synthetic androgen 17 beta-19-nortestosterone (beta-NT) has been used illegally as a growth promoter in cattle production in the European Union. The elimination of beta-NT and its metabolites in plasma and urine was studied in cattle which had received intramuscular injections of its phenylpropionate ester (NTPP) at either single or multiple sites at a dose rate of 1 mg/kg bodyweight. In both groups, the plasma concentrations of beta-NT, measured by enzyme immunoassay, were consistently greater than the assay's limit of quantification (0.24 ng/ml) during days 1 to 7 of the study. The mean (sd) maximum plasma concentration (Cmax) was significantly greater in the multiply injected animals (4.4 [0.48] v 2.7 [0.15] ng/ml), but other plasma pharmacokinetic parameters, AUC, CL, T1/2 beta, Tmax and MRT, were not significantly different in the two groups. The equivalent urinary concentrations exceeded the limit of quantification of the assay (4.5 ng/ml) for up to 24 days after injection. In a second study, the biliary concentrations of beta-NT and its 17 alpha-epimer (alpha-NT) were measured by gas chromatography-high resolution mass spectrometry after cattle were injected intramuscularly at either single or multiple sites with NTPP. Only alpha-NT was detected in bile for up to 62 days after injection at concentrations above the limit of quantification of the assay (0.7 ng/ml). It is concluded that in some animals, intramuscular injections of NTPP at several sites may decrease the period after injection during which free beta-NT and its metabolites are detectable in plasma and urine. After the injection of NTPP, alpha-NT was detected in bile for longer than it was detected in plasma or urine.

Nortestosterone is not a naturally occurring compound in male cattle

Nortestosterone (beta-NT) is a hormonal growth promoter banned from livestock production in the EU. Following injection, the major metabolite in cattle is the 17 alpha-epimer (alpha-NT). However, this also occurs naturally in pregnant cattle. It is not known whether alpha-NT is also endogenous to intact or castrated male cattle. Three surveys were undertaken to assess whether alpha-NT is naturally produced in this subset of the population. Bile samples from a total of 1,281 cattle (73 bulls and 1,208 steers) from 366 herds were collected at slaughter and initially screened by using a semi-automated EIA with multi-analyte immunoaffinity chromatography (IAC) clean-up. Bile samples from a further 38 male cattle (10 bulls and 28 steers) were analysed by high-resolution gas chromatography-mass spectrometry (GC-MS) with IAC pretreatment. Only samples containing more than 2 ng/ml alpha-NT were subjected to GC-MS. With 2 ng/ml alpha-NT as a threshold for confirmatory testing, the false positive rate of the screening EIA was 1.8%. Bulls (n = 16) and steers (n = 179) from government farms (n = 2) and which were not treated with exogenous beta-NT, did not have measurable concentrations of alpha-NT in their bile. Bulls (n = 35) and steers (n = 606) taken from herds (n = 204) which had no previous history of illegal growth promoter abuse also did not have alpha-NT in their bile. Of 32 bulls and 451 steers of unknown treatment history sampled from herds (n = 160), 56 steers from 19 herds contained GC-MS confirmed concentrations of alpha-NT higher than the limit of quantification of the assay LOQ (0.7 ng/ml). Of these animals, two had beta-NT-containing injection sites and five had residues of the beta-agonists clenbuterol and mabuterol. Examination of the animal movement and ownership histories of the 56 confirmed positive animals strongly suggested that exogenous beta-NT had been administered at the presenting farm. It is concluded that alpha-NT is not endogenous to this subset of the cattle population and that detection of this hormone in bile from bulls and steers constitutes evidence of abuse.