What is Lyme disease?
Lyme disease is a disease caused by a type of bacteria called Borrelia burgdorferi, which can be transmitted through the bite of an infected black-legged tick. Typical symptoms include a characteristic "bull's-eye" (target)-shaped rash that is at least 5 cm in diameter, along with fever, headache, and muscle or joint pain. Not everyone with Lyme disease will develop a rash, although sometimes multiple "bull's-eye" rashes will occur. Lyme disease can be successfully treated with antibiotics, but if left untreated, later symptoms can include recurring joint pain and swelling, heart disease, and nervous system disorders.
Where is Lyme disease found?
Although Lyme disease is the most commonly-reported tick-borne disease in the United States, it is rare in Washington State. Each year, 10-40 cases of Lyme disease among Washington residents are reported, but most of these people acquire the disease following tick bites that occur in the northeast and upper mid-west states, where Lyme disease occurs more commonly. Only zero to seven confirmed Lyme disease cases per year are reported to be acquired in Washington.
In Washington, the ticks that spread Lyme disease are primarily found in western Washington, but are also present on the eastern slopes of the Cascades.
In North America, most Lyme disease cases occur between May and August.
How is Lyme disease spread?
People can become infected if they are bitten by a black-legged tick that is carrying Borrelia burgdorferi; these ticks usually need to remain attached to a person for at least 36 hours to transmit the bacteria. These ticks live in forested or brushy areas and perch on tips of grasses or shrubs, then climb onto people or animals that brush by. They then crawl until they find a suitable place to bite. Ticks can bite any skin on the human body, but are often found in hard-to-see areas, such as the groin, armpits, or scalp.
Black-legged ticks pick up the bacteria after feeding on infected rodents. On the Pacific Coast, the western black-legged tick (Ixodes pacificus) spreads Lyme disease. Both the western black-legged tick and the black-legged tick responsible for spreading Lyme disease in the northeastern, mid-Atlantic, and north-central United States (Ixodes scapularis), are also called deer ticks.
There is no evidence that Lyme disease can be passed from one person to another through touching, kissing, or sex. While dogs and cats can also get Lyme disease, there is no evidence that they can spread the disease directly to their owners. However, pets can transport infected ticks that then attach onto humans.
What are the symptoms of Lyme disease?
Untreated Lyme disease can produce a wide range of symptoms, depending on the stage of infection. Early signs of Lyme disease include fever, chills, headache, fatigue, muscle and joint aches, swollen lymph nodes, and erythema migrans (EM) rash. The EM rash is the most distinctive sign of Lyme disease – it is often “bull's-eye” (target)-shaped and at least 5 cm in diameter. This type of rash occurs in 70-80 percent of infected persons. The rash usually begins at the site of a tick bite 3-30 days after the bite, and expands outward gradually over a period of days. Not everyone with Lyme disease will develop a rash, but sometimes multiple rashes will occur. Rashes that appear within 36 hours of a bite are very unlikely to be due to Lyme disease and are commonly allergic reactions at the site of the tick bite.
Lyme disease can be successfully treated with antibiotics, but if left untreated, later symptoms can include severe headaches, additional EM rashes, recurring joint pain, heart disease, and nervous system disorders.
How can I protect myself and other from Lyme disease?
The best way to protect yourself and others against Lyme disease is by reducing your exposure to ticks and preventing ticks from biting. See this Tick Prevention Poster.
Learn more about prevention on DOH's Tick page.