Salt Lake City ? Cases of a deadly strain of a horse virus have more than doubled in the past week and suspected cases have forced the quarantine of 15 more facilities.

The U.S. Department of Agriculture says Friday there are 75 confirmed cases in 9 states and 61 facilities have suspected or confirmed cases.

The agency says 11 horses have been euthanized and 17 more have shown signs of the neurological problems that often lead to death.

Last week, there were 34 confirmed cases and 9 horses had died.

Horses from Alberta and British Columbia were also infected. Canadian officials are not reporting new cases.

The outbreak of the equine herpes virus started at an Ogden, Utah, horse show earlier this month and has forced the cancellation of multiple events.