With spring underway, tick season will soon come with it, and insect surveillance experts in the Twin Cities are predicting Minnesota could experience a high number of Lyme disease cases and other tick-borne diseases.

Metropolitan Mosquito Control District (MMCD), which monitors tick presence in the Twin Cities metro area, saw a thriving population of deer ticks last year, according to public affairs manager Alex Carlson.

MMCD monitors tick presence by catching mice, a common host for the deer tick, and measuring how many ticks are on them, Carlson said. Last summer, MMCD saw record-high numbers of ticks per mouse, especially in early August.

Based on last year, MMCD expects ticks to be “out in abundance,” Carlson said.

May and June are the peak months of transmission for Lyme disease, which is transmitted by deer tick bites, Carlson said. At this time, ticks are in the nymphal stage, meaning they are small and difficult to spot. If not spotted and removed, ticks will stay attached long enough to transmit the bacteria that causes Lyme disease.

Despite May and June having the highest rate of transmission per month, ticks emerge from the ground as soon as the snow recedes, according to Benjamin Clarke, a professor at the University of Minnesota Medical School who studies Lyme disease.

Clarke said in an email to the Minnesota Daily the estimated number of new Lyme disease cases is “enormous,” more 350,000 annually.

What is Lyme disease?

Lyme disease is an inflammatory response to the bacteria Borrelia burgdorferi, Clarke said. The only way to get exposed to the bacteria is through a tick bite, introducing the bacteria into the host’s skin as the tick feeds.

The first sign of Lyme disease is a bulls-eye rash at the sight of the tick bite, Clarke said. Subsequent symptoms include headache, nausea, achy joints and muscles, and cognitive difficulties.

If Lyme disease is caught and treated with antibiotics early in the infection, the patient has a good chance of a full recovery, Clarke said. If Lyme disease is not treated early, it can cause more severe, chronic problems such as arthritis, brain swelling and nerve damage.

“Treatment with antibiotics later than a couple of weeks [into the infection] risks the chance of a more severe problem of infections in the joints, brain and heart,” Clarke said. “In general, long-term problems from Lyme disease are not lethal, but the patient is plagued with numerous chronic miserable problems.”

Why is there an increase in Lyme disease cases?

Lyme disease cases increase as the tick population grows, according to University tick-borne disease researcher Jonathan Oliver.

“In general, we are seeing a big expansion in the range of the deer tick, which carries most of the human diseases in the U.S.,” Oliver said. “As the deer tick range is expanding, we are seeing an expansion of all associated with it.”

The cause of this expansion is unknown, but climate change likely plays a role by allowing ticks to survive farther north, according to Oliver.

He said the tick population in pre-existing habitats has increased, likely due to changes in ground cover, land use and animal host patterns.

“We are seeing increases in the density of ticks in their forested habitats, beyond what it used to be in some cases, far beyond what it used to be,” Oliver said. “In many areas, there used to be no ticks.”

The proportion of ticks that are infected with the Lyme disease-causing bacteria has increased in recent years, Oliver said. About 33-50% of adult deer ticks and 25-33% of tick nymphs carry the bacteria.

How to protect yourself

The best way people can protect themselves from Lyme disease is by being aware of when ticks are out and when they are entering areas with ticks, according to Oliver. It takes at least 24 hours of the tick feeding to transmit the bacteria that causes Lyme disease.

Checking for ticks after being in an area where ticks are prevalent is also important, Oliver said. Ticks are prevalent in wooded, brushy and grassy areas. Oliver said using insect repellent that contains DEET is effective in repelling ticks.

Additionally, Carlson said people can help reduce the number of ticks in their yard by keeping their grass short and reducing overgrown vegetation on their property lines.