Severe disease following experimental exposure of calves to noncytopathic bovine viral diarrhoea virus isolate New York-1

Platelet function and association of bovine viral diarrhea virus with platelets of persistently infected cattle

OBJECTIVE

To determine whether viral involvement with platelets obtained from cattle persistently infected (PI) with bovine viral diarrhea virus (BVDV) is associated with altered platelet function or decreased platelet counts.

SAMPLE POPULATION

Platelets obtained from 8 cattle PI with BVDV and 6 age-, sex-, and breed-matched uninfected control cattle.

PROCEDURE

Manual platelet counts were determined, and platelet function was assessed through optical aggregometry by use of the aggregation agonists ADP and platelet-activating factor. Identification of BVDV in serum and preparations of purified platelets was determined by use of virus isolation tests.

RESULTS

No significant difference in platelet counts was detected between cattle PI with BVDV and control cattle. In response to the aggregation agonists, maximum aggregation percentage and slope of the aggregation curve were not significantly different between cattle PI with BVDV and control cattle. We isolated BVDV from serum of all PI cattle and from purified platelets of 6 of 8 PI cattle, but BVDV was not isolated from serum or platelets of control cattle.

CONCLUSIONS AND CLINICAL RELEVANCE

Isolation of BVDV from platelets in the peripheral circulation of cattle immunotolerant to BVDV does not result in altered platelet function or decreases in platelet counts.

Bovine viral diarrhea virus with deletions in the 5'-nontranslated region: reduction of replication in calves and induction of protective immunity

Bovine viral diarrhea virus (BVDV) with deletions in the 5'-nontranslated region (5'-NTR) were tested for their suitability as live BVD vaccines. Firstly, the genetic stability of the mutants was established by culturing over 15 passages in bovine cells. Secondly, two deletion mutants and the parent strain CP7-5A were characterised with respect to in vivo replication competence, attenuation and induction of protective immunity against BVDV. Naïve calves (n = 5 per group) were inoculated with mutants d2-31 and d5-57 or CP7-5A and 5 weeks later, a challenge with the BVDV type 1 strain New York was performed. The mutants were found to be genetically and phenotypically stable. Moreover, the results indicate that the mutants were attenuated with regard to effects including pyrexia and drop in leucocyte counts. Infection with the mutants induced moderate to high titers of BVDV neutralizing antibodies and completely prevented viremia after challenge infection with a heterologous BVDV strain. Taken together, the 5'-NTR deletion mutants combine a good safety profile with good efficacy and are therefore well suited as candidate live vaccines.