An ELISA based on whole virus for the detection of antibodies to small-ruminant lentiviruses.

A new ELISA kit was developed, based on highly purified whole-virus antigen derived from the Swiss maedi-visna virus strain OLV. The sensitivity, specificity and accuracy of this assay were compared with that of an established ELISA based on recombinant GAG (group-specific antigens)-GST (glutathione S-transferase) fusion protein expressed in E. coli (GAG-GST ELISA). The whole-virus ELISA exhibits at least comparable specificity (99.3%) but higher sensitivity (98.6 versus 86.3%) and agreement with the 'true' status beyond chance in the detection of antiviral antibodies in serum from goats. Antibodies in milk samples are detected with higher specificity (98.9 versus 97.8%) but lower sensitivity (91.4 versus 98.2%) than in GAG-GST ELISA. The specificity of the new ELISA in the detection of antibodies in serum might be superior, since a set of 40 samples falsely rated positive in GAG-GST ELISA in routine diagnostic work was negative in the new ELISA. In both assays, milk samples can be tested instead of serum, although with slightly reduced sensitivity in the new ELISA. The major advantage of the new test kit is the low number of equivocal samples needing confirmation in a supplementary test. Results obtained with sheep sera indicate that the new ELISA kit is also suitable for the detection of antibodies to maedi-visna virus.

Diagnosis of bovine virus diarrhoea by two enzyme-linked immunosorbent assays.

Two enzyme-linked immunosorbent assays (ELISAs) for the diagnosis of bovine virus diarrhoea (BVD) are described: CHEKIT-BVD-VIRUS and CHEKIT-BVD-SERO. The first test detects virus antigen in leucocytes, resulting in identification of persistently-infected animals, while the second detects antibodies to BVD virus (BVDV). It is well known that even persistently-infected animals may have antibodies to heterologous BVDV strains. These animals are still negative to the CHEKIT-BVD-SERO test because of immunotolerance to conserved virus antigens. Data on these two tests are summarised and a scheme is presented for the diagnosis of BVD using a combination of these two tests.

Enzyme-linked immunosorbent assay (ELISA) for the detection of antibodies against Salmonella enteritidis in chicken blood or egg yolk.

Tracing of flock infection remains one of the most serious unsolved problems of controlling salmonellosis in poultry. In order to overcome this problem, a serological test kit for the detection of antibody to Salmonella enteritidis (1, 9, 12:[f], g, m, [p]:[1, 7]) in chicken flocks was developed. In this study, samples of antisera and the yolk of eggs from different chicken flocks were tested with the ELISA kit, and the resulting flock profiles were compared. The test system clearly allowed a differentiation between flocks which were positive and flocks which were negative for S. enteritidis. Sera from stocks infected with S. typhimurium (1, 4, (5), 12:i:1, 2) or S. heidelberg (1, 4, (5), 12:r, 1, 2) were also analysed in order to determine the relative cross-reactivity in the test. No false-positive results could be shown in the case of S. heidelberg; cross-reactions with antibodies against S. typhimurium were found in 2.5% to 10% of the samples from a particular flock. The test kit could also be used for the analysis of egg yolk samples without time-consuming purification procedures. Specific antibodies were detected in high dilutions of positive egg yolks, thus enabling a rapid screening for S. enteritidis-positive chicken flocks.

Potency of two rabies vaccines in cats as determined by antibody assay and virulent virus challenge.

The persistence of immunity induced by a modified live virus rabies vaccine (SAD strain) and an inactivated rabies vaccine combined with panleukopenia vaccine in cats was studied serologically and by virulent rabies virus challenge. The source of challenge virus was a suspension of a dog salivary gland. All 16 cats vaccinated with the inactivated vaccine developed high antibody titres and 15 were protected against the virus challenge. All 8 cats vaccinated with the MLV vaccine produced a serological immune response but 5 cats were not protected against the virus challenge. Some reasons for this phenomenon are discussed.

Potency testing of inactivated rabies vaccines in mice, dogs and cats.

The high variability that exists in the NIH potency test for inactivated rabies vaccines is well known. To control this variability, the use of a reference preparation of rabies vaccine in parallel with the test vaccines is recommended. However, our data indicate, that the NIH test is more variable when calculating antigenic values using the reference vaccine CRV1 than when calculating only PD50 values. We immunized the mice with a single dose of different vaccine dilutions. As our results suggest, the antibody assay in immunized mice used for the NIH test, seems to be the best possible manner to determine the potency of inactivated rabies vaccines. The antigenic value of the NIH test does not correlate with the antibody status in immunized cats and dogs, but a correlation between antibody titres in mice and dogs appears to exist.

[Progression of the rabies virus in the visual system of the rat]. / Etude de la progression du virus rabique dans le système visuel du rat.

The CVS rabies virus, inoculated in the anterior chamber of the eye, is transported from the retina to the central nervous system only along the accessory optic tract and invades transsynaptically its terminal nuclei. On the other hand the retino-geniculo-cortical system is affected much later. Thus the virus shows a special affinity for a well defined neuronal system and behaves as a precise tracer of its intracerebral connections.

Enzyme linked immunoassay and fluorescent antibody techniques in the diagnosis of viral diseases using staphylococcal protein-A instead of anti-gamma-globulins.

Staphylococcal protein-A (SpA) is known to interact with the crystallizable fragment (Fc) of IgG molecules from several species. In the present study, SpA coupled to either fluorescein isothiocyanate (FITC) or peroxidase was used in place of antisera to IgG for the fluorescent antibody (FA) techniques and the enzyme linked immunoassay (ELISA). The SpA conjugates produced low background staining when applied in these techniques, and provide a rapid, highly specific and sensitive means for the identification of viral isolates and the detection of serum antibodies. Moreover, SpA is a single reagent that replaces various preparations of anti-gamma globulin against many species. SpA-FITC conjugate was successfully applied for the identification of pseudorabies virus, hog cholera virus, swine vesicular disease virus, transmissible gastroenteritis virus, porcine parvovirus and porcine enteroviruses. Antibody titers against the mentioned viruses could be determined semi-quantitatively in the indirect FA test with SpA-FITC. In our laboratory the ELISA became a routinely practicable serological test for the detection of antibodies only after we introduced SpA-peroxidase as a marker for the IgG.