There is evidence to suggest that plague is circulating in the southwestern Prairies, British Columbia, North Dakota and Montana.

A study in 1995 tested 240 dogs and 242 cats in rural areas surrounding four provincial parks for antibodies against the bacteria, which is an indicator of exposure.

Researchers found that 10 percent of dogs and five percent of cats had evidence of exposure to plague. Dogs that eat the bacteria are unlikely to develop clinical plague. However, they do produce antibodies against the bacteria within a few weeks.

Cats, on the other hand, are far more likely to die of plague. This explains why a greater proportion of dogs have antibodies; many exposed cats probably died.

In 1988, two bushy-tailed woodrats were found dead in British Columbia and tested positive for the bacteria. A small survey of wild carnivores in the province discovered that three percent had evidence of exposure to the bacteria.

The bacteria that causes the bubonic plague, Yersina pestis, was named for its discoverer, Alexandre Yersin. He worked as a bacteriologist in Hong Kong in the late 1800s, where he associated the bacteria with people dying from bubonic plague.

He had the intuition to test rodents and discovered they also carried the bacteria, leading him to suggest that rodents were a potential source of infection for people.

Fleas from infected rodents transmit the bacteria. They leave the body of infected rodents when they die and seek out the nearest warm mammal, which could be a human.

The bacteria occasionally infect a victim’s lung and become aerosolized. Coughing can spread it between people in a more rapid mode of transmission, resulting in pneumonic plague.

In Canada, ground squirrels (gophers) and other rodents are suspected to maintain the bacteria, although exactly how plague is maintained in these areas remains unknown.

Plague is responsible for wiping out large segments of the prairie dog population and indirectly, the black footed ferret, which preys upon them.

Only a small pocket of prairie dogs remains in Canada, in and around Grasslands National Park.

People are more likely to be ex-posed and infected in years with heavy plague outbreaks in carrier rodents.

Infected animals and their fleas can be sources of infection to people. Cats with the plague can infect people through bites, scratches or their respiratory secretions. Cats are also good at delivering infected rodents to places where people may contact them.

People can protect themselves by recognizing that they live in a plague zone, avoid contact with dead rodents and sick outdoor cats and wear protective gear when this is unavoidable.

Plague in prairie residents is uncommon. A man from southeastern Alberta died of the plague in 1939.

Sixty percent of infected people will die if the disease is left untreated. Approximately 3,000 human cases of bubonic plague are reported worldwide each year. Bubonic plague has been identified as a potential bioterrorism agent.

Modern science has pinned down the origin of this bacteria to China or surrounding areas. Human trade brought the bacteria west in the 14th century and worldwide in the 19th century.

The famous Black Death in the 14th century killed an estimated 25 million people in four years, which was one-third of the people in Europe at the time. The rapid spread of the disease is especially frightening.

The later 19th century pandemic occurred when rodent stowaways boarded ships. Plague spread across western North America from the ports of San Francisco and never went away.

Jamie Rothenburger is a veterinarian practising at Crossfield, Alta.

Jamie Rothenburger is a veterinarian practising at Crossfield, Alta.