Ticks are notorious for transmitting Lyme disease, but did you know these tiny arachnids can cause more than a dozen other illnesses in humans? With cases of Lyme and other tick-borne diseases on the rise over the past quarter century, the threat to public health is real. At the same time, you need to put the risk of tick bites into perspective, and take preventive measures, Andrea Swei, PhD, associate professor in the department of biology at San Francisco State University, tells Health. “It’s important to stay informed but not panic,” she says.
What is a tick-borne illness?
Ticks are vectors, meaning they’re capable of carrying and transmitting disease. You can contract a tick-borne disease through a tick bite, but not all tick-borne illnesses affect people. Only certain tick species bite and infect humans, says the Centers for Disease Control and Prevention (CDC). Likewise, different species can transmit different diseases, so patterns of illness vary widely from one region of the country to another. “You’re not going to have equal risk in every location,” according to Swei.
There may be as many 300,000 to 400,000 new cases of Lyme disease in the US each year, making it the most common tick-borne illness in America. Lyme is common in the Northeast and Upper Midwest as well as the Pacific Coast.
How do ticks infect humans?
Ticks feed on the blood of birds, reptiles, amphibians, and mammals—including people—throughout their various life stages. If a host animal has a blood-borne infection, the tick can ingest that pathogen during its blood meal. When the tick attaches to a human, that infection-causing bacterium, virus, or parasite can be passed along as the little bloodsucker engorges its body with your blood.
“Ticks are dirty, and they really do have a lot of bugs,” Christine Green, MD, a family physician in Mountain View, California, and a member of the Bay Area Lyme Foundation’s scientific advisory board, tells Health.
Here are several common, emerging, and rare-but-concerning tick-borne infections you should know about.
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Anaplasmosis
This is a bacterial infection caused by Anaplasma phagocytophilum. The disease is transmitted by the blacklegged tick (Ixodes scapularis), also known as a deer tick, in the Northeastern US and Upper Midwest, says the CDC. The Western blacklegged tick (Ixodes pacificus) transmits the bug on the Pacific Coast. “People with anaplasma can have high fevers; they can be pretty sick,” Jennie Johnson, MD, an attending physician of infectious diseases at Lifespan in Providence, Rhode Island, tells Health. They can develop a rash, she says, but it’s more like a “diffuse rash all over the body.”
Babesiosis
Babesiosis is primarily found in the Northeast and Upper Midwest regions. It is a parasitic infection caused by Babesia transmitted to humans by the blacklegged tick. “You don’t really get a rash with it, except maybe at the tick bite, and it’s accompanied by really severe fatigue,” observes Swei, who studies vector-borne diseases.
Borrelia miyamotoi disease
Borrelia miyamotoi bacteria were first identified in Japan in 1995. In the US, they are transmitted by the blacklegged tick and Western blacklegged tick. People with B. miyamotoi disease may experience fever, chills, and headache, says the CDC. Rash is less common.
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Colorado tick fever
This rare illness is transmitted by infected Rocky Mountain wood ticks (Dermacentor andersoni). Westerners living in the Rocky Mountain states at 4,000 to 10,000 feet above sea level may be at risk of contracting Colorado tick fever (CTF) virus.
Ehrlichiosis
The lone star tick (Amblyomma americanum) is responsible for transmitting Ehrlichia bacteria, the cause of this infection. Ehrlichiosis primarily affects people in the Southeast and south central states. Some people have symptoms so mild that they don’t require any treatment, while others can become severely ill, says Mayo Clinic. One species of bacteria, Ehrlichia chaffeensis, can be fatal if untreated, according to the CDC.
Lyme disease
Lyme disease gets its name from the town in Connecticut where it was first described. It’s a bacterial infection transmitted by blacklegged ticks in the northeastern US and Upper Midwest and by western blacklegged ticks along the Pacific Coast. These Borrelia infections can produce a red, circular rash that expands over time. Fever, fatigue, muscle aches, and joint pain are just a few of the earlier symptoms of the illness.
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Powassan virus disease
Powassan virus is rare but serious. It can cause swelling of the brain and the membranes around the brain and spinal cord. “Not only is it fatal, but it can be transmitted very, very quickly by a biting tick,” says Swei. Powassan virus can be transmitted in a matter of minutes, she explains, whereas Lyme takes at least 36 hours from tick bite to transmission. This disease has been reported in the Northeast and Great Lakes regions, notes CDC.
Rocky Mountain spotted fever
As its name implies, Rocky Mountain spotted fever produces a dot-like rash, resembling measles, and it can be fatal if left untreated. The culprit? Rickettsia rickettsii bacteria. It can transmitted by the American dog tick (Dermacentor variabilis) in the Eastern, Central, and Western US; the Rocky Mountain wood tick in the Rocky Mountain states; and the Brown dog tick (Rhipicephalus sanguineus ) at the US-Mexican border. It is the most common and series illness in a group of diseases known as spotted fever group rickettsioses, says the CDC. San Francisco State’s Swei says Rocky Mountain spotted fever has recently appeared in impoverished areas of the Southwest where ticks can enter and live in people’s homes.
Southern tick-associated rash illness (STARI)
Like Lyme disease, STARI can produce a red, bulls-eye rash and other Lyme-like symptoms. But the vector is different. STARI is transmitted by the lone star tick. And the cause remains unknown. “We know it’s not caused by Borrelia burgdorferi,” the pathogen responsible for most cases of Lyme, John Aucott, MD, director of the Johns Hopkins Lyme Disease Clinical Research Center in Baltimore, tells Health.
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Tick-borne relapsing fever (TBRF)
Soft ticks of the genus Ornithodoros transmit certain Borrelia bacteria that cause TBRF. The illness, which triggers a high fever, is found primarily in Western states. “Cases of TBRF are quite rare,” with fewer than 20 per year, according to a review of tick-borne diseases in the journal Clinical Chemistry.
Tularemia
There are a number of ways humans can contract tularemia, a bacterial infection caused by Francisella tularensis. Bites by dog, wood, and lone star ticks can put you at risk. (So can handling sick or dead animals with the infection, says the CDC.) Symptoms depend on how the infection enters a person’s body. You might develop a skin ulcer, fever, or swollen glands.
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