A tick resting on a blade of grass.

Tick-borne illnesses, especially Lyme disease, are on the rise, according to new data out today from the Centers for Disease Control and Prevention.

The number of tick-borne illnesses has more than doubled since 2004. Cases of Lyme—by far the most common—have also nearly doubled since then, to 36,429 reported cases in 2016.

But CDC experts believe the actual number of Lyme infections is much higher—perhaps totaling as many as 300,000 a year, says Lyle Petersen, M.D., M.P.H., director of the CDC’s Division of Vector-Borne Diseases, who spoke at a media briefing today.

Tick-borne diseases are also occurring in an increasingly wide area, Petersen says. Part of the reason may be warmer weather, he says, which lengthens the season when ticks are active.

Another factor, according to Thomas Mather, Ph.D., director of the University of Rhode Island’s Center for Vector-Borne Disease (who was not involved in the new study), may be the increasing geographic spread of deer, which often carry the disease-carrying ticks. As ticks spread geographically, more people come into contact with them, increasing the odds that they, too, will be bitten and infected.

Lyme disease, which causes fever, aches, and often a characteristic bull’s-eye rash, is the most prevalent of tick-borne illnesses in the U.S. If it is left untreated with antibiotics (from one to four months postbite), the bacteria can spread to the muscles, joints, heart, and brain.

Cases of other tick-borne infections, such as Rocky Mountain spotted fever, anaplasmosis, and the rare but deadly Powassan virus (which can cause inflammation in the brain), have also trended upward, according to the CDC’s report.

While the CDC report concludes that the development of vaccines and improved insect-control programs throughout the U.S. could help reduce this growing problem, consumers themselves can follow precautions, such as using insect repellents and treating their backyards with insecticides, to help reduce the risk of bites.

Mosquito Threat Also Increasing

In addition to tick diseases, mosquito-borne infections have increased, according to the CDC report. Those numbers, however, have fluctuated over the years due to epidemics such as the Zika outbreak of 2016.

More on ticks and mosquitos

The report also mentions new illnesses emerging regularly during the past 14 years. “A number of new germs spread through mosquito or tick bites have been introduced here,” says Robert Redfield, M.D., CDC director, who spoke at the briefing. Nine new “vector” diseases have been reported in the U.S. since 2004. The most well-known is Zika, but seven of the others are transmitted by ticks, such as the Heartland virus and Bourbon virus, which can both cause fever, headaches, and fatigue.

Mather says that it’s reasonable to expect more new tick-borne diseases to emerge as different species of ticks spread geographically. When ticks encounter new populations of animals, they can pick up germs the animals have and spread them—for the first time—to humans. “Now, probably more than ever, people have to wonder, just what that tick potentially gave to me,” Mather says.

The CDC’s Petersen says experts are not yet able to predict how severe this coming tick and mosquito season will be: Much will depend on how hot—and thus friendly to disease-carrying insects—temperatures will get this summer and fall. “We know that we just need to be prepared for whatever might occur,” he says.

How to Protect Yourself

The CDC’s new research is concerning, says Michael Hansen, Ph.D., Consumer Reports’ senior scientist, “and it suggests that ticks could be a more serious problem in the future,” he says. “That’s why consumers should be taking control in their own yards and taking actions to reduce the risk of exposure to ticks.”

Here’s what to do:

Get dressed to protect. If you plan to be outside in an area known to be infested with ticks, wear long pants, long sleeves, and socks. Tuck your shirt into your pants and your pant legs into your socks. Once back inside, check your clothing and body for ticks. If you find one, use our guide to removing it.

Use the right bug repellent. Check Consumer Reports’ ratings to find the insect repellents that are most effective. In our tests, we’ve found that some products containing 15 to 30 percent deet, 20 percent picaridin, or 30 percent oil of lemon eucalyptus were all effective against both mosquitoes and ticks.

Bugproof your yard and your pets. To make your yard less appealing to ticks, keep your grass mowed. And because ticks love shade, remove any leaves or other debris and keep brush trimmed. You can also try using tick bait boxes, which work by attracting rodents that carry ticks and applying tick-killing insecticide to them. To reduce the number of mosquitoes in and around your yard, regularly look for—and drain away—any standing water. Check places such as gutters, birdbaths, wheelbarrows, and swimming pool covers. Check your outdoor pets daily for ticks, and consider using an anti-tick collar, medication, shampoo, or other product.

How to Keep Ticks out of Your Yard

Ticks love tall grass and cool, damp areas. On the "Consumer 101" TV show, Consumer Reports expert Catherine Roberts explains how to make your yard less inviting to these pests.