Vitro and In Vivo Bovine Viral Susceptibility
Chiharu Shiratori and Christopher C.L. Chase
From Masters of Science Thesis, Veterinary
The study of bovine viruses in American bison (Bison bison) is necessary because bison are in close contact with cattle. The susceptibility of bison cells to seven bovine viruses: bovine herpesvirus 1 (BHV-1), bovine respiratory syncytial virus (BRSV), cytopathic (CP) and noncytopathic (NCP) bovine viral diarrhea virus (BVDV) type I and type II, and bluetongue virus (BTV) was examined. Bison cells were susceptible to bovine viruses, but the virus grew slower in bison cells than in bovine cells. In both cell types, BHV-1 growth in bison cells was 101.5 times greater at 24 hours and 10 0.5 times greater at 48 hours than in bovine cells. With the exception of BHV-1; BRSV, BTV, and CP and NCP BVDV type I and type II grew faster and at higher levels in bovine cells than in bison cells although NCP BVDV type I and type II showed similar virus growth curves. In BRSV growth, the bison cells produced 100.5 – 103 times less virus, and the lag in peak virus production in bison cells was 24 hours later than in bovine cells. In CP BVDV type I and type II growth, the peak titers were 100.5 – 103.5 times lower in bison cells, and the lag in peak virus production in bison cells was 12-48 hours later than bovine cells. In BTV growth, the difference ranged from 10 0.5 – 106 times less virus in bison cells, and the lag in peak virus production was 24 hours later than bovine cells. The conclusion is that bison cells are susceptible to BHV-1, BRSV, CP and NCP BVDV type I and II, and BTV infection and virus replication. For most viruses, the level of virus production is lower in bison kidney cells, than in bovine kidney cells.
erology tests were done to determine the prevalence of BHV-1, CP BVDV type I and type II, and BRSV in two bison herds in western South Dakota. In the BRSV SN test, the result showed that bison had a high exposure to BRSV in both bison herds. In herd A, older bison (2-years old) had a 99 percent BRSV seroprevalence (Geometric mean titer [GMT] = 3.8), and younger bison (< 7 months old) had an 87 percent BRSV seroprevalence [GMT] = 3.07). In herd B, older bison (> 2 years old) had a 90 percent BRSV seroprevalence (GMT = 3.69), while younger bison (< 1 year old) had a 14 percent BRSV seroprevalence (GMT = 1.13). The BRSV seroprevalence was high in both herds, although older bison in herd A received a killed BRSV vaccine. This high seroprevalence is probably due to BRSV circulation in both bison herds, especially in herd A because younger unvaccinated bison also showed a high BRSV seroprevalence. There were no reports of BRSV clinical signs in either herd. BHV-1 and BVDV titers in older bison in herd A and BHV-1 titers in older bison in herd B were reflected to the use of vaccines and there are probably no BVDV or BHV-1 circulation in the herds. In herd A, the percentage of younger bison that had antibodies against BHV-1 (15%, GMT = 1.19) was higher than older bison (5%, GMT-8.17). The higher percentage of BHV-1 titer levels in the bison calves was an unexpected result because we had expected older animals that had been vaccinated would have higher titers to these viruses than younger animals. The higher titers in the calves from herd A may be the result of maternal antibodies in the bison calves younger than 4 or 5 months old because a BHV-1 killed vaccine was used for cows.
A rabbit polyclonal anti-bison immunoglobulin G was developed, and the sensitivity of anti-bison and anti-bovine reagents was compared. Results showed that the commercial BHV-1 antibody enzyme-linked immunosorbant assay (IBR-ELISA) bovine kit (IDEXX< Westbrook, ME) was not suitable for a comparison between bison reagents and bovine reagents. The indirect immunofluorescence assay (IFA) results indicated that both bovine and bison reagents can be used for diagnosis of bison infectious diseases. In the IFA test, we used the anti-bison IgG:FITC conjugate and a commercial anti-bovine IgG:FITC conjugate. We used different working dilutions of each reagent due to differences in IgG concentration and purity. The results showed that the anti-bison reagent (dilution 1:30) and a commercial bovine reagent (dilution 1:50) detected 100 percent of BHV-1 positive bovine and bison sera. When conducting the IFA, the bison reagent (dilution 1:40) and the bovine reagent (dilution 1:75) were used. The bison or bovine reagents did not detect BHV-1 antibodies in bison sera at a 1:4 SN titer, while they detected BHV-1 antibodies at a 1:4 SN titer in bovine sera. These results demonstrated that the ELISA kit failed to work with the bison reagent. The commercial ELISA kit used special reagents that were not suited for bison reagents. Bison and bovine reagents can detect BHV-1 antibodies using the IFA.
Mineral levels in bison tissues and bison sera between feedlot bison and free ranging bison were determined using the inductivity coupled plasma-optical emission spectrometers (ICP-OES) in the Olson Biochemistry Laboratory at South Dakota State University. In bison kidney samples (Table 1), concentrations of copper, iron, manganese, and zinc were significantly higher (P<0.05) in feedlot bison, and the concentration of selenium was significantly higher (P<0.001) in feedlot bison than in free-ranging bison. In bison liver samples (Table 2), concentrations of copper and zinc were significantly higher (P<0.05) in feedlot bison than in free-ranging bison, and the concentration of iron was significantly higher (P<0.05) in free ranging bison than in feedlot bison. In bison sera (Table 3), the concentration of copper was significantly higher (P<0.05), and the concentration of zinc was significantly higher (P<0.001) in feedlot bison than free-ranging bison. The value of iron was significantly higher (P<0.05), and the concentration of molybdenum was significantly higher (P<0.001) in free-ranging bison than in feedlot bison. These differences may be attributed to nutritional effects. The molybdenum levels in free ranging bison showed higher levels than in feedlot bison (P<0.001). The normal molybdenum levels in bison sera are currently not available; therefore we cannot say whether the molybdenum level of these free ranging bison is abnormal. However, since excess molybdenum can interfere with copper metabolism, the understanding of the molybdenum level will be further studied. In this study, we compared mineral levels between feedlot bison and free ranging bison. In all samples, there are significant differences in the levels of copper, iron, and zinc, and there are no significant differences in the levels of calcium and magnesium.
From this study, we learned that bison are susceptible to bovine viruses in vivo and in vitro; some mineral levels were significantly different between feedlot bison and free ranging bison; and both bovine and bison reagents can be used for diagnosis of viral infectious diseases in American bison. Further studies should be pursued to understand viral infectious diseases in both bison raised by wildlife agencies and groups, and by commercial bison meat producers because our understanding of these bison diseases is still in the early stages.
Table 1a: Mineral levels in feedlot bison kidney (parts per million=ug/g, as is basis)
Table 1b: Mineral levels of free-ranging bison kidney (parts per million=ug/g, as is basis)
Cu: Copper, Fe: Iron, Mn: Manganese, Mo: Molybdenum, Se: Selenium, Ca: Calcium, Mg: Magnesium, Zn: Zinc
(P<0.05) different from feedlot bison
Table 2a: Mineral levels in feedlot bison liver (parts per million=ug/g, as is basis)
Table 2b: Mineral levels of free-ranging bison liver (parts per million=ug/g, as is basis)
Unit = ppm (ug/g)
Table 3a: Mineral levels in feedlot bison, Sera<0.008 (parts per million=mg/L)
Table 3b: Mineral levels of free-ranging bison, Sera<0.008 (parts per million=mg/L)
Cu: Copper, Fe:
Iron, Mn: Manganese, Mo: Molybdenum, Se: Selenium, Ca: Calcium, Mg:
Magnesium, Zn: Zinc
 Normal mineral levels in bison liver