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SUMMARY

Colostrum-deprived calves (n = 24) were fed various amounts of colostrum, colostrum substitute, or milk replacer to establish a range in titer of passively acquired viral neutralizing antibody in serum. The calves were then challenge exposed intranasally with a virulent, noncytopathic bovine viral diarrhea virus (bvdv-890). After viral challenge exposure, calves were monitored for fever, leukopenia, thrombocytopenia, and diarrhea. In addition, viral isolation and viral titration were performed on specimens of nasal secretions, buffy coat cells, and serum obtained from the calves. Fever and systemic spread of virus were detected in calves that had viral neutralizing titer of 256 or lower. Calves that had viral neutralizing titer lower than 16 developed severe clinical disease manifested by fever, leukopenia, thrombocytopenia, and diarrhea. Severity and duration of signs of disease decreased as titers of passively acquired viral neutralizing antibody increased. These results indicate that low to intermediate titers of passively acquired viral neutralizing antibody were not sufficient to fully protect calves from virulent bovine viral diarrhea virus.

Free access
in American Journal of Veterinary Research

Summary

A noncytopathic bovine viral diarrhea virus (bvdv), bvdv-890, isolated from a yearling heifer that died with extensive internal hemorrhages, was compared for virulence in calves with noncytopathic bvdv-TGAN, isolated from an apparently healthy persistently infected calf. After challenge exposure with bvdv-890, nonimmune calves (n = 7) developed fever > 40 C, diarrhea, leukopenia, lymphopenia, neutropenia, and thrombocytopenia. Most calves (n = 6) died or were euthanatized by 19 days after challenge exposure. Challenge exposure with bvdv-890 did not induce disease in 2 calves that had congenital persistent infection with bvdv or in 3 calves that had neutralizing antibody titer > 4 against bvdv-890. After challenge exposure with bvdv-TGAN, nonimmune calves (n = 7) developed fever > 40 C and, rarely, diarrhea or lymphopenia. All of those calves survived challenge exposure. The average maximal titer of bvdv-890 isolated from serum was 1,000 times that of bvdv-TGAN. In calves infected with bvdv-890, the average maximal percentages of lymphocytes and platelets associated with virus were greater than those found in calves infected with bvdv-TGAN. Additional findings of epidemiologic significance were prolonged shedding of virus and delayed production of viral-neutralizing antibody in 1 calf challenge-exposed with bvdv-890. Also, after production of neutralizing antibody, mutant virus that was refractory to neutralization was isolated from calves challenge-exposed with bvdv-TGAN.

Free access
in American Journal of Veterinary Research

SUMMARY

Enriched populations of neutrophils and mononuclear leukocytes from 9 cattle persistently infected with non-cytopathic bovine viral diarrhea virus were analyzed for frequency of association with virus, using flow cytometric procedures. Trypsinization of neutrophils decreased the frequency of viral association from 0.82% to 0.49%. Similar treatment of mononuclear leukocytes decreased the frequency of viral association from 5.53% to 4.81%. Results of immunocytochemical procedures to locate viral antigen were inconclusive for neutrophils, but viral antigen was found in the cytoplasm of mononuclear leukocytes. A distinct and highly pure population of eosinophils was identified during flow cytometric analysis of neutrophil populations from 2 of 9 cattle.

Free access
in American Journal of Veterinary Research

Summary

The range of neutralizing activity to bovine viral diarrhea (bvd) virus and viral protein specificity of antibodies induced by 3 inactivated vaccines were evaluated by use of samples of sera obtained from 13 cattle 14 days after vaccination. Viral neutralizing antibodies were detected in all cattle to each of 10 noncytopathic and 10 cytopathic isolates of bvd virus. A viral-induced polypeptide (53,000 to 56,000 daltons) was detected by radioimmunoprecipitation with serum from all vaccinates. Other viral-induced polypeptides of 115,000, 80,000, 48,000, and 25,000 daltons were precipitated with sera from some vaccinates. Precipitation of those polypeptides was related to the vaccine used. When multiple viral polypeptides were precipitated, the 53,000- to 56,000-dalton polypeptide appeared immunodominant.

Free access
in American Journal of Veterinary Research

Abstract

Objective—To examine effects of co-infection with porcine reproductive and respiratory syndrome virus (PRRSV) and Bordetella bronchiseptica in pigs.

Animals—Forty 3-week-old pigs.

Procedure—30 pigs (10 pigs/group) were inoculated with PRRSV, B bronchiseptica, or both. Ten noninoculated pigs were control animals.

Results—Clinical signs, febrile response, and decreased weight gain were most severe in the group inoculated with both organisms. The PRRSV was isolated from all pigs in both groups inoculated with virus. All pigs in both groups that received PRRSV had gross and microscopic lesions consistent with interstitial pneumonia. Bordetella bronchiseptica was cultured from all pigs in both groups inoculated with that bacterium. Colonization of anatomic sites by B bronchiseptica was comparable between both groups. Pigs in the group that received only B bronchiseptica lacked gross or microscopic lung lesions, and B bronchiseptica was not isolated from lung tissue. In the group inoculated with B bronchiseptica and PRRSV, 3 of 5 pigs 10 days after inoculation and 5 of 5 pigs 21 days after inoculation had gross and microscopic lesions consistent with bacterial bronchopneumonia, and B bronchiseptica was isolated from the lungs of 7 of those 10 pigs.

Conclusions and Clinical Relevance—Clinical disease was exacerbated in co-infected pigs, including an increased febrile response, decreased weight gain, and B bronchiseptica-induced pneumonia. Bordetella bronchiseptica and PRRSV may circulate in a herd and cause subclinical infections. Therefore, co-infection with these organisms may cause clinical respiratory tract disease and leave pigs more susceptible to subsequent infection with opportunistic bacteria. (Am J Vet Res 2000;61:892–899)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine effects of intranasal inoculation with porcine reproductive and respiratory syndrome virus (PRRSV) or Bordetella bronchiseptica on challenge with nontoxigenic Pasteurella multocida in pigs.

Animals—Seventy 3-week-old pigs.

Procedure—In experiment 1, pigs were not inoculated (n= 10) or were inoculated with PRRSV (10), P multocida (10), or PRRSV followed by challenge with P multocida (10). In experiment 2, pigs were not inoculated (n = 10) or were inoculated with B bronchiseptica (10) or PRRSV and B bronchiseptica (10); all pigs were challenged with P multocida. Five pigs from each group were necropsied 14 and 21 days after initial inoculations.

ResultsPasteurella multocida was not isolated from tissue specimens of pigs challenged with P multocida alone or after inoculation with PRRSV. However, in pigs challenged after inoculation with B bronchiseptica, P multocida was isolated from specimens of the nasal cavity and tonsil of the soft palate. Number of bacteria isolated increased in pigs challenged after coinoculation with PRRSV and B bronchiseptica, and all 3 agents were isolated from pneumonic lesions in these pigs.

Conclusion and Clinical Relevance—Infection of pigs with B bronchiseptica but not PRRSV prior to challenge with P multocida resulted in colonization of the upper respiratory tract and tonsil of the soft palate with P multocida. Coinfection with PRRSV and B bronchiseptica predisposed pigs to infection of the upper respiratory tract and lung with P multocida. Porcine reproductive and respiratory syndrome virus and B bronchiseptica may interact to adversely affect respiratory tract defense mechanisms, leaving pigs especially vulnerable to infection with secondary agents such as P multocida. (Am J Vet Res 2001; 62:521–525)

Full access
in American Journal of Veterinary Research

Abstract

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.

Full access
in American Journal of Veterinary Research

Summary

Samples of sera were obtained from 5,725 cows in a semiclosed herd. In each of the preceding 7 years, the herd was vaccinated against bovine viral diarrhea (bvd) with killed virus. Neutralizing antibody tests were done on all samples of sera, using cytopathic virus, bvd-tgac virus, that was antigenically distinct from the vaccine virus. Most samples of sera had high titers of neutralizing antibodies against bvd-tgac virus. In 48 samples of sera, neutralizing antibodies were not detected against bvd tgac virus, but were detected against the vaccine virus. Neutralizing antibodies against selected noncytopathic bvd viruses were not detected in several samples of serum that had neutralizing antibodies against the vaccine virus and bvd-tgac virus. Noncytopathic bvd virus was isolated from sera obtained from 3 cows < 4 years old. Two cows were available for further testing, and persistent infection with bvd virus was confirmed in both cows. The bvd viruses isolated from those cows were not neutralized by several samples of sera. Immunoprecipitation of polypeptides induced by the vaccine virus was done with selected samples of serum. Two patterns of immunoprecipitated viral-induced polypeptides were identified. One pattern was consistent with exposure of cows with live virus. The other pattern was consistent with exposure of cows with only the killed virus vaccine.

Free access
in American Journal of Veterinary Research

Abstract

Objective—To determine whether cattle testing positive for Mycobacterium avium subsp paratuberculosisas determined by microbial culture of feces or antibody ELISA were more likely to have false-positive responses on the caudal fold tuberculin (CFT) test or interferon-γ (IFN-γ) assay for Mycobacterium bovis than cattle testing negative for M paratuberculosis.

Animals—1,043 cattle from 10 herds in Michigan.

Procedure—Feces and blood samples for plasma were collected from cattle ≥ 24 months old on the day the CFT test was read. Fecal samples were submitted for microbial culture for M paratuberculosis. Plasma samples were tested for antibody against M paratuberculosis, and IFN-γ after stimulation with purified protein derivative tuberculin from M bovis or M avium.

Results—Of 1,043 cattle, 180 (17.3%) had positive CFT test results (suspects) and 8 (0.8%) had positive IFN-γ assay results after stimulation with purified protein derivative tuberculin from M bovis. Forty-five (4.3%) and 115 (11.0%) cattle tested positive for M paratuberculosis as determined by microbial culture of feces and antibody ELISA, respectively. Cattle with positive responses for M paratuberculosis appeared to have an increased likelihood of false-positive results on the CFT test, although this association was not significant.

Conclusions and Clinical Relevance—No significant association was detected among cattle testing positive for M paratuberculosis as determined by microbial culture of feces and antibody ELISA and positive CFT test and IFN-γ assay results for M bovis. (J Am Vet Med Assoc 2005;226:429–435)

Full access
in Journal of the American Veterinary Medical Association