MINNEAPOLIS (AP) -- Minnesota reached a record number of diseases spread by deer ticks last year, prompting state health officials to warn people to stay on guard this summer.
Doctors diagnosed 465 cases of Lyme disease in the state last year, up 64 percent from 1999. Cases of a potentially fatal but less-known tick condition called human granulocytic ehrlichiosis more than doubled to 79 last year.
Both diseases are transmitted by the deer tick.
"That's a pretty substantial increase," said Dave Neitzel, a specialist in tick-borne diseases at the Minnesota Health Department.
National figures for either condition were not available for 2000, but Russell Johnson, a tick-disease expert at the University of Minnesota, said it appears that Lyme disease cases are dropping nationally.
In Minnesota, the increase could be because the public is more aware of tick diseases and reporting more cases. Another possible factor is more Minnesotans are moving into wooded housing developments, which would explain Lyme increases in Anoka and Washington counties, Neitzel said.
Some experts also believe Minnesota may have more deer ticks, especially in the state's northern and north-central counties where many people spend vacations. Neitzel said last year's warm, humid conditions allowed ticks to reproduce in large numbers.
About 20 percent of ticks in Minnesota are infected with the Lyme bacteria, Neitzel said. In other areas of the country, particularly the Northeast, up to 50 percent of ticks are affected.
Ticks could be migrating into Minnesota by hitching a ride on a bird or another animal moving into the area. It also could be transported by an animal that already is carrying the disease and infects local ticks, said Dr. David Persing, a former Mayo Clinic tick researcher now with a Seattle biotechnology company.
"You got a cabin ... you got a problem," Persing said.
If left untreated, Lyme disease can cause heart damage, neurological problems and arthritis. Two to 3 percent of those with HGE die of complications, according to the U.S. Centers for Disease Control and Prevention in Atlanta.
About 12,500 cases of Lyme disease are reported each year in the United States, according to the CDC. About 1,000 cases of HGE have been reported in the United States since the disease first was reported by Duluth Dr. Johan Bakken in 1994.
Health officials warn people should stay out of brushy wooded areas, use tick repellent and check often for bites. There also is a Lyme disease vaccine, which the CDC recommends for people ages 15 to 70 who work or spend a significant amount of time in tick-infested areas. Mid-May to mid-July is prime bite time for deer ticks.
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