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in Journal of the American Veterinary Medical Association

Summary

Nine cns bovine herpesvirus type 1 (bhv-1) isolates, recovered from bovine brain samples submitted to the Texas Veterinary Medical Diagnostic Laboratories from 1974-1989, were compared by analyzing their dna restriction endonuclease (re) fragment migration pattern. Seven had pattern similar to that of the respiratory bhv-1 Cooper strain. The remaining 2 isolates, however, had variant patterns, similar to that of each other, but completely different from patterns for the other 7. The re patterns of these 2 variants were similar to published re patterns for 2 encephalitic or neuropathogenic bhv-1 strains — the Australian N-569 strain and the Argentine A-663 strain. One of the Texas encephalitic variants (No. 30326) was isolated from the cns of a calf that died during an epizootic of encephalitis in 1974. The other, designated TX-89, was isolated in 1989 from the cns of a 7-month-old feedlot steer with acute fatal encephalitis. Microscopic lesions of encephalitis with neuronal degeneration and intranuclear inclusions were observed for 3 of the 9 isolates, the 2 variant isolates (No. 30326 and TX-89), and a respiratory isolate. The remaining 6 cns isolates, all respiratory subtypes, were recovered from cattle that did not have clinical cns disease or gross or microscopic cns lesions; in 5 of these cattle, virus was recovered from at least 1 other organ (lungs) besides the cns. We conclude that the cns of calves can be naturally infected with 2 distinct bhv-1 subtypes, the respiratory and the encephalitic, and that the encephalitic subtype (subtype 3 or bhv-1.3) has been present in Texas cattle since at least 1974.

Free access
in American Journal of Veterinary Research

Abstract

Objective—To develop and validate an ex vivo model for study of adherence of Mannheimia haemolytica (formerly Pasteurella haemolytica) to respiratory tract mucosa of cattle and to use this model to confirm adherence of M haemolytica serovar 1 (Mh1) to several relevant respiratory mucosal surfaces.

Sample Population—Excised nasal, nasopharyngeal, turbinate, and tonsillar mucosal tissue from the bovine upper respiratory tract.

Procedure—Mh1 was radiolabeled by use of tritiated leucine. Various concentrations of labeled bacteria were incubated with bovine upper respiratory tract tissues for various times. Tissue was washed to remove nonadherent bacteria, and percentage of bacteria adhered (percentage of adherence) was estimated using radioactivity. Using an optimal inoculum concentration and incubation time, percentage of Mh1 adherence was compared on nasal, nasopharyngeal, turbinate, and tonsillar mucosal tissue, and adherence to nasopharyngeal tissue was confirmed by scanning and transmission electron microscopy.

Results—The optimal Mh1 inoculum concentration was 1 × 107 colony forming units/ml and incubation time was 3 hours. Percentage of adherence of Mh1 to nasopharyngeal tissue was greater than adherence to other tissue types.

Conclusions and Clinical Relevance—The ex vivo model maintained the functional and structural integrity of bovine upper respiratory tract mucosa, as confirmed by light and electron microscopy. Electron microscopy revealed participation of epithelial cell cilia and surface mucus in adherence of Mh1 to nasopharyngeal tissue. Adherence of Mh1 was confirmed in repeated assays, indicating that this organism adheres to upper respiratory tract mucosa of cattle. (Am J Vet Res 2001;62:805–811)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To evaluate economic effects and health and performance of the general cattle population after exposure to cattle persistently infected (PI) with bovine viral diarrhea virus (BVDV) in a feedlot.

Animals—21,743 high-risk calves from the southeastern United States.

Procedures—PI status was determined by use of an antigen-capture ELISA (ACE) and confirmed by use of a second ACE, reverse transcriptase–PCR assay of sera, immunohistochemical analysis, and virus isolation from sera. Groups with various amounts of exposure to BVDV PI cattle were used. After being placed in the feedlot, identified PI cattle were removed from 1 section, but PI cattle remained in another section of the feedlot. Exposure groups for cattle lots arriving without PI animals were determined by spatial association to cattle lots, with PI animals remaining or removed from the lot.

Results—15,348 cattle maintained their exposure group. Performance outcomes improved slightly among the 5 exposure groups as the risk for exposure to BVDV PI cattle decreased. Health outcomes had an association with exposure risk that depended on the exposure group. Comparing cattle lots with direct exposure with those without direct exposure revealed significant improvements in all performance outcomes and in first relapse percentage and mortality percentage in the health outcomes. Economic analysis revealed that fatalities accounted for losses of $5.26/animal and performance losses were $88.26/animal.

Conclusions and Clinical Relevance—This study provided evidence that exposure of the general population of feedlot cattle to BVDV PI animals resulted in substantial costs attributable to negative effects on performance and increased fatalities.

Full access
in American Journal of Veterinary Research

SUMMARY

Biological responses to recombinant dna-derived bovine interferon α (rBoifn-αI1) by bovine alveolar macrophages were examined by measuring viral yield reduction and 2′,5′-oligoadenylate synthetase (2′,5′-oas) production by ifn-treated cells. In vitro ifn pretreatment of alveolar macrophages reduced viral yield in cultures challenged exposed with parainfluenza-3 virus, compared with control cultures. In vitro treatment of alveolar macrophages with ifn also resulted in increased 2′,5′-oas activity. The 2′,5′-oas activity was measured in alveolar macrophages and blood mononuclear leukocytes of calves injected im with 3.6 × 106 U of rBoifn-αI1/kg of body weight. The ifn action was monitored by measuring 2′,5′-oas activity of blood mononuclear leukocytes beginning 6 days before and ending 24 hours after ifn treatment. The 2′,5′-oas activity in the blood mononuclear leukocytes sharply increased 24 hours after ifn treatment, indicating response to ifn. The alveolar macrophages collected from the same calves 24 hours after ifn administration also had increased 2′,5′-oas activity, compared with alveolar macrophages from the same calves collected 6 days before treatment. Increased 2′,5′-oas activity indicates: a possible mechanism of ifn action in cattle that may be responsible for viral yield reduction; potential use of high enzyme activity as a marker for ifn induction; and potential use of 2′,5′-oas activity as a marker for determining effects of ifn on bovine macrophages and other cells of the bovine immune system.

Free access
in American Journal of Veterinary Research

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 detect bovine adenovirus serotype 7 (BAV-7) infections in calves by use of viral isolation and serologic testing.

Animals—205 postweaning calves.

Procedure—121 calves were assembled by an order buyer through auction markets in eastern Tennessee and transported to New Mexico where they were commingled with 84 healthy ranch-reared calves. Tests included viral isolation in cell culture from peripheral blood leukocytes (PBL) and detection of serum BAV-7 antibodies by use of microtitration viral neutralization.

Results —BAV-7 was isolated from PBL of 8 calves and seroconversion to BAV-7 was detected for 38 of 199 (19.1%) calves. Concurrent bovine viral diarrhea virus infections were detected in most calves from which BAV-7 was isolated.

Conclusions and Clinical Relevance —Results of our study indicate that BAV-7 infections can be found in postweaning commingled calves and may develop more commonly in calves with concurrent infections with viruses such as bovine viral diarrhea virus (BVDV). (Am J Vet Res 2002;63:976–978).

Full access
in American Journal of Veterinary Research

SUMMARY

Administration of an N-lauroylsarcosine-derived outer membrane protein fraction of Pasteurella haemolytica A1 (sci-1) induced a protective response in calves against intrathoracic challenge exposure with the homologous serovar. Outer membrane proteins from heterologous serovars, A6 and A9, induced partial protection that was associated with their respective similarities to serovar A1 in outer membrane protein profiles derived by use of sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Calves vaccinated with sci preparations did not have detectable neutralizing antibody to P haemolytica A1 leukotoxin. Antibodies to whole-cell antigens, carbohydrate-protein subunit antigen, and sci-1 were associated with resistance, which indicates that protein antigens shared among cell surface, carbohydrate-protein subunit, and sci preparations are immunogenic and enhance resistance to experimental challenge exposure.

Free access
in American Journal of Veterinary Research