None of the three bison found in the Yellowstone River died from malignant catarrhal fever. Lab results received today regarding the second and third bison tested echo the results of the first bison tested. In all three cases, the tissues show no sign of disease and the exact cause of death cannot be determined.
However, upon discovery, all three bison showed visible signs of trauma according to FWP Wildlife Veterinarian Jennifer Ramsey. She believes this trauma – including fractured pelvises on two bison and crushed ribs on a third – occurred before death. These injuries could have resulted from the animals being swept into rocks during high water or other blunt force trauma. Every year, animal carcasses wash downstream from Yellowstone National Park into Montana.
The dead bison were spotted in the Yellowstone River in mid May. FWP crews retrieved tissue samples from each bison: the first near Emigrant, and the other two closer to Gardiner.
Given the recent introduction of domestic sheep in the Gardiner area, FWP looked into the possibility of malignant catarrhal fever in these bison. Malignant catarrhal fever is a viral disease which may be carried by domestic sheep without any symptoms, but can cause fatal infections in bison.