During October of 1984 an influenza epidemic occurred on mink farms in the coastal region of South Sweden. Six strains of an influenza A virus were isolated. All six isolates were of the H 10 subtype in combination with N4. The H 10 subtype in combination with various N subtypes was hitherto only known to occur in avian strains, the prototype being the A/chicken/Germany/N/49 (H 10N7) virus.
The present study shows that milk is an appropriate source for detection of seroreactors to bovine virus diarrhoea virus (BVDV). There was close agreement between antibody titres in serum and in skim milk, as determined by an indirect enzyme-linked immunosorbent assay. The antibody titres were usually lower in skim milk than in serum, but all seropositive cows (n = 84) were also skim milk-positive and all but one seronegative cow (n = 55) proved negative in skim milk.During lactation, the level of antibodies to BVDV in milk showed an inverse relationship to the amount of milk produced. However, there was a sufficient level of antibodies in milk throughout lactation to permit an adequate determination of BVDV antibody status in dairy cows. There was a mutual good agreement between milk antibody titre in the four mammary quarters, irrespective of milk cell count. Milk can be used to detect seroreactors to BVDV. Milk is preferable to blood in largescale epidemiological studies, since the sampling procedure is much simpler.
Summary
Two ELISA techniques were developed for the detection of antibodies to bovine viral diarrhoea virus (BVDV), an indirect and a competitive ELISA. The coating antigen was prepared from virus harvests which were 10 to 100 times larger than usual. This was achieved by culturing the cells in a growth medium with foetal calf serum devoid of IgG. The harvested BVDV was solubilized with detergent to increase the accessibility of antigens. By these modifications, the amount of antigen produced from one 120 cm2 bottle was sufficient to coat at least 50 microtitre plates.
The indirect ELISA was governed by a monoclonal antibody (MAb) to bovine IgG and the competitive ELISA by a MAb to BVDV. Preliminary results indicate that this latter MAb binds to a 20 K protein, present in both cytopathogenic and non‐cytopathogenic strains of BVDV.
Cattle sera were examined from the field as well as sera collected from a heifer following natural infection. There was a good correlation between the results obtained by the two ELISA techniques and in serum neutralization test. For routine examination of bovine serum samples the indirect ELISA applying a MAb to bovine IgG is recommended.
Zusammenfassung
Zwei ELISA‐Techniken wurden zum Nachweis von Antikörpern gegen bovines Virusdiarrhoe‐Virus (BVDV) entwickelt, ein indirekter und ein kompetitiver ELISA. Durch Kultur von Zellen in Wachstumsmedium mit IgG‐freien FKS wurden 10‐ bis 100fach höhere Virusausbeuten erzielt, die zur Beschichtung von Platten verwendet wurden. Das geerntete BVDV wurde mit Detergens behandelt, um die Antigenverfügbarkeit zu verbessern. Durch diese Modifikationen war die Ernte aus einer 120cm2‐Flasche ausreichend, um mindestens 50 Mikrotiterplatten zu beschichten.
Der indirekte ELISA benützt einen monoklonalen Antikörper (MAK) gegen bovines IgG und der kompetitive ELISA einen MAK gegen BVDV. Vorläufige Ergebnisse deuten darauf hin, daß der letztere MAK an ein 20 K Protein bindet, das sowohl in cytopathogenen als auch in nichtcytopathogenen BVDV‐Stämmen vorhanden ist. Untersucht wurden Rinderseren aus dem Feld sowie Seren einer Färse mit natürlicher BVDV‐Infektion. Die Ergebnisse der beiden ELISA‐Techniken zeigten eine gute Korrelation untereinander und mit dem Serum‐Neutralisationstest. Für die Routineuntersuchung von Rinderseren wird der indirekte ELISA mit dem MAK gegen bovines IgG empfohlen.
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