Spotting a rat in Alberta is a rare and frightening occurrence. Since the 1950s, the province has boasted about its rat-free status, crediting an aggressive extermination program.

But the province’s famous “rat patrol” is stumped after rats were found in Calgary and Medicine Hat.

About 60 rats have been killed in a Medicine Hat landfill since a colony was discovered there last week. Six rodents were spotted in the city and another 16 emerged in the surrounding Cypress County.

Single Norway rat sightings have been reported in the area since spring.

On Friday, Calgary city officials said a resident found a dead rat near his property. The Animal and Bylaw Services Department suspects the rat was an escaped pet, but that has not been confirmed.

As a result, the southeast neighbourhood will be closely monitored for any other rat activity.

"We take this as a high priority for us, so if people have any thoughts that they've seen a rat, call us right away," said Greg Steinraths, acting director of animal services.

No one knows for sure where the rats came from.

Agricultural fieldmen known as the “rat patrol” eliminate rats within a designated control zone 600 kilometres long and 30 kilometres wide along the province's eastern boundary.

Alberta says such measures have prevented an estimated $1 billion in damage that would have been caused by rats over the last five decades.

Now, Medicine Hat's waste manager Ed Jollymore said officials will use all available resources to defend Alberta’s rat-free status.

Bull snakes will be taken to the landfill where the rat colony was found so they can eat any remaining rodents. Traps and cameras have also been set up to track the vermin.

“They do carry disease. That’s another main reason they are on the pest list,” said Jason Storch, an agricultural fieldman in Cypress County. “They are a real nuisance.”

Animal control officials say one pair of rats can begin a chain of breeding that spawns up to 15,000 offspring a year.

With a report from CTV Edmonton, CTV Calgary and files from The Canadian Press