WINNIPEG, Manitoba (Reuters) - Five more cases of bovine tuberculosis have been confirmed in cattle from the same Alberta herd as a cow slaughtered in the United States in September that was found to have the disease, Canada's food system regulator said on Friday.

"These positive test results indicate transmission between animals has occurred," said Penny Greenwood, national manager of domestic disease control for Canadian Food Inspection Agency (CFIA). She told reporters that there was now greater risk that the disease had spread to more herds.

The government has placed 34 farms in southeast Alberta and two farms in southwest Saskatchewan under quarantine, keeping thousands of head of cattle from being moved as it tests them for the disease.

Cattle from the infected herd are being destroyed.

Canada is the sixth largest exporter of beef and veal, according to the U.S. Department of Agriculture.

Bovine tuberculosis is a contagious disease caused by bacteria that are closely related to the bacteria that causes tuberculosis in humans and birds, resulting in illness, coughing and death, according to the World Organization for Animal Health (OIE).

Humans can become infected by drinking raw milk from infected cows.

Food safety is not at risk since cattle are examined for disease at slaughter plants and the meat of any animal that appears sick is not sold for human consumption, Greenwood said. She said there were no implications for international trade.

The tuberculosis strain is related to one previously detected in cattle in Mexico and not seen before in Canada, Greenwood said. The strain could have entered Canada through humans, imported cattle from the United States, or wildlife crossing the border.

(Reporting by Rod Nickel in Winnipeg, Manitoba; Editing by Toni Reinhold)