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  • Author or Editor: Steven B. Kleiboeker x
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Abstract

Objective—To determine the interval to provirus and serum antibody detection (via PCR assay and ELISA, respectively) in calves after experimental inoculation with bovine leukemia virus (BLV).

Animals—8 colostrum-deprived, BLV-negative Holstein bull calves (≥ 6 weeks old).

Procedures—Via IM injection, each calf received a fresh whole-blood inoculum (day 0) calculated to contain 2 × 106 lymphocytes. Blood samples for the ELISA and PCR assay were collected from calves immediately prior to inoculation and weekly thereafter for 7 weeks. Mean and median number of weeks to PCR-detected conversion of BLV status and seroconversion were calculated. Point sensitivity and cumulative sensitivity of the 2 assays were calculated at each sample collection. At each sampling time, the proportion of calves identified as infected by the cumulative weekly ELISA and PCR assay results was compared by use of a Fisher exact test.

Results—In 5 calves, conversion of BLV status was detected via PCR assay before seroconversion was identified. However, seroconversion preceded PCR-detected conversion in 2 calves. In 1 calf, both assays yielded positive results at the same test date. These differences were not significant.

Conclusions and Clinical Relevance—In experimentally inoculated BLV-negative calves, conversion of BLV status was detected via PCR assay more quickly than via ELISA; this difference was not significant and probably not clinically important. The PCR assay may be useful as a confirmatory test in animals of exceptional value; tests based on viral identification may become critically important if vaccines against BLV infection are developed and marketed.

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine whether bovine herpesvirus 1 (BHV1), bovine viral diarrhea (BVDV) virus 1 (BVDV1), or BVDV 2 (BVDV2) were shed after parenteral administration of a multivalent modified-live virus vaccine.

Design—Prospective study.

Animals—28 healthy beef calves and 4 healthy pregnant beef cows.

Procedure—A commercially available modified-live virus multivalent vaccine was administered to steers and heifers (n = 18) that were seronegative to BHV1, BVDV1, and BVDV2. Four seronegative pregnant control cows were held in contact with the vaccinated calves for 103 days. Unvaccinated calves (n = 10) were held as controls in a separate double-fenced pen. Seroconversion was monitored by determining serum neutralization titers after vaccination. Viral shedding and viremia were assessed via analysis of nasal swab specimens and blood by use of polymerase chain reaction (PCR) and reverse transcriptase-PCR assays and virus isolation.

Results—A transient BVDV1 viremia was detected in most vaccinated calves 3 to 10 days after vaccination. All vaccinated calves seroconverted to BVDV1 and BVDV2. Seventeen of 18 vaccinated calves seroconverted to BHV1. Viral shedding was not detected in the vaccinated calves. All control cattle remained seronegative to BHV1, BVDV1, and BVDV2 throughout the study.

Conclusions and Clinical Relevance—Shedding of BHV1, BVDV1, and BVDV2 after vaccination was either nonexistent or undetected and did not result in transmission of BHV1, BVDV1, or BVDV2 vaccine viruses to pregnant contact control cows. (J Am Vet Med Assoc 2003;222:1399–1403)

Full access
in Journal of the American Veterinary Medical Association

Abstract

Objective—To evaluate the use of a polymerase chain reaction (PCR) assay in detecting bovine leukosis virus (BLV) in adult dairy cows.

Design—Prospective study.

Animals—223 adult dairy cows.

Procedure—Cows were tested for BLV status by use of an ELISA and a PCR assay. Sensitivity, specificity, predictive values of positive and negative tests, and the percentage of cows correctly classified by PCR assay were calculated. Ninety-five percent confidence intervals were calculated for sensitivity and specificity.

Results—Sensitivity and specificity were 0.672 and 1.00, respectively. Prevalence of BLV in this herd was 0.807. Predictive value of a positive test was 1.00, and predictive value of a negative test was 0.421. The percentage of cows correctly classified by PCR assay was 73.5%.

Conclusions and Clinical Relevance—A positive PCR assay result provided definitive evidence that a cow was infected with BLV. Sensitivity and negative predictive value for PCR assay were low. Consequently, PCR assay alone is unreliable for routine detection of BLV in herds with high prevalence of the disease. (J Am Vet Med Assoc 2003;222:983–985)

Full access
in Journal of the American Veterinary Medical Association

Abstract

Objective—To determine whether strength of serologic recognition of bovine leukosis virus (BLV) by use of ELISA is associated with blood lymphocyte counts.

Design—Prospective study.

Animals—161 cows with positive results of ELISA for BLV.

Procedure—Sample-to-positive ratio (S:P), which is the ratio between the test sample and a positive control sample, was compared among lymphocytotic and nonlymphocytotic cows. A regression model was constructed to evaluate the association between blood lymphocyte concentration and S:P, age, and the interaction of these terms.

Results—Mean S:P differed significantly between lymphocytotic (2.58 ± 0.36) and nonlymphocytotic (2.38 ± 0.39) cows. Age and S:P were significantly associated with lymphocyte count.

Conclusions and Clinical Relevance—Sample-topositive ratio and lymphocyte count were related; however, cows with high S:P were not always lymphocytotic. Culling cows on the basis of S:P will reduce the herd load of infectious virus faster than random culling of ELISA-positive cows; however, culling on the basis of lymphocyte count will eliminate a greater proportion of the reservoir of infection. (J Am Vet Med Assoc 2002;220:1681–1684)

Full access
in Journal of the American Veterinary Medical Association

Abstract

Objective—To evaluate retention of porcine reproductive and respiratory syndrome virus (PRRSV) in houseflies for various time frames and temperatures.

Sample Population—Fifteen 2-week-old pigs, two 10-week-old pigs, and laboratory-cultivated houseflies.

Procedure—In an initial experiment, houseflies were exposed to PRRSV; housed at 15°, 20°, 25°, and 30°C; and tested at various time points. In a second experiment to determine dynamics of virus retention, houseflies were exposed to PRRSV and housed under controlled field conditions for 48 hours. Changes in the percentage of PRRSV-positive flies and virus load per fly were assessed over time, and detection of infective virus at 48 hours after exposure was measured. Finally, in a third experiment, virus loads were measured in houseflies allowed to feed on blood, oropharyngeal washings, and nasal washings obtained from experimentally infected pigs.

Results—In experiment 1, PRRSV retention in houseflies was proportional to temperature. In the second experiment, the percentage of PRRSV-positive houseflies and virus load per fly decreased over time; however, infective PRRSV was found in houseflies 48 hours after exposure. In experiment 3, PRRSV was detected in houseflies allowed to feed on all 3 porcine body fluids.

Conclusions and Clinical Relevance—For the conditions of this study, houseflies did not support PRRSV replication. Therefore, retention of PRRSV in houseflies appears to be a function of initial virus load after ingestion and environmental temperature. These factors may impact the risk of insect-borne spread of PRRSV among farms. (Am J Vet Res 2005;66:1517–1525)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine the effect of dietary supplemental lipoic acid (LA) on serum concentrations of metabolic hormones and acute-phase proteins of steers challenged with infectious bovine rhinotracheitis virus (IBRV).

Animals—32 steers.

Procedures—Steers were randomly assigned to 4 treatments: negative control (NC; no LA, no IBRV challenge), control (CON; no LA, IBRV challenge), 16 mg of LA/kg of body weight (BW)/d plus IBRV challenge (LA16), and 32 mg of LA/kg of BW/d plus IBRV challenge (LA32). Following a 21-day adaptation period, CON, LA16, and LA32 steers received IBRV (2 mL/nostril [day 0]); NC steers received saline (0.9% NaCl) solution. Blood samples, nasal swab specimens, BW, and rectal temperatures were obtained 0, 1, 3, 5, 7, 14, and 21 days after challenge. Serum was analyzed for concentrations of haptoglobin, amyloid-A, leptin, and anti-IBRV antibodies.

Results—Steers fed LA32 began gaining BW by day 7, whereas BW of CON and LA16 steers declined. Serum haptoglobin concentration of LA32 steers was lower than that of CON and LA16 steers on day 7. Serum neutralization titers for 30 of 32 steers were negative for anti-IBRV antibodies before challenge; however, all steers (including NCs) had antibodies on day 21.

Conclusions and Clinical Relevance—Results suggested that LA supplementation augmented certain aspects of the immune response; LA32 steers had a more rapid recovery from IBRV viral challenge than did others.

Full access
in American Journal of Veterinary Research