Comparison of an enzyme-linked immunosorbent assay using monoclonal antibodies and a complement fixation test for cattle vaccinated and infected with Brucella abortus

A competitive enzyme-linked immunosorbent assay (ELISA) using a monoclonal antibody conjugated to horseradish peroxidase MA(A) and a complement fixation test (CFT) were applied to sera collected over a two-year period from 60 cattle challenged with Brucella abortus strain 544. Forty-eight of the cattle were previously vaccinated with B. abortus strain 19 (S19) or B. abortus strain 45/20 (45/20). After challenge 33 of the cattle remained uninfected and nine of the 27 infected cattle showed aberrant reactions by the CFT. The performance of the MA(A) ELISA was as follows: after vaccination, the MA(A) ELISA, like the CFT, was unable to differentiate infected cattle from those recently vaccinated with S19. After challenge the MA(A) ELISA gave results comparable with the CFT for those cattle with aberrant reactions. For the non-infected cattle there was a similar number of weeks after challenge when both tests were negative. It is suggested that the main advantage of the MA(A) ELISA when compared with the CFT lies in its relatively simple test procedure.     

Evaluation of the enzyme-linked immunosorbent assay for detecting Brucella abortus antibodies.

The specificity of enzyme-linked immunosorbent assays (ELISA) corresponds to conventional methods for detecting brucella antibodies in bovine serum. The ELISA test detected brucella antibodies early in only 12.5% of the cattle sera tested. Also, the sensitivity of ELISA was comparable to complement-fixation and Rivanol methods, but less sensitive than the standard tube agglutination method.     

Validation of an indirect enzyme-linked immunosorbent assay for the detection of antibody against Brucella abortus in cattle sera using an automated ELISA workstation

An automated indirect enzyme-linked immunosorbent assay (I-ELISA) for the serological diagnosis of bovine brucellosis was developed and validated in-house. A total of 4,803 cattle sera from South Africa (n = 3,643), Canada (n = 652), Germany (n = 240), France (n = 73) and the USA (n = 195) was used. The South African panel of sera represented 834 sera known to be positive by the Rose Bengal test (RBT), serum agglutination test (SAT) and complement fixation test (CFT), 2709 sera that were negative by CFT, and 100 sera from animals vaccinated with a standard dose of Brucella abortus strain 19. Overseas sera were obtained from reference non-vaccinated brucella-free cattle (n = 834), naturally infected (n = 72), experimentally infected (n = 71), and vaccinated animals (n = 83). Also 100 sera collected from cattle in Canada and known to be positive by competitive ELISA (C-ELISA) were used. The intermediate ranges ("borderline" range for the interpretation of test results) were derived from two-graph receiver operating characteristics analysis. The lowest values of the misclassification cost-term analysis obtained from testing overseas panels, covered lower I-ELISA cut-off PP values (0.02-3.0) than those from local panels (1.5-5.0). The relatively low cut-off PP values selected for I-ELISA were due to the fact that the positive control used represents a very strong standard compared to other reference positive sera. The greater overlap found between negative and positive cattle sera from South Africa than that between reference overseas panels was probably due to the different criteria used in classifying these panels as negative (sera from true non-diseased/non-infected animals) or positive (sera from true diseased/infected animals). The diagnostic sensitivity of the I-ELISA (at the optimum cut-off value) was 100% and of the CFT 83.3%. The diagnostic specificity of I-ELISA was 99.8% and of the CFT 100%. Estimate of Youden's index was higher for the I-ELISA (0.998) than that for the CFT (0.833). Analysis of distribution of PP values in sera from vaccinated and naturally infected cattle shows that in vaccinated animals all readings were below 31 PP where in infected ones these values represented 43%. Therefore, it appears that I-ELISA could be of use in identifying some naturally infected animals (with values > 31 PP), but more sera from reference vaccinated and infected animals need to be tested to further substantiate this statistically. Of 834 sera positive by RBT, SAT and CFT, 825 (98.9%) were positive in the I-ELISA. Compared to C-ELISA the relative diagnostic sensitivity of the I-ELISA was 94% and of the CFT 88% when testing 100 Canadian cattle sera. Of 258 South African cattle sera, of which 183 (70.9 %) were positive by the I-ELISA and 148 (57.4 %) by the CFT, 197 (76.4%) were positive by C-ELISA when re-tested in Canada. One has to stress, however, that Canadian C-ELISA has not been optimised locally. Thus, the C-ELISA was probably not used at the best diagnostic threshold for testing South African cattle sera. This study shows that the I-ELISA performed on an automated ELISA workstation provides a rapid, simple, highly sensitive and specific diagnostic system for large-scale detection of antibodies against B. abortus. Based on the diagnostic accuracy of this assay reported here, the authors suggest that it could replace not only the currently used confirmatory CFT test, but also the two in-use screening tests, namely the RBT and SAT.     

Rapid detection of canine parvovirus in feces using monoclonal antibodies and enzyme-linked immunosorbent assay

Monoclonal antibodies were used to develop a double antibody enzyme-linked immunosorbent assay for the detection of canine parvovirus (CPV) antigen in fecal samples. The assay was specific for the hemagglutinating protein of CPV and detected as little as 1.5 ng of virus within a 15-minute incubation period. The use of monoclonal antibodies against 2 epitopes on the CPV antigen permitted the simultaneous addition of test sample and enzyme-conjugated antibody, thus considerably simplifying the manipulations required for the assay. Results were visually determined without special instrumentation. Clinical studies revealed greater than 95% correlation between enzyme-linked immunosorbent assay results and hemagglutination titers.     

An enzyme-linked immunosorbent assay for detection of antibodies against bovine pestivirus

A competitive enzyme-linked immunosorbent assay was developed and compared with the serum neutralisation test for bovine pestivirus using 508 cattle sera and serial serum samples from a goat hyperimmunized with five bovine pestivirus isolates. There was 96.7% agreement between the two tests. The relative sensitivity of the enzyme-linked immunosorbent assay compared to the serum neutralisation test was 95.2% and the relative specificity was 99.4%. The titres of individual animals in the assay did not show a close correlation with serum neutralisation test titres. This may be because the antibodies measured in the two tests are directed against different viral proteins. The enzyme-linked immunosorbent assay has the advantage of being quicker and cheaper than the serum neutralisation test. The configuration used in the ELISA means sera from all species can be tested for pestivirus antibody using the same set of reagents.     

An enzyme-linked immunosorbent assay for the detection of vesicular stomatitis virus antibodies

A liquid-phase enzyme-linked immunosorbent assay (ELISA) was developed for the detection of vesicular stomatitis virus (VSV) types New Jersey (VSV-NJ) and Indiana subtype Indiana I (VSV-IND₁) antibodies in the sera of naturally and experimentally infected cattle, horses and swine. Four different VSV preparations were compared for use as antigen in the ELISA: virus used in neutralization tests, complement-fixation antigen, immunodiffusion ager gel antigen and viral glycoprotein. Comparative antibody titration results of virus neutralization (VN) and ELISA showed no statistically significant difference between serum titers obtained with the four antigens to VSV-NJ (P=0.21) and VSV-IND₁ (P=0.14). The viral glycoprotein antigen was incorporated in the ELISA system because it is non-infectious and induces neutralizing antibodies. The reliability and variability of the ELISA was determined by testing 516 bovine, equine and swine sera which originated from areas free of vesicular stomatitis, and by testing 186 sera from areas where outbreaks occur. ELISA and VN results were correlated (P < 0.001 for both serotypes), and no statiscafically difference was found between replications of the tests. The ELISA allows the testing of a larger number of sera in a shorter time than is possible with the VN test and it can be used in diagnostic laboratories in VSV-free areas for the support of epidemiological surveillance programs.     

Detecting Mycoplasma bovis in milk by enzyme-linked immunosorbent assay, using monoclonal antibodies

Enzyme-linked immunosorbent assay, using monoclonal antibodies, was used to detect Mycoplasma bovis in milk samples from a dairy experiencing an epizootic of mastitis. This method was specific (100%) for M bovis. Broth enrichment increased the sensitivity from 65% to 86%, compared with standard culture methods.     

A competitive enzyme immunoassay for the detection of bovine antibodies to Brucella abortus using monoclonal antibodies

A competitive enzyme immunoassay (EIA) for the detection of circulating bovine antibodies to Brucella abortus has been developed using horseradish peroxidase conjugated monoclonal antibodies (MAb) raised against B. abortus cell surface antigens. Antibodies present in the serum of either vaccinated or infected cattle can apparently displace the conjugated MAb from the lipopolysaccharide antigen (LPS) in a quantitatively different manner allowing an assessment of immune status of the animal. The results from a panel of sera from animals with a known status of vaccination or infection indicated that the test was more selective in the detection and discrimination of infected from uninfected or immunized animals, than conventional complement fixation, agglutination or indirect enzyme immunoassay procedures.     

Use of enzyme-linked immunosorbent assay for detection of antibodies to Brucella ovis in sheep: field trial

An enzyme-linked immunosorbent assay (ELISA), using an autoclave-extracted soluble antigen, for the detection of serum antibodies to Brucella ovis in sheep was developed. The test seemed to be both sensitive and specific, on the basis of the control groups studied. The antigen showed no deterioration in prepared plates stored at -70 C for up to a year. The ELISA was used in conjunction with palpation of rams for epididymal lesions as a means to detect and control B ovis infection in a naturally infected flock. All rams were evaluated by the ELISA. At the time that the first blood sample was obtained, all positive and suspicious reactors were removed. With subsequent blood sample collections, only the positive reactors were removed. Brucella ovis was not isolated from any rams during the following year, and none of the mature breeding rams developed epididymal lesions.     

Enzyme immunoassay using mouse monoclonal anti-bovine antibodies for the detection of Brucella abortus antibodies in cow milk

Individual milk samples and artificially constructed tank milk samples from cows with naturally occurring brucellosis were examined by the enzyme-linked immunosorbent assay (ELISA) using sonicated B. abortus S-99 antigen, and mouse monoclonal anti-bovine IgM, IgA, and IgG1 conjugates. ELISA results were compared with the results of the milk ring test using either 1 ml milk (MRT-1) or 8 ml milk (MRT-8). The ELISA using mouse monoclonal anti-bovine IgG1 conjugate was sensitive and specific. In testing individual milk samples and constructed tank milk samples containing milk with low titers in the MRT-1 the ELISA was superior to the MRT-1, and MRT-8. In testing other milk samples, the ELISA was as sensitive or slightly less sensitive than the MRT-8. From a total of 5,910 milk samples collected from cows free from brucellosis, only 24 (0.4%) samples tested positive in the ELISA. All 500 tank milk samples collected from farms negative for brucellosis tested negative in the ELISA. We concluded that the ELISA is a good substitute for the MRT-1 to detect antibodies against Brucella in milk from individual cows. When tank milk is tested for antibodies against Brucella, however, both the MRT-8 and the ELISA should be used.     

An enzyme-linked immunosorbent assay for the detection of antibodies to Marek's disease virus

A reproducible enzyme-linked immunosorbent assay (ELISA) using Marek's disease virus (MDV)-infected cells for the detection of antibodies to MDV is described. The optimum number of MDV-infected chicken embryo fibroblasts (CEF) was 5 X 10(4)/well, and test sera were positive at 1:400 dilutions. Compared with a purified virus preparation, MDV-infected CEF produced high specific and low nonspecific reactivities. Wells coated with whole cells could be stored at 4 C or -20 C for at least 3 months without loss of reactivity. With antibody-negative sera, the cutoff absorbency was 0.20 units. The ELISA was 20-to-40-fold more sensitive than indirect immunofluorescence. Homologous combinations of antisera in wells coated with CEF infected with different MDV serotypes were more reactive at higher dilutions than were heterologous combinations. The procedure described is specific and suitable for large-scale screening of both chicken and monoclonal antibodies against MDV.     

An enzyme-linked immunosorbent assay for detection of antibodies to exogenous avian leukosis virus

A microplate enzyme-linked immunosorbent assay (ELISA) for detecting antibodies to avian leukosis virus (ALV) of subgroups A and B in infected chickens was developed with the use of Rous-associated virus (RAV)-1 (subgroup A) and RAV-2 (subgroup B) antigens purified by sucrose-gradient centrifugation. The antigen was used for ELISA after treatment with Triton X-100. In the ELISA, the subgroup viral antigen reacted strongly with homologous antiserum but also reacted with heterologous antiserum. Tests with serum absorbed with purified homologous and heterologous virus and tests for antigen-blocking by group-specific antibodies to ALV revealed that the reaction was caused mainly by subgroup-specific antibodies. The ELISA was 8 to 32 times more sensitive than the virus-neutralization (VN) test and detected antibodies to ALV earlier than the VN test in chickens infected experimentally with RAV-1 and RAV-2. In field application of the ELISA, 44.2% of 484 chicken sera were positive for RAV-1 and/or RAV-2 antigen, and 80.4% of flocks were positive. These findings indicate that ELISA is superior to the VN test in sensitivity, simplicity, rapidity, and applicability for large-scale field surveys for ALV infection.     

A monoclonal antibody-blocking enzyme-linked immunosorbent assay for the detection of serovar-specific antibodies to Haemophilus paragallinarum

Two monoclonal antibody-blocking enzyme-linked immunosorbent assays (B-ELISAs) were developed to detect serovar-specific antibodies to Haemophilus paragallinarum. One assay detected antibodies against serovar A and the other antibodies against serovar C. The assays were evaluated with sera derived from disease-free chickens as well as chickens experimentally immunized and/or challenged with H. paragallinarum strains 0083 (serovar A), Modesto (serovar C), or HP31 (serovar C). When tested with 440 negative sera (170 from a specific-pathogen-free and 30 from each of nine commercial layer flocks), both tests gave only a single false-positive reaction. The use of the B-ELISAs with the experimentally produced sera showed the assays to be serovar specific. With the exception of one serum, the serovar A B-ELISA detected antibodies only in the chickens vaccinated with 0083. Similarly, with the exception of one serum, the serovar C B-ELISA detected antibodies only in those chickens vaccinated with Modesto or those chickens challenged with HP31. Overall, the serovar A B-ELISA had a specificity of 99.7% and a sensitivity of 78.7%, whereas the serovar C B-ELISA had a specificity of 99.8% and a sensitivity of 64.7%.     

Enzyme-linked immunosorbent assay for detecting antibodies to Brucella abortus in bovine milk and serum

An enzyme-linked immunosorbent assay (ELISA) method was evaluated for the detection of antibodies to Brucella abortus in cows milk. Milk samples from seropositive or -negative cows were sed to determine the distribution of absorbance values to classify milk as ELISA positive or ELISA negative. Brucella abortus was isolated from milk samples from 10 (45%) of the 22 cows whose milk and serum were ELISA positive. The ELISA was evaluated and determined to be an appropriate method for detecting antibodies to B abortus in bovine milk.     

An enzyme-linked immunosorbent assay for antibodies to Hepatozoon canis

Canine hepatozoonosis is a tick-borne protozoal disease caused in the Old World and South America by Hepatozoon canis. An enzyme-linked immunosorbent assay (ELISA) using purified H. canis gamont antigen was applied for the detection of antibodies reactive with H. canis. Evaluation of the ELISA with sera from naturally infected parasitemic dogs indicated that it was sensitive (86%), specific (97%), and comparable to the indirect fluorescent antibody test (IFAT) for the detection of H. canis antibodies. A variable degree of serologic cross-reactivity was found between sera from H. americanum-infected dogs and the H. canis antigen. Dogs experimentally infected with H. canis seroconverted 1-4 weeks post-infection (PI). Antibody levels peaked at 7-9 weeks PI and gradually declined thereafter remaining above the cut-off value until the conclusion of the study 7 months PI. The ELISA will be valuable for serological evaluation of dogs suspected of exposure to H. canis and for epidemiological studies.     

Sandwich enzyme-linked immunosorbent assay by using monoclonal antibody for detection of Clostridium perfringens enterotoxin

Sandwich enzyme-linked immunosorbent assay (ELISA) was developed for the quantitative estimation of Clostridium perfringens enterotoxin (CPE) with monoclonal and polyclonal antibodies as capturing and detecting antibodies, respectively. The dose-dependent relationship between absorbance at 405 nm and concentration of purified CPE was obtained over the range of 0.64-400 ng/ml. The sandwich ELISA was fond to detect crude CPE in culture and CPE in 10% fecal extracts. This method is convenient, rapid and sensitive for specific detection of CPE.     

Chicken IFN-gamma monoclonal antibodies and their application in enzyme-linked immunosorbent assay

Twelve mabs against native or recombinant chicken IFN-gamma were produced and characterized by virus neutralization, ELISA, and Western blot assays. No data were obtained to suggest that the form of the immunogen (native versus recombinant) influenced the antigenic specificity of the mabs produced. While only two antibodies inhibited the in vitro virus neutralizing activity of IFN-gamma, other evidence indicated that the specificity of these mabs was indeed directed against IFN-gamma. By Western blot analysis, all antibodies identified a 17-kDa IFN-gamma polypeptide. Using a direct binding ELISA incorporating these mabs, a high correlation with IFN-gamma detected by in vitro virus neutralization was observed. The IFN-gamma ELISA was also capable of measuring cytokine levels in the sera of chickens orally infected with Eimeria maxima. At 8 and 10 days post-primary infection, significantly higher (p<0. 001) levels of serum IFN-gamma were detected in E. maxima infected chickens compared to uninfected controls. These results indicate that a mab-based direct binding ELISA is suitable to measure chicken IFN-gamma in a variety of formats.     

An enzyme-linked immunosorbent assay for the detection of antibodies to avian reticuloendotheliosis virus using whole cell antigen

An enzyme-linked immunosorbent assay (ELISA) using reticuloendotheliosis virus-infected chick embryo fibroblasts as coating antigen is described for the detection of antibodies to reticuloendotheliosis virus in chicken sera. The ELISA was specific and during the early stages of infection more sensitive than an indirect fluorescent antibody test.     

Blocking enzyme-linked immunosorbent assay for detection of antibodies against bovine enterovirus

A blocking enzyme-linked immunosorbent assay (ELISA) was developed for detecting antibodies against bovine enterovirus (BEV) in bovine sera. In this ELISA, bovine serum samples were allowed to react with captured viral antigens (by specific chicken IgG), before the addition of specific mouse IgG for measuring non-occupied viral epitopes. The ELISA was slightly more sensitive and required a shorter time period than traditional serum neutralisation (SN). Among the 871 bovine serum samples tested so far, the titres produced by this assay had a significant correlation with those recorded by SN. The ELISA could be used as an alternative assay for SN in a large-scale BEV antibody investigation.     

H5 antibody detection by blocking enzyme-linked immunosorbent assay using a monoclonal antibody

Many commercial enzyme-linked immunosorbent assays (ELISAs) are unable to differentiate antibody responses to different avian influenza virus (AIV) subtypes. Developing an ELISA for specifically detecting the H5 antibody is the purpose of this study. Four monoclonal antibodies (Mabs) were raised using A/duck/Yunlin/04 (H5N2). They were confirmed as being specific to H5. Two of these antibodies showed hemagglutination inhibition (HI) activity using the HI test. Using immunodot blot assays, three Mabs recognized both Eurasian and American H5, whereas the other Mab recognized only the tested Eurasian H5 virus. When testing denatured H5 antigen, one of the Mabs lost its antigen binding activity using Western blotting. For detecting the H5 humoral response in serum, one monoclonal antibody was purified and labeled with horseradish peroxidase to set up a blocking ELISA. Chicken sera that blocked H5 Mab binding by > 29% were considered H5 antibody positive. Inhibition percentages for sera from chickens infected with other AIV subtypes, H1 to H15, were < 29%. This blocking ELISA was used for 478 field chicken serum samples. The results showed that the sensitivity and specificity of this ELISA were 98.3% (232/236) and 95.9% (232/242), respectively. This blocking ELISA could be used specifically for detecting the H5 humoral responses in chickens.