The decaying carcasses, spread over an area of 10 square kilometres northwest of Fort Providence, were spotted on a routine surveillance flight on July 3.
The dead animals field-tested positive for anthrax, a naturally occurring spore exacerbated by hot periods following extreme wetness.
As a precaution, the Department of Environment and Natural Resources (ENR) has issued an alert to deal with the potential outbreak.
The area the animals were found is home to a number of winter trappers’ cabins. Accessible only by boat, it has been closed to picnickers since the animals were discovered.
Anyone who discovers a carcass is asked to notify ENR as soon as possible. People are advised not to approach or touch carcasses.“(The bison) are usually wallowing because they want to cool off. The spores get released from the ground and they inhale them,” said Judy McLinton of the department of environment and natural resources.
The quick-moving anthrax spores cause the affected animals to have stiff-legged gait that quickly immobilizes them with splayed “saw-horse” legs. They appear indifferent to people, and may have a frothy discharge from the nostrils. Death comes within 72 hours.
It will take up to six weeks to dispose of the rotting hulks, officials said. A team will first treat the animals with formaldehyde to deter scavengers and kill spores before they burn the remains.
The dead animals were part of the Mills Lake, area herd of about 300 animals. The animals belong to the Mackenzie Bison Sanctuary herd of 2,000 prairie-loving bison. Unusual in the bison world, the herd is considered disease-free, without the tuberculosis and brucellosis that plague their bison brothers in the Slave River and Wood Buffalo herds, McLinton said.
In 1993, 172 bison from the Slave River herd were killed by anthrax. In 2010, an outbreak killed nine animals.
Samples have been sent to the Canadian Food Inspection Agency lab in Lethbridge.