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  • Author or Editor: Lurinda J. Burge x
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Summary

Cell extracts that were prepared from blood mononuclear leukocytes from 66 samples obtained from 6 clinically normal calves contained mean 2′,5′-oligoadenylate (2′,5′-oligo[A]) synthetase activity sufficient to synthesize 186 ± 82 pmol of 2′,5′-oligo(A)/h/106 cells. Calves had no measurable serum interferon (ifn) activity. Five calves were given im injections of 104, 105, 5 × 105, 106, and 107 U of bovine ifn-α1/kg of body weight at 2-week intervals. Five dosing sequences were used with a 5 × 5 Latin square design so that each calf received each dose once. Activity of 2′,5′-oligo(A) synthetase increased at 24 hours in response to all dosages of ifn and then declined following first-order kinetics, with an apparent half-life (t½) of 2.1 ± 0.5 days. The area under the concentration-time curve for 2′,5′-oligo(A) synthetase increased with dose of ifn more rapidly than did peak response. Serum ifn that was measured at 1-day intervals following administration of ifn was consistently measurable only at dosages above 106 U of ifn/kg. The t½ for circulating ifn was 12.4 ± 1.0 hours. Over all dosages, increases in 2′,5′-oligo(A) synthetase activity were measurable for 3.5 days longer than were increases in ifn following im injection of ifn. None of the calves developed detectable anti-ifn antibodies.

Free access
in American Journal of Veterinary Research

Abstract

Objective—To evaluate diagnostic tests used for detection of bovine viral diarrhea virus (BVDV) and determine the prevalence of BVDV subtypes 1a, 1b, and 2a in persistently infected (PI) cattle entering a feedlot.

Design—Prospective study.

Animals—21,743 calves.

Procedures—Samples were obtained from calves initially testing positive via antigen capture ELISA (ACE) performed on fresh skin (ear notch) specimens, and ACE was repeated. Additionally, immunohistochemistry (IHC) was performed on skin specimens fixed in neutral-buffered 10% formalin, and reverse transcriptase PCR (RT-PCR) assay and virus isolation were performed on serum samples. Virus was subtyped via sequencing of the 5′ untranslated region of the viral genome.

Results—Initial ACE results were positive for BVDV in 88 calves. After subsequent testing, results of ACE, IHC, RT-PCR assay, and viral isolation were positive in 86 of 88 calves; results of all subsequent tests were negative in 2 calves. Those 2 calves had false-positive test results. On the basis of IHC results, 86 of 21,743 calves were PI with BVDV, resulting in a prevalence of 0.4%. Distribution of BVDV subtypes was BVDV1b (77.9%), BVDV1a (11.6%), and BVDV2a (10.5%).

Conclusions and Clinical Relevance—Rapid tests such as ACE permit identification and segregation of PI cattle pending results of further tests, thus reducing their contact with the rest of the feedlot population. Although vaccines with BVDV1a and 2a components are given to cattle entering feedlots, these vaccines may not provide adequate protection against BVDV1b.

Full access
in Journal of the American Veterinary Medical Association