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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 if caught early. Doctors in the Yale Medicine Emergency Medicine Department treat hundreds of patients each year for tick-borne illnesses, with excellent results.

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. The bite is potentially dangerous if the tick has fed, causing it to become swollen because of ingested blood.

Many people find the tick attached because they'll touch the area and realize it's the tick that's attached there, Dr. Moscovitz says.

What are some examples of illnesses transmitted by ticks?

"If you get a fever in the middle of the summer, which is not cold and flu season, it's a really good idea to see your doctor and consider the possibility that you have a tick-borne illness,” says Dr. Moscovitz.

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.

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 blacklegged or deer tick, in the case of anaplasmosis, or a lone star tick, in the case of ehrlichiosis).

Babesiosis is a parasite that infects red blood cells, causing malaria-like symptoms. In addition to transmission via tick, babesiosis can be transmitted from mother to unborn child or through a contaminated blood transfusion.

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

“If a tick is only on you two or three hours, it probably won't even get a chance to attach and start feeding,” says Dr. Moscovitz.

Once a tick attaches, it starts feeding and stays on you for about 12 or 18 hours and then falls off when it’s full.

A tick has to be attached for a long time–more than 10 hours–to transmit bacteria. “A tick that looks flat and small probably hasn't eaten,” notes Dr. Moscovitz.

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.

"It's pretty easy to remove a tick gently,” says Dr. Moscovitz. “You don't have to yank. You can put some dishwashing liquid on a piece of gauze and rub the tick gently. It will just come out or let go on its own.”

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.

“Some people come in for us to remove it because they're just disgusted,” he says.

If you remove the tick at home, Dr. Moscovitz recommends washing the area and then waiting to see whether the rash or fever that's typical of Lyme disease develops before starting treatment.

What are the symptoms of Lyme disease?

Symptoms will start appearing a few days after a tick bite. Beginning treatment after the very early symptoms of Lyme disease emerge is just as good as starting it immediately after the bite, says Dr. Moscovitz.

One major symptom is the appearance around the bite of an oval red patch that’s larger than the size of a quarter.

“You might see what they call a ‘bull's eye rash,’ which is also usually an oval patch, but there is some clearing in the middle, so it looks more like a bull's eye mark around the edge and then a white area that's darker in the middle,” Dr. Moscovitz says.

Later-stage symptoms can include severe headaches and neck stiffness, additional rashes, arthritis with severe joint pain and swelling, facial or Bell's palsy, pain in tendons, muscles, joints and bones, heart palpitations or an irregular heartbeat (Lyme carditis), dizziness or shortness of breath, inflammation of the brain and spinal cord, nerve pain, numbness, or tingling and problems with short-term memory.

What are symptoms of other tick-borne illnesses?

Symptoms typically begin appearing within 1 to 2 weeks of an infected tick bite. In cases of:

  • Anaplasmosis and ehrlichiosis, symptoms may include fever, headache, muscle pain, malaise, chills, nausea, abdominal pain, cough, confusion, and occasionally, a rash.
  • Babesiosis symptoms are similar to those of Lyme disease but babesiosis more often starts with a high fever and chills. As the infection progresses, patients may develop fatigue, headache, drenching sweats, muscle aches, chest pain, hip pain, and shortness of breath. Babesiosis can be life-threatening to people with no spleen, the elderly, and people with weak immune systems.
  • Rocky Mountain spotted fever (RMSF) symptoms may appear within a few days of a bite. Symptoms include rash, fever, headache, abdominal pain, vomiting, and muscle pain. Rocky Mountain spotted fever can be extremely dangerous due to the risk of damage to the blood vessels.
  • Powassan virus symptoms may begin within a week to five weeks of a tick bite. Fever, weakness, sleepiness, headache, and vomiting are often the first symptoms and may last between 1 to 3 days. In severe cases, Powassan virus infection can cause meningitis (inflammation of the membranes that surround the brain and spinal cord) and encephalitis (inflammation of the brain), which can lead to a range of symptoms including confusion, loss of coordination, seizures (in children), weakness, difficulty understanding speech and/or speaking, tremors, inability to move on one side of the body, and coma.

How are tick-borne illnesses diagnosed?

There are blood tests that are definitive for babesiosis, anaplasmosis, and Lyme disease. But for someone who's never had Lyme disease, there may be a negative result because he or she has not yet generated the telltale antibody.

“Many times, in the emergency room, even if illness is in an early stage, we'll draw a blood test knowing it's probably going to be negative and then start treatment,” says Dr. Moscovitz. “If the case doesn't resolve the way we expect it to and we really need to know what the infection was, we repeat those tests in two or three weeks and see if they turn positive.”

“If you’ve had a fever and some symptoms that might be related to one of these diseases, that's really good evidence that you had a tick-borne illness,” Dr. Moscovitz says. “Just one test when you come in sick is probably not going to resolve the issue.”

What is the treatment for tick-borne illness?

  • Lyme disease: Patients treated with appropriate antibiotics in the early stages of Lyme disease usually recover rapidly and completely, says Dr. Moscovitz. Antibiotics commonly used include doxycycline, amoxicillin, or cefuroxime axetil. Patients with Lyme disease may require follow-up with a specialist, such as a rheumatologist, to treat chronic aches and pains that are due to inflammation.
  • 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.”