Malignant catarrhal fever in bison, acute and chronic cases

Area of Science:

• Veterinary Pathology
• Virology
• Wildlife Disease

Background:

• Malignant catarrhal fever (MCF) is a severe, often fatal, lymphoproliferative disease affecting various ruminants.
• Ovine herpesvirus 2 (OvHV-2) is the primary causative agent of MCF in many regions.
• Bison are known to be susceptible to MCF, but clinical presentations can vary.

Purpose of the Study:

• To describe the clinical and pathological findings in bison diagnosed with acute and chronic malignant catarrhal fever.
• To identify characteristic lesions associated with MCF in bison.
• To confirm the presence of ovine herpesvirus 2 in affected bison tissues using molecular methods.

Main Methods:

• Necropsy and histopathological examination of tissues from bison diagnosed with MCF.
• Detailed recording of clinical signs and gross lesions.
• Polymerase chain reaction (PCR) for the detection of ovine herpesvirus 2 DNA in formalin-fixed tissues.

Main Results:

• Acute MCF in 10 bison presented with diverse signs including ocular, respiratory, and gastrointestinal issues, and characteristic vasculitis with lymphoid infiltrates.
• Alimentary tract and urinary bladder ulcerations/hemorrhages were common in acute cases.
• Chronic MCF in one bison showed progressive neurological signs and distinct chronic vascular lesions, with retinal infarction.
• Ovine herpesvirus 2 DNA was detected in tissues from all MCF-affected bison but not in unaffected controls.

Conclusions:

• Ovine herpesvirus 2 is confirmed as the causative agent of MCF in these bison cases.
• MCF in bison can manifest with varied clinical signs and pathological lesions, encompassing both acute and chronic forms.
• Vasculitis is a consistent finding in both acute and chronic MCF in bison, highlighting its central role in pathogenesis.