Minnesota had record numbers of several tick-borne diseases last year. The three most common infections sickened more than 2,000 people.
One disease, human anaplasmosis, affected twice as many people in 2010 than in previous years.
Three of Minnesota's most common tick-borne diseases are spread by the black-legged tick, also known as the deer tick. In addition to human anaplasmosis, the black-legged tick can also transmit babesiosis and Lyme disease.
Lyme disease gets the most attention because it typically accounts for the most illnesses. And last year's infection tally was no exception. There were 1,293 cases of Lyme disease -- a 21 percent increase from the previous year and a new record.
But health officials are more troubled by the sharp increase in human anaplasmosis cases. That infection can cause more serious illness, and even death.
Recent historical data show that roughly 300 Minnesotans contract human anaplasmosis each year. But in 2010, that number suddenly surged to 720 cases. About a third of the victims were hospitalized and one elderly patient died.
Health Department epidemiologist Dave Neitzel attributes the dramatic increase in cases, in part, to more awareness and better testing. But he says there's no doubt that an explosion in the tick population has also been a factor.
"We've been finding ticks in a lot of places where we had not found them previously," he said.
2010 was an ideal year for black-legged ticks. It was warm and moist -- two crucial ingredients to the ticks' survival. Not only did they thrive in those conditions, they also expanded their range.
Neitzel says last year was the first time that tick-borne diseases were reported in people who live north of Grand Rapids and Bemidji. There were also some disease cases in western Minnesota.
Six Minnesota counties had more human anaplasmosis cases than Lyme disease cases last year. They were Aitkin, Beltrami, Carlton, Cass, Crow Wing and Hubbard counties.
Retired University of Minnesota professor and tick expert Russ Johnson is not surprised by the data. He says it mirrors circumstances he found among small animals he studied in the Camp Ripley area, also in central Minnesota.
Johnson, who will publish a paper on his findings soon, says white-footed mice and chipmunks in the Camp Ripley area had very high levels of anaplasmosis. So it makes sense to him that people in those areas who were bitten by ticks would have higher rates of the infection too.
Johnson says these findings are especially important for doctors, because the treatment for the dieases is different.
"You normally treat Lyme disease with penicillin. Penicillin is not effective against anaplasmosis, whereas antibiotics such as tetracycline will act on both," said Johnson. "So in these areas where you have a lot of anaplasmosis, the use of tetracycline is important."
Black-legged ticks are most active between mid-May and mid-July.
The Health Department says the best way to prevent bites is by using an insect repellant that contains DEET, and by avoiding the wooded and brushy areas where the ticks live.
Homeowners can also reduce the number of ticks in their yards by clipping their grass short, raking up leaves and putting down a dry landscape barrier of wood chips or stone between their lawn and the woods.