ST. PAUL — Minnesota residents may believe this past winter was rough, but state health officials said it wasn’t bad enough to kill off the deer ticks that carry Lyme disease.

Dave Neitzel, an epidemiologist with the Minnesota Department of Health, told Minneapolis Public Radio that the cold kills ticks only if the insects are exposed to the air, and that the insects mostly survived the harsh cold this winter by staying insulated under a thick blanket of snow.

The health department has been conducting field surveys in areas that are historically tick infested. Early results indicate there are more deer ticks now compared to this time last year.

“We have a little piece of cloth that we drag behind us in the woods and we stop every 15 to 20 meters and we pull ticks off of ourselves and pull ticks off of the cloth,” Neitzel said. “A very simple sampling method, but it works really well.”

Deer ticks carry Lyme disease, which can cause fever and fatigue, joint damage and, if left untreated, heart and neurological problems. Since he began studying tick-borne diseases in the 1980s, Neitzel said Minnesota has gone from experiencing a handful of Lyme cases every year to more than a thousand.

He urged outdoor enthusiasts who spend time in brushy or wooded areas to protect themselves from tick bites with repellents containing DEET or — his preference — permethrin, especially during May, June and July, when Lyme disease is most prevalent.

“It can be applied to clothing before you go out,” said Neitzel. “It not only kills ticks effectively, but it’s a strong repellent too.”