Utah has traditionally been safe from Lyme and many other insect-borne diseases, thanks to its long, cold winters — but appears to be changing.

According to data from the Centers for Disease Control and Prevention, reports of Lyme disease in Utah have been trending upward over the past decade and a half. Confirmed cases jumped more than 500 percent, from just three in 2000 to 19 in 2016.

Most Utahns who contract Lyme disease still get the infection while traveling the East Coast, said Dallin Peterson, an epidemiologist and specialist in insect- and animal-borne diseases for the Utah Department of Health. But, he said, one of the tick species known to carry the bacteria that causes Lyme, the Western black-legged tick, has migrated to Utah.

Traditionally, that species has mostly inhabited Washington, Oregon and California, Peterson said, but recently it appears to be moving east into Idaho and Utah.

Climate change is likely helping to spread disease-carrying insects into the state, which has been relatively free of insect-borne diseases. The ticks that carry Lyme disease have a two-year life cycle, according to Sam LeFevre, manager of the Utah Department of Health’s Environmental Epidemiology Program.

In temperate states, cold winter weather should kill large numbers of young ticks each year. But as average temperatures climb, LeFevre said, more ticks are surviving each winter to breed the following spring.

“Thus,” he said, “we have a population explosion.”

Lyme disease typically starts with a characteristic bull’s-eye rash and flulike symptoms. Left untreated, it can cause chronic fatigue, bouts of arthritis and nerve damage. In some cases, the disease leads to heart palpitations that may require the use of a pacemaker, according to the CDC.

The number of Western black-legged ticks in Utah is thought to still be too low to cause a Lyme disease outbreak, but officials are developing a statewide surveillance system to monitor the pest’s migration.

Lyme isn’t the only disease of concern, Peterson said. Utahns regularly report cases of tick-borne diseases, including Colorado tick fever and Rocky Mountain spotted fever. But the number of those cases has remained relatively steady in recent years.

Mosquito-borne illnesses remain Peterson’s primary concern. West Nile had a particularly big year in 2017 with 62 confirmed cases, he said, and mosquitoes in southern Utah are being monitored for the presence of Saint Louis encephalitis, a viral mosquito-borne disease that causes swelling in the brain and, in severe cases, can result in paralysis, coma and death.

The disease has turned up in Southern California and Nevada and may be headed toward Utah, Peterson said.

Changing climate and its effects on habitats also have introduced new species of wildlife to some areas, LeFevre said, which has encouraged the spread of the ticks. Longer summers could mean more outdoor recreation, increasing the chances humans will come into contact with ticks.

Taken together, these factors increase the likelihood that Lyme-carrying ticks will encounter humans unfamiliar with their risk — a major concern, warns Jay Lemery, who oversees the wilderness and environmental section at the University of Colorado’s School of Medicine.

“That’s the really scary part,” said Lemery, one of the authors of “Enviromedics,” a book on the impacts of climate change on human health. “This historically naive population is now being exposed.”

The tricky thing about Lyme disease, Lemery said, is its “insidious” nature — it doesn’t exhibit the same symptoms in all patients, and it can be difficult to treat when it’s not detected in its early stages.

“That, to me, is one of the big manifestations of risk,” Lemery said. “There are probably not many doctors in Utah who are used to thinking about Lyme disease.”

Lemery advised Utahns to learn to check themselves thoroughly for ticks when they have been in wooded or grassy areas, because tick bites are less likely to transmit diseases if the tick is removed quickly. Lemery said Utahns should be aware that ticks may be much smaller than they anticipate and will hide in skin folds or crevices.

Peterson urged Utahns headed outdoors to wear protective clothing and insect repellent, which will deter both mosquitoes and ticks. Utahns should see their physician if they develop flulike symptoms, a fever or a rash after recreating outdoors.