Objective—To examine the role of bovine viral diarrhea
virus (BVDV) biotype on the establishment of
fetal infection in cattle.
Animals—30 mixed-breed pregnant cows.
Procedure—Pregnant cows were inoculated
oronasally with either i-VVNADL, originating from an
infectious BVDV cDNA clone of the National Animal
Disease Laboratory (NADL) isolate, or the parental
virus stock, termed NADL-A.
Results—All cows developed neutralizing antibodies
to BVDV, and virus was commonly isolated from
peripheral blood mononuclear cells or nasal swab
specimens of NADL-A inoculated cows; however,
virus was rarely isolated from specimens of i-VVNADL
inoculated cows. i-VVNADL did not cause fetal infection,
whereas all fetuses harvested from NADL-A
inoculated cows at 6 weeks after inoculation had evidence
of infection. Immunoblot analysis of fetal virus
isolates revealed the absence of NS3, confirming a
noncytopathic (NCP) biotype BVDV in the NADL-A
stock. The sequence of the NCP contaminant (termed
NADL-1102) and the i-VVNADL genome were virtually
identical, with the exception of a 270 nucleotide-long
insert in the i-VVNADL genome. Phylogenetic analyses
revealed that NADL-1102 forms a monophyletic
group with 6 other NADL genomes.
Conclusions and Clinical Relevance—These data
suggest that the contaminating NCP virus in the
NADL-A stock was the ancestral NADL virus, which
originally infected a bovine fetus and recombined to
produce a cytopathic (CP) variant. Following oronasal
infection of pregnant cows, viremia and transplacental
transmission of CP BVDV to the fetus is rare, compared
with the high occurrence of maternal viremia
and fetal infection observed with NCP BVDV.
(Am J Vet Res 2002;63:1455–1463)
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.
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.