Submitted to: Journal of Veterinary Diagnostic Investigation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/30/2001
Publication Date: N/A
Interpretive Summary: A retrospective and prospective study was undertaken to establish the importance of malignant catarrhal fever (MCF) in bison at feedlot. The study revealed that losses due to MCF were very significant at the feedlot, which exceeded the losses due to other diseases. The study underscored distinctive features of MCF in bison. Most typical lesions for MCF in bison were milder and more localized than seen in cattle with MCF. No single tissue could be relied upon to establish a morphological diagnosis of MCF in bison, explaining why some early cases were misdiagnosed. PCR for sheep-associated MCF viral DNA is reliable test for clinical confirmation of MCF in bison. In the prospective part of this study, the fate of a group of 300 healthy male bison in the feedlot was followed for up to 7 months. At entry, 23% (71/300) of bison were seropositive for MCF viruses, and 11% (8/71) of these seropositive bison were PCR-positive for OvHV-2. There was no apparent change in seroprevalence in the group during the investigation. Twenty two (7.3%) of the 300 bison died in the feedlot. Of these, 15 had MCF, 4 had acute or chronic pneumonia, and 3 were unexamined. The study also indicated longer duration studies of bison in herds are necessary to establish whether subclinically infected animals are more likely than seronegative animals to develop clinical MCF.
Technical Abstract: A fatal enteric syndrome was identified in American bison at a large feedlot in the American Midwest in early 1998. An estimated 150 bison died of the syndrome between January 1998 and December 1999. The syndrome was due to malignant catarrhal fever, primarily the alimentary form. Clinical onset was acute with affected bison dying within 1-3 days. Recovery did not toccur. Consistent lesions were hemorrhagic cystitis, ulcerative enterotyphlocolitis, and arteritisphlebitis. Vasculitis was milder and more localized than seen in cattle with MCF and, unlike cattle, lymphadenomegaly was minimal. Virtually all affected bison examined were positive for ovine herpesvirus-2(OvHV-2). A retrospective study of archived tissues established that MCF occured in the yard as early as 1993. A prospective study was undertaken to establish the importance of MCF relative to other fatal diseases at the feedlot. The fate of a group of 300 0healthy male bison in a consignment of 1101 was followed for up to 7 month to slaughter. At entry, 23%(71/300) of bison were seropositive for MCF viruses, and 11%(8/71) of these seropositive bison were PCR-positive for OvHV-2. All 40 randomly selected, seronegative bison were PCR-negative. There was no apparent change in seroprevalence in the group during the investigation. Twenty two (7.3%) of the 300 bison died in the feedlot. Of these, 15 had MCF, 4 had acute or chronic pneumonia, and 3 were unexamined. Losses in the entire consignment were higher (98/1101; 8.8% death loss) with 76% of deaths attributable to MCF. The study failed to reveal a relationship between subclinical infection and development of clinical disease.