TICK BITE OVERVIEW
There are many different types of ticks in the United States, some of which are capable of transmitting infections. The risk of developing these infections depends upon the geographic location, season of the year, type of tick, and, for Lyme disease, how long the tick was attached to the skin.
While many people are concerned after being bitten by a tick, the risk of acquiring a tick-borne infection is quite low, even if the tick has been attached, fed, and is actually carrying an infectious agent. Ticks transmit infection only after they have attached and then taken a blood meal from their new host. A tick that has not attached (and therefore has not yet become engorged from its blood meal) has not passed any infection. Since the deer tick that transmits Lyme disease must feed for >36 hours before transmission of the spirochete, the risk of acquiring Lyme disease from an observed tick bite, for example, is only 1.2 to 1.4 percent, even in an area where the disease is common.
The organism that causes Lyme disease, Borrelia burgdorferi, lies dormant in the inner aspect of the tick's midgut. The organism becomes active only after exposure to the warm blood meal entering the tick's gut. Once active, the organism enters the tick's salivary glands. As the tick feeds, it must get rid of excess water through the salivary glands. Thus, the tick will literally salivate organisms into the wound, thereby passing the infection to the host.
If a person is bitten by a deer tick (the type of tick that carries Lyme disease), a healthcare provider will likely advise one of two approaches:
- Observe and treat if signs or symptoms of infection develop
- Treat with a preventive antibiotic immediately
There is no benefit of blood testing for Lyme disease at the time of the tick bite; even people who become infected will not have a positive blood test until approximately two to six weeks after the infection develops (post-tick bite).
The history of the tick bite will largely determine which of these options is chosen. Before seeking medical attention, the affected person or household member should carefully remove the tick and make note of its appearance (picture 1). Only the Ixodes species of tick, also known as the deer tick, causes Lyme disease.
HOW TO REMOVE A TICK
The proper way to remove a tick is to use a set of fine tweezers and grip the tick as close to the skin as is possible. Do not use a smoldering match or cigarette, nail polish, petroleum jelly (eg, Vaseline), liquid soap, or kerosene because they may irritate the tick and cause it to behave like a syringe, injecting bodily fluids into the wound.
The proper technique for tick removal includes the following:
- Use fine tweezers to grasp the tick as close to the skin surface as possible.
- Pull backwards gently but firmly, using an even, steady pressure. Do not jerk or twist.
- Do not squeeze, crush, or puncture the body of the tick, since its bodily fluids may contain infection-causing organisms.
- After removing the tick, wash the skin and hands thoroughly with soap and water.
- If any mouth parts of the tick remain in the skin, these should be left alone; they will be expelled on their own. Attempts to remove these parts may result in significant skin trauma.
AFTER THE TICK IS REMOVED
Tick characteristics — It is helpful if the person can provide information about the size of the tick, whether it was actually attached to the skin, if it was engorged (that is, full of blood), and how long it was attached.
- The size and color of the tick help to determine what kind of tick it was (picture 1 and figure 1);
- Ticks that are brown and approximately the size of a poppy seed or pencil point are deer ticks. These can transmit Borrelia burgdorferi (the bacterium that causes Lyme disease) and a number of other tick-borne infections, including babesiosis and anaplasmosis. Borrelia burgdorferi infected deer ticks live primarily in the northeast and mid-Atlantic region (Maine to Virginia) and in the midwest (Minnesota and Wisconsin) region of the United States, and less commonly in the western US (northern California).
- Ticks that are brown with a white collar and about the size of a pencil eraser are more likely to be dog ticks (Dermacentor species). These ticks do not carry Lyme disease, but can rarely carry another tick-borne infection called Rocky Mountain spotted fever that can be serious or even fatal.
- A brown to black tick with a white splotch on its back is likely a female Amblyomma americanum (Lone Star tick; named after the white splotch) (picture 2). This species of tick has been reported to spread an illness called STARI (southern tick-associated rash illness). STARI causes a rash that is similar to the erythema migrans rash, but without the other features of Lyme disease. Although this rash is thought to be caused by an infection, a cause for the infection has not yet been identified. This type of tick can also carry and transmit another infection called human monocytic ehrlichiosis.
- A tick that was not attached, was easy to remove or just walking on the skin, and was still flat and tiny and not full of blood when it was removed could not have transmitted Lyme disease or any other infection since it had not yet taken a blood meal.
- Only ticks that are attached and have finished feeding or are near the end of their meal can transmit Lyme disease. After arriving on the skin, the tick that spreads Lyme disease usually takes 24 hours before feeding begins.
- Even if a tick is attached, it must have taken a blood meal to transmit Lyme disease. At least 36 to 48 hours of feeding is required for a tick to have fed and then transmit the bacterium that causes Lyme disease. After this amount of time, the tick will be engorged (full of blood). An engorged tick has a globular shape and is larger than an unengorged one.
- It is not clear how long a tick needs to be attached to transmit bacteria other than Borrelia burgdorferi.
Need for treatment — The clinician will review the description of the tick, along with any physical symptoms, to decide upon a course of action. The Infectious Diseases Society of America (IDSA) recommends preventive treatment with antibiotics only in people who meet ALL of the following criteria:
- Attached tick identified as an adult or nymphal I. scapularis (deer) tick
- Tick is estimated to have been attached for ≥36 hours (based upon how engorged the tick appears or the amount of time since outdoor exposure)
- The antibiotic can be given within 72 hours of tick removal
- The local rate of tick infection with B. burgdorferi is ≥20 percent (known to occur in parts of New England, parts of the mid-Atlantic states, and parts of Minnesota and Wisconsin)
- The person can take doxycycline (eg, the person is not pregnant or breastfeeding or a child <8 years of age)
If the person meets ALL of the above criteria, the recommended dose of doxycycline is a single dose of 200 mg for adults and 4 mg/kg, up to a maximum dose of 200 mg, in children ≥ 8 years.
If the person cannot take doxycycline, the IDSA does not recommend preventive treatment with an alternate antibiotic for several reasons: there are no data to support a short course of another antibiotic, a longer course of antibiotics may have side effects, antibiotic treatment is highly effective if Lyme disease were to develop, and the risk of developing a serious complication of Lyme disease after a recognized bite is extremely low.
MONITORING FOR LYME DISEASE
Many people have incorrect information about Lyme disease. For example, some people are concerned that Lyme disease is untreatable if antibiotics are not given early (this is untrue; even later features of Lyme disease can be effectively treated with appropriate antibiotics). Many local Lyme disease networks and national organizations disseminate unproven information and should not be the sole source of education about Lyme disease. Reputable sources are listed below (see 'Where to get more information' below).
Signs of Lyme disease — Whether or not a clinician is consulted after a tick bite, the person who was bitten (or the parents, if a child was bitten) should observe the area of the bite for expanding redness, which would suggest erythema migrans (EM), the characteristic rash of Lyme disease (picture 3). (See "Patient information: Lyme disease symptoms and diagnosis (Beyond the Basics)".)
The EM rash is usually a salmon color although, rarely, it can be an intense red, sometimes resembling a skin infection. The color may be almost uniform. The lesion typically expands over a few days or weeks and can reach over 20 cm (8 inches) in diameter. As the rash expands, it can become clear (skin-colored) in the center. The center of the rash can then appear a lighter color than its edges or the rash can develop into a series of concentric rings giving it a "bull's eye" appearance. The rash usually causes no symptoms, although burning or itching has been reported.
In people with early localized Lyme disease, EM occurs within one month of the tick bite, typically within a week of the tick bite, although only one-third of people recall the tick bite that gave them Lyme disease. Components of tick saliva can cause a short-lived (24 to 48 hours) rash that should not be confused with EM. This reaction usually does not expand to a size larger than a dime.
Approximately 80 percent of people with Lyme disease develop EM; 10 to 20 percent of people have multiple lesions. If EM or other signs or symptoms suggestive of Lyme disease develop (table 1), the person should see a healthcare provider for proper diagnosis and treatment. (See "Patient information: Lyme disease treatment (Beyond the Basics)".)
WHERE TO GET MORE INFORMATION
Your healthcare provider is the best source of information for questions and concerns related to your medical problem.
This article will be updated as needed on our web site (www.uptodate.com/patients). Related topics for patients, as well as selected articles written for healthcare professionals, are also available. Some of the most relevant are listed below.
Patient level information — UpToDate offers two types of patient education materials.
The Basics — The Basics patient education pieces answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials.
Patient information: Lyme disease (The Basics)
Patient information: Insect bites and stings (The Basics)
Patient information: Rocky Mountain spotted fever (The Basics)
Beyond the Basics — Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are best for patients who want in-depth information and are comfortable with some medical jargon.
Patient information: Lyme disease prevention (Beyond the Basics)
Patient information: Lyme disease symptoms and diagnosis (Beyond the Basics)
Patient information: Lyme disease treatment (Beyond the Basics)
Professional level information — Professional level articles are designed to keep doctors and other health professionals up-to-date on the latest medical findings. These articles are thorough, long, and complex, and they contain multiple references to the research on which they are based. Professional level articles are best for people who are comfortable with a lot of medical terminology and who want to read the same materials their doctors are reading.
Clinical manifestations of Lyme disease in adults
Diagnosis of Lyme disease
Evaluation of a tick bite for possible Lyme disease
Epidemiology of Lyme disease
Musculoskeletal manifestations of Lyme disease
Prevention of Lyme disease
Treatment of Lyme disease
The following organizations also provide reliable health information.
- National Library of Medicine
(www.nlm.nih.gov/medlineplus/lymedisease.html, available in Spanish)
- National Institute of Allergy and Infectious Diseases
- National Center for Infectious Diseases
Division of Vector-Borne Infectious Diseases
- American Lyme Disease Foundation, Inc.