Objective—To determine whether serologic evaluation
of 5 unvaccinated 6- to 12-month-old heifers is a
valid method for identifying herds that contain cattle
persistently infected (PI) with bovine viral diarrhea
Animals—14 dairy herds with a history of BVDV
infection, with health problems consistent with BVDV
infection, or at risk for contracting BVDV infection.
Procedure—5 unvaccinated 6- to 12-month-old
heifers were randomly selected from each herd.
Neutralizing antibody titers for type-I and -II BVDV
were determined. A herd was classified as likely to
contain PI cattle when at least 3/5 heifers had antibody
titers ≥ 128. Virus isolation was performed on all
cattle to identify PI cattle. Genotype of isolated viruses
was determined by nested multiplex polymerase
Results—6 of 14 herds contained PI cattle.
Sensitivity and specificity of serologic evaluation of
5 heifers for identifying these herds were 66 and
100%, respectively. In herds that contained PI cattle,
the predominant BVDV titer in the tested
heifers corresponded to the genotype of the isolated
Conclusions and Clinical Relevance—Serologic
evaluation of unvaccinated 6- to 12- month-old heifers
is an accurate method for identifying herds containing
PI cattle. Both type-I and -II BVDV antibody titers
should be determined to prevent herd misclassification.
The genotype of BVDV found in PI cattle can be
predicted by the predominant neutralizing antibody
titers found in tested heifers. Serologic evaluation of
5 unvaccinated heifers can be used to determine
whether a herd is likely to contain PI cattle.
(Am J Vet Res 2002;63:499–505)
Objective—To determine whether vaccine virus can be detected by use of reverse transcriptase (RT)-PCR assays for pooled and individual skin samples obtained from cattle after vaccination with a commercially available modified-live bovine viral diarrhea virus (BVDV) vaccine.
Animals—12 BVDV-seropositive steer calves and 7 BVDV-seronegative (antibody titer < 1:4) heifers; all cattle were free of persistent infection with BVDV.
Procedures—2 experiments were conducted. Cattle were vaccinated on day 0 with a commercially available modified-live BVDV vaccine. Skin samples were collected on days 0, 3 to 14, 16, and 18 for virus detection by use of RT-PCR assay on individual and pooled samples. In addition, blood samples and nasal swab specimens were collected for virus isolation.
Results—All cattle, regardless of serologic status, had negative results for BVDV as determined by use of RT-PCR assay of individual and pooled skin samples. Virus was detected via virus isolation in serum or the buffy coat in 5 of 7 heifers that were seronegative when vaccinated.
Conclusions and Clinical Relevance—These findings indicated that it would be unlikely to detect BVDV vaccine virus in skin by use of RT-PCR assay of individual or pooled skin samples obtained from cattle after vaccination with a commercially available modified-live BVDV vaccine. Veterinarians and producers should be confident that positive test results for BVDV on skin samples would not likely be caused by the vaccination virus after administration of a modified-live virus vaccine.
Objective—To evaluate 2 rapid, patient-side assays
for detection of Cryptosporidium parvum in feces
from neonatal calves with diarrhea.
Design—Diagnostic test evaluation.
Sample Population—Fecal samples from 96 neonatal
(1 to 30 days old) calves with diarrhea.
Procedure—Results of the rapid assays were compared
with results of microscopic examination of fecal smears
that had been stained with diamant fuchsin stain.
Results—One of the rapid assays correctly identified
56 of 62 (90%) fecal samples positive for C parvum
oocysts and 33 of 34 (97%) fecal samples negative
for oocysts. The other assay correctly identified 53 of
62 (85%) fecal samples positive for oocysts and 33 of
34 (97%) fecal samples negative for oocysts.
Conclusions and Clinical Relevance—Results suggest
that these 2 rapid assays are accurate when
used to detect C parvum in fecal samples from
neonatal calves with diarrhea. ( J Am Vet Med Assoc 2004;225:1090–1092)
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 estimate herd-level sensitivity (HSe),
specificity (HSp), and predictive values for a positive
(HPVP) and negative (HPVN) test result for several
testing scenarios for detection of tuberculosis in cattle
by use of simulation modeling.
Sample Population—Empirical distributions of all
herds (15,468) and herds in a 10-county area (1,016) in
Procedures—5 test scenarios were simulated: scenario
1, serial interpretation of the caudal fold tuberculin
(CFT) test and comparative cervical test (CCT);
scenario 2, serial interpretation of the CFT test and
CCT, microbial culture for mycobacteria, and polymerase
chain reaction assay; scenario 3, same as scenario
2 but specificity was fixed at 1.0; and scenario 4,
sensitivity was 0.9 (scenario 4a) or 0.95 (scenario 4b),
and specificity was fixed at 1.0.
Results—Estimates for HSe were reasonably high,
ranging between 0.712 and 0.840. Estimates for HSp
were low when specificity was not fixed at 1.0.
Estimates of HPVP were low for scenarios 1 and 2
(0.042 and 0.143, respectively) but increased to 1.0
when specificity was fixed at 1.0. The HPVN remained
high for all 5 scenarios, ranging between 0.995 and
0.997. As herd size increased, HSe increased and HSp
and HPVP decreased. However, fixing specificity at
1.0 had only minor effects on HSp and HPVN, but HSe
was low when the herd size was small.
Conclusions and Clinical Relevance—Tests used
for detecting cattle herds infected with tuberculosis
work well on a herd basis. Herds with < approximately
100 cattle should be tested more frequently or for
a longer duration than larger herds to ensure that
these small herds are free of tuberculosis. (Am J Vet
Objective—To evaluate the efficacy of a commercially available killed bovine viral diarrhea virus (BVDV) vaccine to protect against fetal infection in pregnant cattle continually exposed to cattle persistently infected with the BVDV.
Animals—60 crossbred beef heifers and 4 cows persistently infected with BVDV.
Procedures—Beef heifers were allocated to 2 groups. One group was vaccinated twice (21-day interval between the initial and booster vaccinations) with a commercially available vaccine against BVDV, and the other group served as nonvaccinated control cattle. Estrus was induced, and the heifers were bred. Pregnancy was confirmed by transrectal palpation. Four cows persistently infected with BVDV were housed with 30 pregnant heifers (15 each from the vaccinated and nonvaccinated groups) from day 52 to 150 of gestation. Fetuses were then harvested by cesarean section and tested for evidence of BVDV infection.
Results—1 control heifer aborted after introduction of the persistently infected cows. Bovine viral diarrhea virus was isolated from 14 of 14 fetuses obtained via cesarean section from control heifers but from only 4 of 15 fetuses obtained via cesarean section from vaccinated heifers; these proportions differed significantly.
Conclusions and Clinical Relevance—A commercially available multivalent vaccine containing an inactivated BVDV fraction significantly reduced the risk of fetal infection with BVDV in heifers continually exposed to cattle persistently infected with BVDV. However, not all vaccinated cattle were protected, which emphasizes the need for biosecurity measures and elimination of cattle persistently infected with BVDV in addition to vaccination within a herd.
Procedures—Weaned calves were or were not vaccinated against BVDV at feedlot arrival (trial 1) or 2 (trial 2) or 3 (trial 3) weeks before feedlot arrival. During trial 1, half of the calves were commingled with PI cattle throughout the feeding period. During trial 2, 63 calves were exposed to PI cattle before weaning and all calves were exposed to PI cattle throughout the feeding period. During trial 3, all study calves were exposed to PI cattle throughout the feeding period. Morbidity and mortality rates and average daily gain (ADG) data were analyzed.
Results—During trial 1, calves maintained with PI cattle had a higher morbidity rate regardless of BVDV vaccination than did calves not exposed to PI cattle; however, for calves maintained with PI cattle, the morbidity rate for those vaccinated against BVDV was less than that for those not vaccinated against BVDV. During trial 2, calves exposed to PI cattle before weaning or vaccinated against BVDV had lower morbidity and mortality rates and increased ADG, compared with those for calves not exposed to PI cattle before weaning or vaccinated against BVDV. During trial 3, health and performance did not vary between calves that were and were not vaccinated against BVDV.
Conclusions and Clinical Relevance—Exposure of cattle to BVDV naturally or through vaccination before or at feedlot arrival mitigated the negative effects of constant exposure to PI cattle.
Objective—To determine whether an interferon (IFN)-γ response sufficient to categorize cattle as positive for tuberculosis can be detected in blood collected at commencement of exsanguination at slaughter.
Animals—15 Holstein cows.
Procedures—12 cows were experimentally sensitized by SC injection with inactivated Mycobacterium bovis in mineral oil, which induced an immune response that mimicked natural infection with M bovis. Three nonsensitized control cows were injected SC with mineral oil alone. By 5 weeks after injection, only the 12 sensitized cows had positive results for tuberculosis with whole blood IFN-γ assay. At that time, all 15 cows were sent to slaughter and samples of blood were collected from each cow immediately before stunning and at commencement of exsanguination (within 90 seconds after stunning). A whole blood IFN-γ assay was performed on the samples. Conditional probability and paired t tests were used to analyze changes in the categorical test interpretation and qualitative IFN-γ production, respectively.
Results—All 12 sensitized cows had positive results for tuberculosis in samples obtained immediately before stunning, and 9 retained positive results for samples obtained at commencement of exsanguination. There was a significant decrease in the mean background-corrected IFN-γ ELISA optical density values for samples obtained at commencement of exsanguination.
Conclusions and Clinical Relevance—IFN-γ response sufficient to classify cattle as positive for tuberculosis could be detected in blood collected at commencement of exsanguination. These findings support further development and use of the IFN-γ assay on blood samples collected at exsanguination as part of a bovine tuberculosis surveillance program.
OBJECTIVE To determine whether Mycobacterium bovis remains viable in ensiled forages.
SAMPLE Alfalfa, mixed mostly grass, and corn silages.
PROCEDURES For each of 10 sampling days, six 250-g replicate samples of each feedstuff were created and placed in a film pouch that could be vacuum sealed to simulate the ensiling process. Within each set of replicate samples, 4 were inoculated with 10 mL of mycobacterial liquid culture medium containing viable M bovis and 2 were inoculated with 10 mL of sterile mycobacterial liquid culture medium (controls) on day 0. Pouches were vacuum sealed and stored in the dark at room temperature. On the designated sampling day, 1 control pouch was submitted for forage analysis, and the other pouches were opened, and forage samples were obtained for M bovis culture and analysis with a PCR assay immediately and 24 hours later.
RESULTS None of the control samples had positive M bovis culture or PCR assay results. Among M bovis-inoculated samples, the organism was not cultured from alfalfa and corn silage for > 2 days but was cultured from mixed mostly grass silage for 28 days after inoculation and ensiling initiation. Mycobacterium bovis DNA was detected by PCR assay in samples of all 3 feedstuffs throughout the 112-day observation period.
CONCLUSIONS AND CLINICAL RELEVANCE Results suggested that properly ensiled forages would be an unlikely source for M bovis transmission to cattle. Further research is necessary to determine whether ensiling kills M bovis or forces it to become dormant and, if the latter, elucidate the conditions that cause it to revert to an infectious state.
The subclinical impact of bovine leukemia virus (BLV) on the sustainability of the US dairy industry is only now being fully recognized. Findings of recent longitudinal studies conducted in Michigan dairy herds were consistent with the results of previous studies in showing that within-herd prevalence of BLV–infected cattle was negatively associated with milk production and cow longevity. Risk factors relating to routes of hematogenous transmission such as the use of shared hypodermic needles, shared reproductive examination sleeves, and natural breeding were associated with BLV within-herd prevalence. Few US dairy producers know the prevalence of BLV-infected cattle in their herds or are aware of the insidious economic impact of BLV or the options for BLV control. As an increasing number of countries eradicate BLV from their cattle populations, restrictions on the movement of US cattle and cattle products will likely increase. Veterinarians should be aware of recent developments for screening serum and milk samples for antibodies against BLV and the results of research regarding the economic impact of BLV so they can advise their dairy clients of available alternatives for monitoring and controlling BLV infection.