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
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
Objective—To evaluate economic effects and health and performance of the general cattle population after exposure to cattle persistently infected (PI) with bovine viral diarrhea virus (BVDV) in a feedlot.
Animals—21,743 high-risk calves from the southeastern United States.
Procedures—PI status was determined by use of an antigen-capture ELISA (ACE) and confirmed by use of a second ACE, reverse transcriptase–PCR assay of sera, immunohistochemical analysis, and virus isolation from sera. Groups with various amounts of exposure to BVDV PI cattle were used. After being placed in the feedlot, identified PI cattle were removed from 1 section, but PI cattle remained in another section of the feedlot. Exposure groups for cattle lots arriving without PI animals were determined by spatial association to cattle lots, with PI animals remaining or removed from the lot.
Results—15,348 cattle maintained their exposure group. Performance outcomes improved slightly among the 5 exposure groups as the risk for exposure to BVDV PI cattle decreased. Health outcomes had an association with exposure risk that depended on the exposure group. Comparing cattle lots with direct exposure with those without direct exposure revealed significant improvements in all performance outcomes and in first relapse percentage and mortality percentage in the health outcomes. Economic analysis revealed that fatalities accounted for losses of $5.26/animal and performance losses were $88.26/animal.
Conclusions and Clinical Relevance—This study provided evidence that exposure of the general population of feedlot cattle to BVDV PI animals resulted in substantial costs attributable to negative effects on performance and increased fatalities.
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.
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.
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 determine efficacy of a modified-live virus (MLV) vaccine containing bovine viral diarrhea virus (BVDV) 1a and 2a against fetal infection in heifers exposed to cattle persistently infected (PI) with BVDV subtype 1 b.
Animals—50 heifers and their fetuses.
Procedures—Susceptible heifers received a placebo vaccine administered IM or a vaccine containing MLV strains of BVDV1a and BVDV2a administered IM or SC. On day 124 (64 to 89 days of gestation), 50 pregnant heifers (20 vaccinated SC, 20 vaccinated IM, and 10 control heifers) were challenge exposed to 8 PI cattle. On days 207 to 209, fetuses were recovered from heifers and used for testing.
Results—2 control heifers aborted following challenge exposure; both fetuses were unavailable for testing. Eleven fetuses (8 control heifers and 1 IM and 2 SC vaccinates) were positive for BVDV via virus isolation (VI) and for BVDV antigen via immunohistochemical analysis in multiple tissues. Two additional fetuses from IM vaccinates were considered exposed to BVDV (one was seropositive for BVDV and the second was positive via VI in fetal tissues). A third fetus in the SC vaccinates was positive for BVDV via VI from serum alone. Vaccination against BVDV provided fetal protection in IM vaccinated (17/20) and SC vaccinated (17/20) heifers, but all control heifers (10/10) were considered infected.
Conclusions and Clinical Relevance—1 dose of a BVDV1a and 2a MLV vaccine administered SC or IM prior to breeding helped protect against fetal infection in pregnant heifers exposed to cattle PI with BVDV1b.
Objective—To evaluate diagnostic tests used for detection of bovine viral diarrhea virus (BVDV) and determine the prevalence of BVDV subtypes 1a, 1b, and 2a in persistently infected (PI) cattle entering a feedlot.
Procedures—Samples were obtained from calves initially testing positive via antigen capture ELISA (ACE) performed on fresh skin (ear notch) specimens, and ACE was repeated. Additionally, immunohistochemistry (IHC) was performed on skin specimens fixed in neutral-buffered 10% formalin, and reverse transcriptase PCR (RT-PCR) assay and virus isolation were performed on serum samples. Virus was subtyped via sequencing of the 5′ untranslated region of the viral genome.
Results—Initial ACE results were positive for BVDV in 88 calves. After subsequent testing, results of ACE, IHC, RT-PCR assay, and viral isolation were positive in 86 of 88 calves; results of all subsequent tests were negative in 2 calves. Those 2 calves had false-positive test results. On the basis of IHC results, 86 of 21,743 calves were PI with BVDV, resulting in a prevalence of 0.4%. Distribution of BVDV subtypes was BVDV1b (77.9%), BVDV1a (11.6%), and BVDV2a (10.5%).
Conclusions and Clinical Relevance—Rapid tests such as ACE permit identification and segregation of PI cattle pending results of further tests, thus reducing their contact with the rest of the feedlot population. Although vaccines with BVDV1a and 2a components are given to cattle entering feedlots, these vaccines may not provide adequate protection against BVDV1b.