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- Author or Editor: John D. Neill x
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Objective—To correlate tissue distribution with development of lesions after experimental infection with a virulent strain of noncytopathic bovine viral diarrhea virus (BVDV) type 2 in calves.
Animals—Ten 14-day-old and two 2-month-old colostrum-deprived calves.
Procedure—Calves were intranasally inoculated with BVDV type-2 strain 1373 from an outbreak of clinically severe bovine viral diarrhea (BVD). Two 14-day-old calves served as noninfected controls. Two calves each were euthanatized on postinoculation days 3, 6, and 12, and 1 each on days 8, 9, 13, and 14. Tissues were collected for immunohistologic and histologic examination.
Results—Inoculated calves developed nonspecific clinical signs characterized by high fever and decreased numbers of leukocytes and thrombocytes. Viral antigen was detected focally in lymphoid tissues on day 3. On days 6, 8, 9, 12, and 14, viral antigen became increasingly widespread throughout organs and tissues. Viral antigen in lymphoid tissues was associated with severe depletion of all compartments. Lesions in other tissues were not well correlated with distribution of viral antigen. Depletion of lymphoid tissues was observed in a calf on day 13, but viral antigen had been cleared from most tissues and was detected in vascular walls only.
Conclusions and Clinical Relevance—Infection with a virulent BVDV strain resulted in wide dissemination of viral antigen in host tissues. Severe lymphoid depletion developed in lymphoid tissues, whereas viral antigen was generally not associated with lesions in other tissues. Findings suggest that development of lesions in acute BVD is not solely a function of viral replication and is also attributable to host reaction to infection. (Am J Vet Res 2002;63:1575–1584
Objective—To determine whether passively acquired antibodies prevent development of a protective immune response to live virus in calves.
Procedure—Calves were caught immediately after birth and tested free of bovine viral diarrhea virus (BVDV) and serum antibodies against BVDV. Within 48 hours, 12 calves were fed colostrum that contained antibodies against BVDV and 6 calves received BVDV antibody free milk replacer. Three milk replacer fed and 6 colostrum fed calves were exposed to virulent BVDV2-1373 at 2 to 5 weeks of life when passively acquired serum antibody titers were high. After serum antibody titers against BVDV had decayed to undetectable concentrations (at 7 to 9 months of age), the 3 remaining milk replacer fed calves, 6 colostrum fed calves previously exposed to BVDV2-1373, and 6 colostrum fed calves that had not been exposed to the virus were inoculated with BVDV2-1373.
Results—Passively acquired antibodies prevented clinical disease in inoculated colostrum fed calves at 2 to 5 weeks of life. Serum antibody titers did not increase in these calves following virus inoculation, and serum antibody titers decayed at the same rate as in noninoculated colostrum fed calves. Inoculated colostrum fed calves were still protected from clinical disease after serum antibody titers had decayed to nondetectable concentrations. Same age colostrum fed calves that had not been previously exposed to the virus were not protected.
Conclusion and Clinical Relevance—A protective immune response was mounted in calves with passive immunity, but was not reflected by serum antibodies titers. This finding has implications for evaluating vaccine efficacy and immune status. (Am J Vet Res 2003;64:65–69)
Objective—To inoculate white-tailed deer (Odocoileus virginianus) during the sixth or seventh week of gestation with bovine viral diarrhea virus (BVDV) and observe for signs of reproductive tract disease during a 182-day period.
Animals—10 pregnant white-tailed deer (8 seronegative and 2 seropositive [control deer] for BVDV).
Procedures—Deer were inoculated with 1 of 2 deer-derived BVDV strains (RO3-20663 or RO3-24272). Serum anti-BVDV antibody titers were determined prior to and 21 or 35 days after inoculation. Virus isolation (VI) procedures were performed on tissues from fetuses and does that died and on blood samples collected from live fawns. Ear notch specimens obtained from live fawns were assessed by use of BVDV antigen-capture ELISA (ACE).
Results—Both RO3-20663–inoculated seropositive deer gave birth to apparently normal fawns. Among the RO3-24272–inoculated seronegative deer, 1 died, and 1 aborted and 1 resorbed their fetuses; among the RO3-20663–inoculated seronegative deer, 3 died, 1 aborted its fetus, and 1 gave birth to 2 fawns that were likely persistently infected. On the basis of VI and ACE results, those 2 fawns were positive for BVDV; both had no detectable neutralizing anti-BVDV antibodies in serum.
Conclusions and Clinical Relevance—Reproductive tract disease that developed in pregnant white-tailed deer following BVDV inoculation was similar to that which develops in BVDV-exposed cattle. Methods developed for BVDV detection in cattle (VI, immunohistochemical evaluations, and ACE) can be applied in assessments of white-tailed deer. Fawns from does that had serum anti-BVDV antibodies prior to inoculation were protected against BVDV infection in utero.
Case Description—136 pregnant beef cows were purchased in the fall of 2003. The following spring, 128 cows calved as expected; 8 cows were believed to have aborted with the fetuses unavailable for evaluation. Of the 128 calves born, 8 died within 2 weeks after birth and 9 were born with congenital abnormalities.
Clinical Findings—Cows and their calves were evaluated for bovine viral diarrhea virus (BVDV) infection. Forty-four of 120 calves, but 0 cows, tested positive for BVDV antigen by immunohistochemical staining of ear notch specimens.
Treatment and Outcome—Five BVDV test–positive calves died shortly after weaning, and the remaining 39 BVDV test–positive calves were moved to an isolated feedlot and retested for BVDV at 5 to 6 months of age; 36 had positive results, which indicated that they were persistently infected (PI) with BVDV, whereas 3 had negative results, which indicated that they were transiently infected with BVDV at the time of the first test. All PI calves were infected with the same BVDV type 2a strain. As yearlings, 17 of the 36 PI calves died peracutely with lesions consistent with mucosal disease, 6 died without gross lesions, and 2 were euthanized because of chronic ill thrift. The remaining 11 PI calves appeared healthy and were sold for slaughter. Screening of the following year's calf crop for BVDV by use of immunohistochemical staining of ear-notch specimens yielded negative results for all calves.
Clinical Relevance—Introduction of BVDV into a naïve cow herd resulted in a loss of 44% of the calf crop subsequent to reproductive loss, poor thrift, and mucosal disease.
Objective—To compare acute infection of cattle exposed to a high-virulence (HV) bovine viral diarrhea virus (BVDV), low-virulence (LV) BVDV, or HoBi-like virus.
Animals—24 Holstein bull calves.
Procedures—Colostrum-deprived 2- to 4-week-old calves, free of BVDV antigen and antibodies, were allocated into 4 groups (6 calves/group). Calves in 3 groups were exposed to an LV BVDV strain (BVDV2-RS886), an HV BVDV strain (BVDV2–1373), or a HoBi-like virus (D32/00 HoBi), whereas calves in the fourth group were not exposed to a virus but were cohoused with calves exposed to the HoBi-like virus. Circulating WBCs, platelets, rectal temperature, and presence of virus in the blood were monitored.
Results—Infection of calves with any of the 3 viruses resulted in reduced numbers of circulating WBCs. Pyrexia was detected in all calves exposed to HV BVDV or LV BVDV but in only 3 of 6 calves exposed to the HoBi-like virus. Diarrhea was observed in 0 of 6 calves exposed to the HoBi-like virus, 2 of 6 calves exposed to the LV BVDV, and 6 of 6 calves exposed to the HV BVDV. The HoBi-like virus was transmitted from acutely infected calves to naïve cohorts.
Conclusions and Clinical Relevance—The HoBi-like viruses are an emerging species of pestivirus isolated from water buffalo and cattle in South America, Southeast Asia, and Europe but not from cattle in the United States. Understanding the clinical course of disease caused by HoBi-like pestiviruses will be important for the design of surveillance programs for the United States.
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.