This year, people are seeking emergency care for tick bites in the highest level since 2017, according to data from the US Centers for Disease Control and Prevention, and reported cases of Lyme disease have continued to rise through the years.

Experts say the increases are driven by warmer temperatures due to climate change and the expanding presence of ticks in more areas in the US and Canada — including places where people are less familiar with the risks and how to prevent disease.

“When we first started doing this [in the mid-1980s], there were very few cases of Lyme disease reported in Canada. Lyme disease is pretty well established in Canada at this point,” said Dr. Thomas Daniels, the director of the Louis Calder Center, Fordham University’s biological field station.

Lyme disease-carrying deer ticks are mostly active when temperatures are above 45 degrees Fahrenheit, and they thrive in areas with at least 85% humidity, according to the US Environmental Protection Agency.

“It likes to be in humid areas, not wet areas, but humid areas,” said Daniels. “If you sample on a lawn that gets baked in the sun all day, you’re not going to find ticks. You go 20 feet into the woods where it’s shady and the temperature’s generally lower and there’s more ground cover, you will find ticks.”

The threat from ticks and mosquitoes, which drive transmission of diseases such as West Nile, dengue and malaria, is already increasing.

“Because of increases in temperature that we’ve already seen, because of human impacts on the climate, the temperature is already getting more suitable for transmission of disease here in the United States and North America,” Dr. Erin Mordecai, an associate professor of biology at Stanford University, said at a news briefing on Monday.

And while climate change is contributing to the expansion of tick habitats, it’s not the sole driver. Human changes to landscapes also shape where ticks are found.

“It’s never just one factor, right?” Dr. Jean Tsao, a professor at Michigan State University who studies disease ecology, said at a news briefing. “In the continental US, most of the changes in the range is probably due to land use change affecting wildlife communities. Also management of wildlife populations, such as the white-tailed deer. That plays a major role for many of these ticks.”

What is Lyme disease?

Deer ticks, also known as black-legged ticks, are the primacy ticks that carry Lyme disease. During the nymph stage, when they are most active, the ticks are about the size of a poppy seed and are easy to miss. As they feed on blood, they can transmit pathogens, including the bacterium Borrelia burgdorferi, which causes Lyme disease. This transmission occurs through the tick’s saliva, which enters the host’s bloodstream during feeding.

Brian Fallon, director of the Lyme and Tick-Borne Diseases Research Center at Columbia University, told CNN on Friday that infection can cause a range of multisystem symptoms. Once in the bloodstream, the bacteria can go to various parts of the body including the heart, central nervous system, the brain or peripheral nerves.

“Most people think of the Lyme rash as a bull’s-eye target rash. In fact, that’s not the most common presentation,” said Fallon. “The most common presentation is more of a pinkish, reddish rash. But the main thing is that it expands in size from a small rash to five centimeters or larger.”

Fallon notes that some people may also see more than one rash on different parts of their body. As the disease develops without treatment, more serious symptoms may emerge. Symptoms may last for months or even years, said Fallon.

“It’s recognized mainly by the rash early on, if you’re lucky enough to see it, and then later, by symptoms such as the neurologic symptoms that may manifest as a facial palsy or a meningitis causing severe headaches with stiff neck or shooting pains or severe stabbing pains,” Fallon said. There may be cardiac symptoms such as palpitations or slow rhythms; muscle pain and fatigue.

“It can be profoundly debilitating,” he said.

Protective measures are ‘not fool-proof’

Daniels says that although there are measures that can be taken to decrease the likelihood of a tick bite, prevention methods are not foolproof. The most important protection against Lyme disease is tick removal as soon as possible, he said.

“The key is to get the tick off you as quickly as possible. None of these [tick-borne] pathogens are transmitted very quickly, except for Powassan virus, which can be transmitted in as little as 15 minutes. But the infection rate for [humans] is very, very low,” said Daniels. “For Lyme disease, you’ve got a 24 to 48 hour window of opportunity there to get the tick off, because it takes some time for the tick to gear up through its feeding to actually transmit the bacteria.”

Daniels advises people to wear more clothes in the summertime. “The longer we can keep the tick on the outside of our bodies and not on our skin, the less likely it is to find a place to attach.” Clothes can also be treated with permethrin, an insecticide that repels ticks.

When hiking, Fallon advises people to stay on the trail, as ticks roam in leafy areas and wood piles. Daniels advises people to conduct a “tick check” for themselves and each other if they’re in an area with ticks.

“It’s helpful because the ticks may go behind your knee, or they may go and bite you in the back, and you can’t see your back or reach your back. Take a shower at the end of the day, because that may help to wash off some ticks that haven’t fully attached yet,” he said.

If a tick is attached for a prolonged period of time, Fallon says that it would gradually “blow as big as a raisin” from continuously sucking blood. If you do find a tick, experts advise people to use tweezers to take out the tick from underneath its body.

“Don’t try to burn it off with a cigarette. Don’t try to put anything toxic on it. Remove it with a tweezer,” he said.