Objective—To determine whether cattle persistently
infected with bovine viral diarrhea virus (BVDV) that
lack virus detectable in serum by use of the
immunoperoxidase microtiter assay (IPMA) can transmit
the virus to susceptible herdmates and determine
prevalence of these cattle.
Design—Clinical trial and serologic survey.
Sample Population—2 cattle and 1,952 blood samples.
Procedure—A persistently infected cow in which
virus could not be detected in serum was housed
with a BVDV-seronegative steer. Blood and nasal
swab specimens were tested via virus isolation and
serum virus neutralization. Parallel WBC preparations
and sera from blood samples of 1,952 adult cows
were screened for BVDV by use of IPMA.
Results—The steer seroconverted to BVDV within 4
weeks of contact with the cow. Virus was detected in
sera and WBC of 5 adult cows that were verified as
persistently infected by retest 3 weeks later. Cattle
persistently infected with BVDV in which virus could
not be detected in both serum and WBC by use of
IPMA were not found.
Conclusion and Clinical Relevance—Cattle persistently
infected with BVDV in which virus cannot be
detected in serum by use of IPMA may serve as virus
reservoirs for infecting susceptible cattle. Persistent
infection was detected at a prevalence of 0.26%.
Screening adult cattle by use of IPMA on serum samples
appears to be a reliable means of detecting persistent
infection with BVDV. Prevalence of cattle persistently
infected with BVDV that have negative
results of IPMA on serum is extremely low. (J Am Vet
Med Assoc 2001;219:629–631)
Objective—To evaluate onset of protection induced by modified-live virus (MLV) bovine viral diarrhea virus (BVDV) vaccine administered 7, 5, or 3 days before inoculation with type 1b BVDV (strain NY-1).
Procedures—Calves were assigned to 4 groups: an unvaccinated control group or groups vaccinated with MLV vaccine containing BVDV types 1a and 2 at 7, 5, or 3 days, before inoculation with NY-1 BVDV. Blood samples were collected for leukocyte counts, serum virus neutralization, and virus isolation (VI); nasal swab specimens (NSSs) were obtained for VI, and rectal temperatures were monitored for 14 days after inoculation.
Results—No significant differences in leukocyte counts or rectal temperatures were detected after BVDV inoculation in vaccinated calves. Vaccinated calves had reduced viremia and viral shedding after inoculation, compared with results for unvaccinated calves. On day 5 after inoculation, a higher proportion of calves vaccinated 3 days before inoculation had positive VI from NSSs, compared with NSS VI results for calves vaccinated 5 and 7 days before inoculation. Unvaccinated calves had leukopenia on days 3, 5, and 6 and had higher rectal temperatures on days 7 and 8 after inoculation, compared with temperatures before inoculation. All unvaccinated calves had ≥ 1 positive VI result from NSSs 3 to 11 days after inoculation, and 4 became viremic.
Conclusions and Clinical Relevance—MLV BVDV vaccine prevented fever, viremia, and leukopenia in calves challenge inoculated with NY-1 BVDV. A high proportion of calves vaccinated 3 days before inoculation shed BVDV after inoculation.
OBJECTIVE To assess the use of 3-D accelerometers to evaluate behavioral changes in cattle experimentally infected with a low-virulent strain of bovine viral diarrhea virus (BVDV).
ANIMALS 20 beef steers (mean weight, 238 kg).
PROCEDURES Calves were allocated to a BVDV (n = 10) or control (10) group. On day 0, calves in the BVDV group were inoculated with a low-virulent strain of BVDV (4 × 106 TCID50, intranasally), and calves in the control group were sham inoculated with BVDV-free medium (4 mL; intranasally). An accelerometer was affixed to the right hind limb of each calf on day −7 to record activity (lying, walking, and standing) continuously until 35 days after inoculation. Baseline was defined as days −7 to −1. Blood samples were collected at predetermined times for CBC, serum biochemical analysis, virus isolation, and determination of anti-BVDV antibody titers.
RESULTS All calves in the BVDV group developed viremia and anti-BVDV antibodies but developed only subclinical or mild disease. Calves in the control group did not develop viremia or anti-BVDV antibodies. Mean time allocated to each activity did not differ significantly between the BVDV and control groups on any day except day 8, when calves in the BVDV group spent less time standing than the calves in the control group. Following inoculation, calves in both groups tended to spend more time lying and less time walking and standing than they did during baseline.
CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that behavioral data obtained by accelerometers could not distinguish calves subclinically infected with BVDV from healthy control calves. However, subtle changes in the behavior of the BVDV-infected calves were detected and warrant further investigation.
OBJECTIVE To determine titers of serum antibodies against 3 genotypes of bovine parainfluenza 3 virus (BPI3V) in unvaccinated ungulates in Alabama.
ANIMALS 62 cattle, goats, and New World camelids from 5 distinct herds and 21 captured white-tailed deer.
PROCEDURES Serum samples were obtained from all animals for determination of anti-BPI3V antibody titers, which were measured by virus neutralization assays that used indicator (reference) viruses from each of the 3 BPI3V genotypes (BPI3V-A, BPI3V-B, and BPI3V-C). The reference strains were recent clinical isolates from US cattle. Each sample was assayed in triplicate for each genotype. Animals with a mean antibody titer ≤ 2 for a particular genotype were considered seronegative for that genotype.
RESULTS Animals seropositive for antibodies against BPI3V were identified in 2 of 3 groups of cattle and the group of New World camelids. The geometric mean antibody titer against BPI3V-B was significantly greater than that for BPI3V-A and BPI3V-C in all 3 groups. All goats, captive white-tailed deer, and cattle in the third cattle group were seronegative for all 3 genotypes of the virus.
CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that BPI3V-A may no longer be the predominant genotype circulating among ungulates in Alabama. This may be clinically relevant because BPI3V is frequently involved in the pathogenesis of bovine respiratory disease complex, current vaccines contain antigens against BPI3V-A only, and the extent of cross-protection among antibodies against the various BPI3V genotypes is unknown.
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
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
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. (Am J Vet Res 2005;66:1738–1742)
OBJECTIVE To evaluate the efficacy of 4 commercially available multivalent modified-live virus vaccines against clinical disease, viremia, and viral shedding caused by bovine viral diarrhea virus (BVDV) and bovine herpesvirus 1 (BHV1) in early-weaned beef calves.
PROCEDURES Calves were randomly assigned to 1 of 5 groups and administered PBSS (group A [control]; n = 11) or 1 of 4 commercially available modified-live virus vaccines that contained antigens against BHV1, BVDV types 1 (BVDV1) and 2 (BVDV2), parainfluenza type 3 virus, and bovine respiratory syncytial virus (groups B , C , D , and E ). Forty-five days after vaccination, calves were exposed simultaneously to 6 cattle persistently infected with BVDV and 8 calves acutely infected with BHV1 for 28 days (challenge exposure). For each calf, serum antibody titers against BVDV and BHV1 were determined before vaccination and before and after challenge exposure. Virus isolation was performed on nasal secretions, serum, and WBCs at predetermined times during the 28-day challenge exposure.
RESULTS None of the calves developed severe clinical disease or died. Mean serum anti-BHV1 antibody titers did not differ significantly among the treatment groups at any time and gradually declined during the study. Mean serum anti-BVDV antibody titers appeared to be negatively associated with the incidence of viremia and BVDV shedding. The unvaccinated group (A) had the lowest mean serum anti-BVDV antibody titers. The mean serum anti-BVDV antibody titers for group D were generally lower than those for groups B, C, and E.
CONCLUSIONS AND CLINICAL RELEVANCE Results indicated differences in vaccine efficacy for the prevention of BVDV viremia and shedding in early-weaned beef calves.
Objective—To compare degree of viremia and disease
manifestations in calves with type-I and -II
bovine viral diarrhea virus (BVDV) infection.
Procedure—Colostrum-deprived calves obtained
immediately after birth were assigned to 1 control
and 3 treatment groups (4 calves/group). Calves in
treatment groups were inoculated (day 0) by
intranasal instillation of 107 median tissue culture
infective dose BVDV 890 (type II), BVDV 7937 (type
II), or BVDV TGAN (type I). Blood cell counts and virus
isolation from serum and leukocytes were performed
daily, whereas degree of viremia was determined
immediately before and 4, 6, 8, and 12 days after
inoculation. Calves were euthanatized on day 12, and
pathologic, virologic, and immunohistochemical
examinations were performed.
Results—Type-II BVDV 890 induced the highest
degree of viremia, and type-I BVDV TGAN induced
the lowest. Virus was isolated more frequently and
for a longer duration in calves inoculated with BVDV
890. A parallel relationship between degree of viremia
and rectal temperature and an inverse relationship
between degree of viremia and blood cell counts was
observed. Pathologic and immunohistochemical
examinations revealed more pronounced lesions and
more extensive distribution of viral antigen in calves
inoculated with type-II BVDV.
Conclusions and Clinical Relevance—Degree of
viremia induced during BVDV infection is associated
with severity of clinical disease. Isolates of BVDV that
induce a high degree of viremia may be more capable
of inducing clinical signs of disease. Strategies (eg,
vaccination) that reduce viremia may control clinical
signs of acute infection with BVDV. (Am J Vet Res