Tick-Borne Infections

HIGH-YIELD FACTS

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Children may be at higher risk for tick-borne infections than adults due to outdoor activities and potentially not noting attached ticks as readily as adults.
The most common tick-borne infection in the United States is Lyme disease, seen most frequently along the Atlantic seaboard and the upper Midwest.
The most common symptom of early localized Lyme disease is the erythema migrans (EM) (target) rash, which occurs within the first 2 weeks after the bite, at which time the antibody response is still negative (making localized Lyme a clinical diagnosis).
Early disseminated Lyme disease occurs in approximately 15% of children several weeks after the tick bite. The most common symptom is multiple EM lesions; other manifestations can include facial nerve or other cranial nerve palsies and lymphocytic meningitis. Carditis is rare in children. Late Lyme disease can be seen as a complication of untreated early-stage Lyme. The most common symptom is relapsing large joint arthritis; neuropathy and meningoencephalitis are rare in children.
The selection, route, and duration of antibiotic therapy depend upon the child’s age, stage of Lyme disease, and site of infection. There is no convincing evidence for chronic Lyme disease, and courses of therapy longer than 4 weeks are not supported by the existing literature.
Rocky Mountain spotted fever (RMSF) is a rickettsial disease most common in the southeastern and south/central Midwest characterized by fever, headache, and rash. The rash begins as a maculopapular rash that then becomes petechial; it starts on the wrists/ankles and spreads centrally. Untreated RMSF can lead to multiorgan system failure and death. Children suspected of having RMSF should be treated empirically with doxycycline without waiting upon serologic confirmation.
Ehrlichiosis is divided into two forms: human monocytic ehrlichiosis (HME) and human granulocytic anaplasmosis (HMA). The two entities cause very similar symptomatology, of fever, rash, myalgias, and headache, although HME can cause more severe symptoms than HMA. They both are treated with doxycycline.
Tularemia can be spread by contact with ticks or rabbits and other small mammals. A number of syndromes may be seen in patients, including ocular, lymphatic, and pharyngeal involvement. The treatment of choice is an aminoglycoside.
Babesiosis causes a malaria-like illness in children; disease severity is highest in asplenic children. Diagnosis (peripheral smear) and treatment (clindamycin + quinine) are the same as for malaria.

Ticks can transmit a number of diseases to children; these include bacterial (Lyme, RMSF, ehrlichiosis, tularemia), protozoal (babesiosis), and viral (Colorado tick fever) pathogens. The index of suspicion for tick-borne pathogens should be high in children with unexplained fever or dermatologic findings: a child’s play or other activities may put them at higher risk of contact with ticks than adults; the history of tick exposure infrequently is elicited; even if a child notes a tick, tick removal may not occur promptly or thoroughly; and children may become more ill with certain tick-borne diseases than adults.

Tick season will vary geographically (Table 65-1), but most tick-borne illnesses occur from April to October.¹ Tick-borne diseases may be seen throughout the year in warmer regions or after a mild winter, as a hard freeze is needed to kill ticks. Ticks often need to be attached for up to 48 hours prior to transmission of disease. Thus, if a tick can be easily brushed off a child, it is unlikely to result in disease. Ticks tend to attach as in the larval or nymph forms, when they are very small, making detection challenging until the tick is engorged. Almost all disease-bearing ticks in the United States are hard ticks (rigid exoskeleton covering their dorsum). In male ticks, this covers the entire back, whereas it only covers the anterior aspect in females allowing the already larger-than-male female tick to engorge more dramatically after feeding.¹ Knowledge of the appearance of different tick species (Fig. 65-1)² can help narrow the differential diagnosis.

TABLE 65-1Distribution of Tick-Borne Disease in the United States

Disease	Vector	Vertebrate Reservoir of Disease	Distribution in the United States
Babesiosis (Babesia microti)	Ixodes tick	Rodents, cattle	New England, Mid-Atlantic states, upper Midwest in Great Lakes area
Colorado tick fever	Dermacentor tick	Rodents, porcupine	Colorado, Montana, Utah, Wyoming account for over 90% of cases
Human granulocytic anaplasmosis (Anaplasma phagocytophila)	Ixodes tick	Dogs, rodents	New England, upper Midwest in Great Lakes area, northern California
Human monocytic ehrlichiosis (Ehrlichia chaffeensis)	Dermacentor Amblyomma tick	Dogs	Southeast, south central, and Midwestern states
Lyme disease (Borrelia burgdorferi)	Ixodes tick	Deer, rodents, raccoon	New England, Mid-Atlantic states, upper Midwest in Great Lakes area; some cases seen along West Coast (Ixodes pacificus)
Q fever (Coxiella burnetii)	Dermacentor tick	Cattle, goats, sheep	Worldwide; over 50% of US cases are from 7 states: California, Colorado, Illinois, Kentucky, Missouri, Tennessee, Texas
Rocky Mountain spotted fever (Rickettsia rickettsii)	Dermacentor tick	None	Southeast, southern Midwest; over 50% of US cases from Oklahoma, Tennessee, Arkansas
Tularemia (Francisella tularensis)	Dermacentor, Amblyomma ticks	Rabbits (frozen rabbits may remain infectious for years), hares, prairie dogs, skunks, raccoons, rodents	Southern Midwest, Western states, but sporadic cases reported throughout continental US

FIGURE 65-1.

Relative tick sizes. (Reproduced with permission from Centers for Disease Control and Prevention. http://www.cdc.gov/ticks/life_cycle_and_hosts.html.)

Strategies for tick prevention include environmental control such as spraying around the perimeter of yards, pet grooming and use of topical agents to rapidly remove adhered ticks, long pants tucked into socks and long-sleeved shirts, and light-colored clothing to detect dark-bodied ticks. Chemical control includes spraying clothing with permethrin spray (generally lasting 5–10 machine washings), and skin with DEET. Permethrin is more effective than DEET. Children should be checked for ticks after playing outside in endemic areas, particularly checking the lower extremities and any site constricted by clothing (waist) or backpacks (axillae).

If ticks are encountered, viscous lidocaine may be applied to kill the tick and provide local anesthesia. Fine-tipped forceps are applied parallel to the skin as close to the skin as possible to grasp the head. The tick is pulled upward with even pressure. Twisting or jerking can result in mouthparts breaking off and remaining embedded in the skin. If mouthparts are retained, the area should be irrigated, but dissection to retrieve mouthparts is unnecessary.³ Parents should be encouraged to not apply heat or other irritants to ticks, as an irritated tick has a tendency to vomit and/or defecate, increasing the risk of disease transmission.

There are several common tick-borne diseases seen in the United States (see below), while others have very low prevalence, such as Colorado tick fever and Q fever⁴ (included in Tables 65-2 and 65-3). See Figure 65-2 for algorithm for differentiating tick-borne illnesses.

TABLE 65-2Incubation Period, Symptoms, and Diagnosis of Tick-Borne Illnesses

Disease	Incubation Period	Symptoms	Diagnosis
Babesiosis	1–4 wk	Fever, chills, myalgias, nausea, headache, nonproductive cough; may also have jaundice Illness much more severe in asplenic patients, other immunocompromised hosts, or chronic heart, hepatic, or lung disease	Thick and thin smears with Giemsa/Wright staining (can see trophozoites looking like a Maltese Cross) Anemia, low haptoglobin, elevated lactate dehydrogenase and reticulocyte count; thrombocytopenia is common
Colorado tick fever	3–7 d	Biphasic fever (for 3–4 d, then afebrile 1–3 d, then febrile again × 2–3 d), retro-orbital headache, photophobia, myalgia, nausea, vomiting Complications: meningoencephalitis, hemorrhagic fever	Serologies Ancillary: leukopenia, thrombocytopenia, elevated hepatic transaminases and creatine kinase
Human granulocytic anaplasmosis	5–10 d	Fever, chills, headache, malaise, myalgia; rash after 1 wk of illness Complications: ARDS, meningoencephalitis (lymphocytic CSF pleocytosis), DIC, renal failure	Serology (4-fold change in acute and convalescent titers) or PCR Cross-reactivity exists with ehrlichiosis Ancillary: leukopenia, thrombocytopenia, elevated hepatic transaminases
Human monocytic ehrlichiosis	5–10 d	Fever, chills, headache, malaise, myalgia; rash after 1 wk of illness Complications: ARDS, meningoencephalitis (lymphocytic CSF pleocytosis), DIC, renal failure Ehrlichiosis often causes more severe disease manifestations than anaplasmosis	Serology (4-fold change in acute and convalescent titers) or PCR Cross-reactivity exists with anaplasmosis Ancillary: leukopenia, thrombocytopenia, elevated hepatic transaminases
Lyme disease	3–30 d	Stage 1: EM at site of bite, fever, malaise, myalgias, arthralgias, regional adenopathy Stage 2: multiple EM, cranial nerve palsies, meningitis, headache, AV block, myocarditis, oligoarticular arthritis Stage 3: more chronic neurological (encephalopathy) and arthritic (refractory joint pain) symptoms	For stage 1 Lyme, diagnosis is clinical and better than serologic diagnosis (treatment in stage 1 can blunt antibody response) For latter stages, serology, PCR diagnosis for arthritis and meningitis or encephalitis
Q fever	2–3 wk	Fever, headache, malaise, myalgias, cough, chest pain, gastroenteritis Complications: pneumonia, hepatitis, myocarditis, meningoencephalitis Chronic Q fever occurs in 1% of acutely ill patients (higher risk in pregnant or immunocompromised patients), and manifestations may include endocarditis, hepatitis, and aneurysms	Serology (4-fold change in acute and convalescent titers) or PCR Culture usually is not attempted given risk to laboratory workers
Rocky Mountain spotted fever	2–14 d	“Classic” triad of fever, rash, and headache seen in a minority of children; also may see myalgia, vomiting, abdominal pain, photophobia Rash after 2–5 d of fever: initially blanching erythematous macules on wrists/ankles, then spreads centrally and becomes petechial	Serology takes up to 7–10 d to become positive Do not wait for confirmation to initiate therapy! Ancillary: anemia, thrombocytopenia, hyponatremia, elevated hepatic transaminases, increased bilirubin and creatine kinase
Tularemia	3–5 d	Abrupt onset of fever, chills, myalgia, headache. Several syndromes exist: ulceroglandular, glandular, oculoglandular, oropharyngeal, and vesicular skin lesions Complications: pneumonic tularemia	Serology (can cross-react with Brucella, Legionella) Alert laboratory if suspect tularemia, as it can pose a hazard to workers

TABLE 65-3Treatment of Other Tick-Borne Illness

Disease	First-line	Dose(s)^a	Alternative	Caveats
Babesiosis	Clindamycin + quinine × 7–10 d	Clindamycin 10 mg/kg every 8 hours [600 mg/dose] Quinine 10 mg/kg every 8 hours [650 mg/dose]	Atovaquone + azithromycin	Consider exchange transfusion for hemodynamically unstable patients and/or those with parasitemia of ≥10%
Colorado tick fever	Supportive care		–	Is usually a self-limited illness; approximately 10 cases seen per year in US
Human granulocytic anaplasmosis	Doxycycline × 7 d minimum or until afebrile × 3 d, whichever is longer	2.2 mg/kg every 12 hours [100 mg/dose]	–	Failure to respond within 72 h should suggest infection with another agent
Human monocytic ehrlichiosis	Doxycycline × 7 d minimum or until afebrile × 3 d, whichever is longer	2.2 mg/kg every 12 hours [100 mg/dose]	–	Failure to respond within 72 h should suggest infection with another agent
Q fever	Doxycycline × 10–14 d	2 mg/kg every 12 hours [100 mg/dose]	Fluoroquinolones, chloramphenicol	Generally is a self-limited illness; endocarditis requires long (up to 18 months) course of therapy
Rocky Mountain spotted fever	Doxycycline × 7–10 d or until afebrile for at least 3 d	2 mg/kg every 12 hours [100 mg/dose]	Chloramphenicol	Doxycycline is treatment of choice irrespective of age, also treats ehrlichiosis
Tularemia	Aminoglycoside × 10 d (longer courses for pneumonic tularemia or severe illness)	Gentamicin 2.5 mg/kg every 8 hours	Fluoroquinolones, doxycycline, chloramphenicol	Resistant to beta-lactams (penicillin, cephalosporins)