Ticks and Tick-Borne Diseases: Slideshow

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Ticks are the most common vectors for vector-borne diseases in the United States. In North America, tick bites can cause Lyme disease, human granulocytic and monocytic ehrlichiosis, babesiosis, relapsing fever, Rocky Mountain spotted fever, Colorado tick fever, tularemia, Q fever, and tick paralysis. Europe has a similar list of illnesses caused by ticks, but additional concerns include boutonneuse fever and tick-borne encephalitis. Lyme disease is one of the most prominent tick-borne diseases, and its main vector is the tick genus Ixodes, primarily Ixodes scapularis. Image courtesy of the US Centers of Disease Control and Prevention.

Lyme disease is a systemic infection caused by the spirochete Borrelia burgdorferi. The pathophysiology of Lyme disease is incompletely understood. The bacteria are inoculated into the skin by a tick bite, nearly always from hard-bodied ticks of the genus Ixodes. The primary manifestations of Lyme disease are neurologic and rheumatic in nature. The typical rash of Lyme disease is termed erythema migrans, the bull's eye rash of Lyme disease. However, this dermatologic manifestation does not occur in all patients with Lyme disease (37% noted in one study).

This map demonstrates an approximate distribution of predicted Lyme disease risk in the United States. The true relative risk in any given country compared with other counties may differ from that shown here and may change from year to year. Information on risk distribution within states and counties is best obtained from state and local public health authorities. Map courtesy of the US Centers for Disease Control and Prevention.

The bacterium B burgdorferi (darkfield microscopy technique, 400X; courtesy of the US Centers for Disease Control and Prevention).

Antimicrobial therapy for Lyme disease is based on guidelines produced by the Infectious Diseases Society of America (IDSA). Therapy is divided into oral and parenteral regimens:

Oral therapy: doxycycline 100 mg twice daily, amoxicillin 500 mg 3 times per day, or cefuroxime axetil 500 mg twice daily. Oral macrolides are used as alternatives.
Parenteral therapy: ceftriaxone 2 g once daily. Cefotaxime 2 g 3 times per day or penicillin G 18-24 million U daily are alternatives.

The advantage of doxycycline is that it concomitantly treats other tick-borne infections, such as human granulocytic anaplasmosis. Doxycycline should be avoided in pregnant women. Treatment regimens are based on the extent of disease:

Erythema migrans: oral therapy for 14-21 days;
Meningitis or radiculopathy: parenteral therapy for 10-28 days;
Cranial nerve palsy: oral therapy for 14-21 days;
Cardiac disease: oral or parenteral therapy for 14-21 days;
Arthritis: oral therapy for 28 days; and
Recurrent arthritis after neurologic disease: oral therapy for 28 days or parenteral therapy for 14-28 days.

Patients who fail initial therapy should be reevaluated for alternative diagnoses because long-term antibiotic usage for chronic Lyme disease is not recommended.

This is the classic target (or bull's eye) lesion of Lyme disease; this particular pattern is more common in Europe.

Note the raised vesicular center, which is a variant of erythema migrans. The patient had pulled a tick from the left side of his neck 7 days previously.

In general, I scapularis must be attached for 24-48 hours to transmit the spirochete to the host mammal. The nymph on the right is unfed; the other has been feeding for 48 hours. Image by Darlyne Murawski; reproduced with permission.

Prophylactic Lyme disease treatment following a tick bite should be addressed on a case-by-case basis. According to IDSA, only patients who meet all of the following criteria are eligible for treatment: tick identified as I scapularis, tick attached for more than 36 hours, prophylaxis begun within 72 hours of tick removal, bite occurred in an endemic area, and doxycycline is not contraindicated in the patient. Doxycycline as a single dose of 200 mg or 4 mg/kg for children is usually given. Treatment with an alternative antibiotic is not recommended.

Approximate US distribution of I scapularis. Image courtesy of the US Centers for Disease Control and Prevention.

Amblyomma americanum is the tick vector for monocytic ehrlichiosis and tularemia. An adult and a nymphal form are shown (common match shown for size comparison). Image by Darlyne Murawski; reproduced with permission. Ehrlichiosis is a tick-borne infection of the white blood cells caused by Ehrlichia species. Typical symptoms include fever, headache, malaise, and myalgia, and they occur 5-14 days after the tick bite. It is sometimes referred to as "spotless" Rocky Mountain spotted fever. The treatment of choice is doxycycline, 100 mg twice daily, either orally or intravenously for 10 days. This regimen will also treat Lyme disease and the often mistaken Rocky Mountain spotted fever. Rifampin, 200 mg twice daily for 7 days, is a second-line option because chloramphenicol does not treat Ehrlichia chaffeensis. Tularemia is a zoonosis caused by infection with Francisella tularensis. Typical symptoms include fever, lethargy, anorexia, and in some forms, extensive ulcerating lymphadenopathy. With early diagnosis and treatment, mortality is rare (1%). Antibiotic treatment with streptomycin, 1 g intramuscularly twice daily for 10 days, eradicates the bacteria.

Approximate US distribution of A americanum. Image courtesy of the US Centers for Disease Control and Prevention.

The soft-bodied tick of the genus Ornithodoros transmits various Borrelia species that cause relapsing fever. Photo courtesy of Julie Rawlings, MPH, Texas Department of Health. Relapsing fever is characterized by recurrent acute episodes of fever (usually > 39°C). It is a vector-borne illness spread by lice and ticks. The spirochete species Borrelia is responsible. For tick-borne relapsing fever, treatment is with tetracycline, 500 mg orally every 6 hours, or doxycycline, 100 mg orally twice daily, for 10 days. The louse-borne illness usually only requires a single dose of tetracycline or erythromycin, 500 mg orally.

On the right is an I scapularis, the vector for Lyme disease and babesiosis. On the left (the larger one) is a Dermacentor tick, the vector for Colorado tick fever and Rocky Mountain spotted fever (common match shown for comparison). Babesiosis is a malaria-like illness caused by protozoa of the genus Babesia. It is often self-limiting, requiring no treatment. Recommended anti-Babesia therapy is atovaquone, 750 mg orally twice daily, plus azithromycin, 500 mg orally on day one then 250 mg daily, for 7-10 days. Clindamycin plus quinine is less commonly used because of the ototoxicity associated with quinine. Colorado tick fever is a viral infection transmitted by the bite of the wood tick. It occurs almost exclusively in the western United States and Canada. Fever and flulike symptoms are typical. No specific treatment is effective, but antipyretics provide symptomatic relief. Prompt recovery is the expected outcome. Rocky Mountain spotted fever is caused by infection with Rickettsia rickettsii. It is the most common cause of fatal tick-borne disease in the United States, but it is curable. Fever with relative bradycardia is the rule. The rash is the major diagnostic sign, and it occurs in 88% to 90% of patients within 2-6 days of infection. Early antibiotic treatment significantly reduces the mortality rate and doxycycline, 100 mg orally twice daily for 5-7 days, is the drug of choice.

Approximate US distribution of Dermacentor andersoni. Image courtesy of the US Centers for Disease Control and Prevention.

Rhipicephalus ticks are vectors for babesiosis and rickettsial infections, among others. Image courtesy of Dirk M. Elston, MD.

In typical practice, testing ticks for tick-borne infectious organisms is not generally recommended. However, healthcare practitioners should become familiar with the clinical manifestations of tick-borne diseases (eg, Lyme disease, especially those practicing in endemic areas) and maintain a high index of suspicion during warmer months. Ticks can be placed in a sealed container with alcohol if they need to be transported and identified.

A rarely reported noninfectious complication for tick bites is alopecia. It can begin within a week of tick removal and typically occurs in a 3- to 4-cm circle around a tick bite on the scalp. A moth-eaten alopecia of the scalp caused by bites of Dermacentor variabilis (the American dog tick) has also been described. No particular species appears more likely to cause alopecia. Hair regrowth typically occurs within 1-3 months, although permanent alopecia has been observed.

To remove a tick, use fine-tipped forceps and wear gloves. Grasp the tick as close to the skin surface as possible, including the mouth parts, and pull upward with steady, even traction. Do not twist or jerk the tick because this may cause the mouth parts to break off and remain in the skin; however, note that the mouth parts themselves are not infectious. When removing, wear gloves to avoid possible infection. Children, elderly persons, and immunocompromised persons may be at greater risk for infection and should avoid removing ticks if possible.

A common misperception is that pressing a hot match to the tick or trying to smother it with petroleum jelly, gasoline, nail polish, or other noxious substances is beneficial. This only prolongs exposure time and may cause the tick to eject infectious organisms into the body. Additionally, using lidocaine (subcutaneously or topically) may actually irritate the tick and prompt it to regurgitate its stomach contents. Finally, do not squeeze, crush, or puncture the body of the tick because its fluids (saliva, hemolymph, gut contents) may contain infectious organisms.

Once the tick is removed, wash the bite area with soap and water or with an antiseptic to destroy any contaminating microorganisms. Additionally, the person who removed the tick should wash his or her hands.

Tick-borne disease prevention can be divided into environmental and personal measures. Patients exposed to tick-endemic areas should wear long-sleeved, light-colored clothing when outside. Lighter colors allow for easier identification of ticks. Chemical repellents with DEET (N,N-diethyl-3-methylbenzamide) and picaridin are available in numerous over-the-counter skin preparations as sprays or lotions. Permethrin is an acaricide that can be applied to clothing and used in conjunction with chemical repellents. All individuals should perform regular skin checks. Ticks prefer warm, moist areas -- such as the beltline, groin, and axilla -- although in children the hairline is a common site. Environmental prevention involves clearing underbrush and spraying acaricides in the spring around property sites. These measures prevent both mice and ticks from encroaching on properties. Studies involving the treatment of wild deer and mice have not been conclusive in reducing tick-borne diseases in humans. Currently, no Lyme disease vaccines are available in the United States. Lyme disease vaccine (Lymerix™) was discontinued in 2002, so some patients may still have residual protective antibodies. Image courtesy of the National Library of Medicine.