Ticks are back, and with them the risk of Lyme disease.

In Washington and most of the U.S., the peak tick season is spring and summer—roughly May through July or August. Ticks that attach themselves to bodies can infect people with a bacteria that causes Lyme disease. The illness is characterized initially by a rash, headache, fever, and chills, and in the worst cases by arthritis, facial palsy, and impaired memory.

The national Centers for Disease Control estimates that 476,000 people in the U.S. are diagnosed with the disease each year. There is no vaccine against it.

Pets (though rarely cats) can also get the disease. If left untreated, dogs can experience heart complications, joint inflammation, and permanent nervous system damage. But most dogs are able to fight off the infection themselves without serious illness, according to Blue Pearl Pet Hospital, whose Washington locations include Lakewood, Renton and Seattle.

In Washington, ticks carrying the bacteria that causes Lyme disease are most common west of the Cascade Mountains. People and pets can avoid them by avoiding grassy patches and high-growth vegetation when hiking or in wooded areas.