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Tick-Borne Illnesses

  • Diseases transmitted by ticks that are infected with bacteria, viruses, or parasites
  • Types: Lyme disease, anaplasmosis, babesiosis, Rocky Mountain spotted fever, Powassan virus
  • Treatment includes antibiotics or other medications depending on the type of tick-borne illness
  • Involves infectious diseases, laboratory medicine

Tick-Borne Illnesses


A tick bite can turn a pleasant walk in the woods or an afternoon in the garden into a cause for concern. But being bitten by a tick isn’t a reason for immediate panic. Tick-borne illnesses such as Lyme disease can be treated effectively.

How do you know that you’ve been bitten by a tick?

It can be difficult to know if you’ve been bitten by a tick because the bite doesn’t hurt and you may not even feel it, says emergency medicine expert Harry Moscovitz, MD.

The way to know for sure is to find a tick attached to you. If the tick has fed, it may transmit an infectious agent.

What are some examples of illnesses transmitted by ticks?

There are several tick-borne diseases that range in severity and symptoms.

Lyme disease is caused by the bacterium Borrelia burgdorferi and is transmitted to humans through the bite of infected blacklegged ticks (also known as deer ticks).

Anaplasmosis and ehrlichiosis are two closely related diseases (caused by the bacterium Anaplasma phagocytophilum and Ehrlichia, respectively) that are also transmitted to humans by the bite of an infected tick (a deer tick, in the case of anaplasmosis, or a lone star tick, in the case of ehrlichiosis).

Babesiosis is a malaria-like parasite that infects red blood cells. It typically causes flu-like symptoms but can cause severe and even fatal disease in older people and in those who are immunocompromised.

Rocky Mountain spotted fever is a potentially fatal tick-borne bacterial disease that can be transmitted by the American dog tick, the Rocky Mountain wood tick, and the brown dog tick.

Powassan virus is a rare, potentially serious infection transmitted to humans via the bite of an infected tick. It’s spread by groundhog ticks, squirrel ticks, and deer ticks, which primarily inhabit the Northeast and upper Midwest of the United States. People infected with Powassan virus cannot spread it to others, though it may be transmitted through blood transfusions involving blood donated by an infected individual.

Does a tick bite cause immediate danger?

Once a tick attaches to an individual, it starts feeding—and may stay attached for days. Then, it falls off when it’s full.

The period of time a tick needs to transmit an infection varies depending on the infectious agent. Powassan virus may be transmitted very quickly. To transmit Borrelia burgdorferi, an infected deer tick needs to feed for at least 36 or even 48 hours before the risk of transmission becomes substantial. Studies have found that about 75% of people who recognize a deer tick bite remove the tick in 48 hours or less.

Typically, it is the tick someone doesn’t find that is most likely to transmit the infection. The majority of people who do develop Lyme disease do not recognize the causative tick bite.

Do I need to go to the emergency room if I’m bitten by a tick?

You can remove the tick on your own, without going to the emergency room. Grasp the tick with fine-tipped tweezers as close to the skin as possible and simply pull up until it comes out. If a bit of the tick’s mouthparts are left in the skin, leave them. It’s important to wear latex gloves when touching a tick that may be macerated, or softened.

In the emergency department, doctors will use the soap they use to wash their hands, apply it to a piece of gauze, and rub it in a circle until the tick falls out.

What are the signs of Lyme disease?

It is important to distinguish between symptoms and signs when considering whether a doctor will test a patient for Lyme disease. Symptoms are subjective—fatigue, pain, muscle or joint aches, headache, or perceived cognitive difficulties, for example. Signs, on the other hand, are objective physical findings—a rash, facial nerve palsy, redness, swelling and/or pain on movement of a joint, for example.

While patients with Lyme disease may have a headache, fatigue, or joint pain, these are extremely common symptoms of many conditions, such as viral infections or even stress. If a patient has only non-specific symptoms without any signs of Lyme disease, it is far more likely the cause is something other than Lyme disease.

If antibody tests for Lyme disease are ordered for patients with only subjective symptoms and no signs of Lyme disease, many of the positive results will be “false-positive” results because the specificity of the tests is imperfect. Consequently, with rare exceptions, tests for Lyme disease are generally not be ordered for patients with only non-specific symptoms and no signs of Lyme disease.

One major sign of Lyme disease is the oval red rash known as erythema migrans. The vast majority of people with Lyme disease (at least 90%) will have this rash. It starts as a flat red spot at the site of the tick bite and gets bigger.

If untreated, it typically lasts for weeks and may get very large, up to a couple of feet in diameter. Although it commonly is thought to be a “bullseye” rash, it more commonly remains uniformly red—although there is often more intense redness in the center of the rash.

Later-stage signs of Lyme disease can include additional rashes, arthritis with joint swelling (the knee is the joint most commonly involved), facial nerve palsy, an irregular or slow heartbeat (Lyme carditis), or inflammation of the brain or spinal cord.

Check with your doctor if you are concerned that you may have a tick-borne illness. 

How are tick-borne illnesses diagnosed?

Many of these illnesses are associated with abnormal results of a standard blood tests (e.g., low white blood cell count and/or platelet count in Anaplasmosis). For many of these tick-borne illnesses, the diagnosis is made based on specific blood tests.

What is the treatment for tick-borne illness?

  • Lyme disease: Patients with Lyme disease who are treated with appropriate antibiotics usually recover rapidly and completely. Antibiotics commonly used include doxycycline, amoxicillin, or cefuroxime axetil.
  • Anaplasmosis, ehrlichiosis and Rocky Mountain spotted fever: Doxycycline is the first line treatment for adults and children of all ages.
  • Babesiosis: Combination therapy with atovaquone and azithromycin is most commonly recommended for treatment of mild to moderate babesiosis. Treatment is usually continued for 7 to 10 days. A combination regimen of oral clindamycin and quinine has also been proven effective, but the rate of adverse reactions is significantly higher with this combination.
  • Powassan virus: There are no medications for treating Powassan virus infections. Medications, however, can help to relieve symptoms and prevent complications. People with severe disease are typically treated in a hospital where they may be given intravenous fluids, fever-reducing medications, breathing support, and other therapies as needed.

What makes Yale Medicine's approach to tick-borne illnesses unique?

Yale Medicine specialists are at the forefront of treatment for tick-borne illnesses, including Lyme disease. "Yale is the place to go where patients can get that full range of appropriate tests as well as admission to the Yale New Haven Hospital, if needed,” says Dr. Moscovitz.

Our emergency department doctors understand concerns about tick bites and treat patients with care and attention.

“If you can't get to your doctor because it's Friday night, come on into the ER and we'll evaluate you and get you started,” Dr. Moscovitz says. “That's better than waiting until Monday.”