Tick-borne diseases

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Tick-borne diseases are predominantly caused by pathogens that are transmitted by ticks (and sometimes other vectors), except tick paralysis, which is caused by a neurotoxin produced by the tick itself. Tick-borne diseases are typically associated with specific geographical regions. The most clinically significant tick-borne diseases in the US include Lyme disease, Rocky Mountain spotted fever (RMSF), babesiosis, ehrlichiosis, anaplasmosis, tularemia, Colorado tick fever, tick-borne relapsing fever, southern tick‑associated rash illness, tick paralysis, and the more recently recognized alpha-gal syndrome. While manifestations of these conditions vary, common symptoms include fever, flu-like symptoms, and skin rashes. Most tick-borne diseases are treated with antibiotics and patients usually respond well to treatment.

Lyme disease is covered in more detail in its own article.

Background

• Epidemiology: ∼ 5500 cases were reported in 2018 ^[8]
• Pathogen: : Rickettsia rickettsii
• Vector
  • American dog tick (Dermacentor variabilis)
  • Rocky Mountain wood tick (Dermacentor andersoni)
  • Brown dog tick (Rhipicephalus sanguineus)
• Distribution
  • Cases reported across the contiguous US
  • Higher density especially in the midwestern, northeastern, and southern US
• Pathophysiology: Rickettsia species invade capillary endothelium → inflammation → small vessel vasculitis

Clinical features ^[9]

• Incubation period: 4–10 days
• Flu-like symptoms (e.g., fever, headache)
• Blanching maculopapular rash: begins on the wrists and ankles
  • Spreads to the trunk, palms, and soles
  • May become petechial and/or hemorrhagic
• Ankle and/or wrist swelling
• Gastrointestinal symptoms (e.g., nausea, vomiting, abdominal pain)
• Meningitis, focal neurological deficits
• Rapid clinical deterioration with shock and multiorgan dysfunction (e.g., DIC)

The rash may be less obvious in dark-skinned individuals; therefore, close inspection and a high degree of clinical suspicion are required. ^[10]

Diagnostics ^[10][11][12]

RMSF is a clinical diagnosis.

• Laboratory studies ^[11]
  • CBC: typically normal WBC count, thrombocytopenia
  • BMP: ↓ Na, ↓ renal function in severe cases
  • Mildly ↑ AST and/or ALT
  • ↑ PT, ↑ INR, ↑ PTT
• Other supportive studies: ECG , CXR ^[10]
• Confirmatory studies: should be performed in all patients ^[12]
  • Indirect fluorescent antibody (IFA) test (gold standard): four-fold increase in IgG-specific antibodies
  • PCR: detection of R. rickettsii DNA in a skin biopsy specimen or acute phase whole blood specimen
  • Immunohistochemical staining of R. rickettsii in a skin biopsy specimen
• Lumbar puncture: to rule out meningitis in patients with neurological features ^[11]
  • Pleocytosis with lymphocytic or monocytic predominance
  • ↑ Protein
  • Normal glucose

Do not delay treatment while waiting for confirmatory studies and do not discontinue treatment based solely on the results. ^[12]

RMSF is a nationally notifiable disease in the United States. Contact the state or local health department if a potential case is suspected. ^[10]

Differential diagnosis ^[12]

• Meningococcemia
• Lyme disease
• Endocarditis
• Hemorrhagic fever (e.g., Ebola fever, Hanta fever)
• Vasculitis

Treatment

Initiate empiric antibiotic treatment immediately and consider consulting local infectious disease specialists. ^[12]

• Doxycycline ^[12][13]
• Supportive care in severe disease: e.g., broad-spectrum antibiotics for febrile patients in septic shock
• Options during pregnancy ^[12][14]
  • Doxycycline ^[14]
  • Chloramphenicol during the first and second trimester ^[12]

Treatment should be initiated as soon as RMSF is suspected, as it can be fatal if not treated early.

Disposition ^[12]

• Consider hospitalization for patients who:
  • Require supportive care
  • Have altered mental status
  • Are unable to adhere to follow-up
• Escalate to critical care unit based on clinical condition.
• In selected cases, consider discharge with oral antibiotics.

Prognosis ^[15]

• If treated within the first 5 days, patients typically fully recover without hospitalization.
• If treated after the first 5 days, symptoms are more severe and often require hospitalization. There is also a greater risk of long-term consequences of ischemia (e.g., amputations, paralysis, hearing loss, intellectual disability).
• If not treated early enough, the disease can be fatal.

Background

• Epidemiology: > 2000 cases reported in the US annually ^[3]
• Pathogen: Babesia species (e.g., Babesia microti)
• Vector: deer tick (Ixodes scapularis)
  • Ixodes is also the vector for Borrelia burgdorferi and Anaplasma species.
  • Ticks are often coinfected; therefore, patients with babesiosis often also have Lyme disease. ^[3]
• Distribution
  • In the US, B. microti causes endemic disease in midwestern (especially Minnesota and Wisconsin) and northeastern states.
  • Other species of Babesia cause disease sporadically throughout the world. ^[16]
• Transmission ^[3]
  • Tick bite (most common)
  • Exposure to infected blood, i.e, transfusions, organ transplantation, perinatal
• Incubation period: 1–4 weeks after a tick bite or 1–9 weeks after contaminated blood transfusion ^[17][18]
• Risk factors for severe babesiosis ^[3]
  • Asplenia
  • Malignancy
  • Heart failure
  • HIV infection
  • Use of immunosuppressive drugs
  • Age > 50 years or < 28 days ^[17]

Clinical features ^[3][17]

Babesiosis has no disease-specific distinguishing clinical features.

• Fever and other flu-like symptoms
• Anorexia
• Nonproductive cough
• Dark urine, jaundice from hemolytic anemia
• Mild splenomegaly and/or hepatomegaly
• Gastrointestinal symptoms (e.g., nausea, vomiting, abdominal pain)
• Typically no rash; may have petechiae, ecchymoses

Diagnostics ^[3][17]

• Supportive laboratory findings
  • CBC: ↓ hematocrit, thrombocytopenia, ↑ reticulocyte count
  • ↑ BUN, ↑ creatinine; proteinuria ^[18]
  • Hemolysis: ↓ serum haptoglobin, ↑ LDH, ↑ total and indirect bilirubin
  • Elevated transaminases
• Diagnostic confirmation
  • Indication: characteristic clinical features, supportive laboratory findings, and relevant exposure history ^[3]
  • Modalities
    • Peripheral blood smear showing Babesia as intraerythrocytic rings and/or Maltese cross
    • Detection of Babesia DNA on a blood sample (e.g., PCR)

Differential diagnoses

• Malaria
• Lyme disease
• Ehrlichiosis

Treatment ^[3]

Consult an infectious disease specialist for guidance.

• Antibiotic regimens for immunocompetent patients
  • Mild to moderate disease; (ambulatory patients): oral atovaquone (off-label) PLUS oral azithromycin (off-label) ^[3]
  • Severe disease; (hospitalized patients): oral atovaquone (off-label) PLUS IV azithromycin (off-label) ^[3]
  • Alternative regimen: quinine PLUS clindamycin
• Exchange transfusion: consider for patients with parasitemia > 10% and/or severe disease ^[3]

Patients who are immunocompromised may require a higher dose of azithromycin (e.g., 500–1000 mg daily) and longer treatment duration (e.g., ≥ 6 weeks). ^[3]

Complications ^[3]

• Warm autoimmune hemolytic anemia
• DIC
• Shock
• ARDS
• Acute kidney injury
• Heart failure
• Acute liver failure
• Splenic infarct; splenic rupture

• Pathogens
  • Ehrlichia chaffeensis
  • Ehrlichia ewingii
  • Ehrlichia muris eauclairensis
• Vectors
  • Lone star tick (Amblyomma americanum): E. chaffeensis and E. ewingii
  • Deer tick (Ixodes scapularis): E. muris eauclairensis
• Distribution
  • Mainly east of the Rocky Mountains
  • Also some cases in the Southwest
• Clinical features
  • Incubation period: 1–2 weeks ^[19]
  • Flu-like symptoms (e.g., fever, myalgia)
  • Gastrointestinal symptoms (e.g., nausea, vomiting, abdominal pain)
  • Hepatomegaly
  • Rarely, symptoms of meningitis and/or encephalitis (e.g., headache, altered mental status, stiff neck, neurological deficits)
  • Sometimes an erythematous maculopapular or petechial rash ^[20]
    • Adults: ∼ 30% of cases
    • Children: ∼ 60% of cases
• Diagnostics ^[12]
  • Ehrlichiosis is a clinical diagnosis.
  • Laboratory studies
    • CBC: anemia, thrombocytopenia, leukopenia
    • Mild to moderate ↑ AST and/or ALT
    • BMP: mild to moderate ↓ Na
  • Peripheral blood smear (with Wright stain or Giemsa stain): leukocytes with morulae (clustered inclusion bodies that resemble a mulberry) ; ^[12][21]
    • E. chaffeensis infection: morulae within monocytes
    • E. ewingii infection: morulae within granulocytes
  • Confirmatory tests: should be performed in all patients
    • IFA test (gold standard): four-fold increase in IgG-specific antibodies
    • PCR: detection of Ehrlichia DNA in a whole blood sample
• Differential diagnosis: RMSF
• Treatment: : doxycycline ^[12][13]
• Disposition: In selected cases, consider discharge with oral antibiotics. ^[12]

Ehrlichiosis is a nationally notifiable disease in the United States. Contact the state or local health department if a potential case is suspected. ^[10]

• Pathogen: Anaplasma phagocytophilum
• Vector
  • Deer tick (Ixodes scapularis)
  • Western black-legged tick (Ixodes pacificus)
  • Ixodes is also the vector for Borrelia burgdorferi and Babesia species, so coinfection is possible.
• Reservoir: deer and mice
• Distribution
  • Upper midwestern and northeastern US
  • Growing number of cases on the West Coast
• Clinical features
  • Incubation period: 1–2 weeks ^[22]
  • Fever and other flu-like symptoms (headache, chills, muscle aches)
  • Gastrointestinal symptoms (e.g., nausea, vomiting, abdominal pain)
  • Cough
  • Typically no rash
• Diagnostics ^[12]
  • Anaplasmosis is a clinical diagnosis.
  • Laboratory studies
    • CBC: mild anemia, thrombocytopenia, leukopenia
    • Mild to moderate ↑ AST and/or ALT
  • Peripheral blood smear may show morulae within granulocytes.
  • Confirmatory tests: should be performed in all patients
    • IFA test (gold standard): four-fold increase in IgG-specific antibodies
    • PCR: detection of Anaplasma DNA in a whole blood sample
• Treatment: : doxycycline ^[12]
• Disposition: In selected cases, consider discharge with oral antibiotics. ^[12]

Anaplasmosis is a nationally notifiable disease in the United States. Contact the state or local health department if a potential case is suspected. ^[10]

Tularemia is a nationally notifiable disease in the United States. Contact the state or local health department if a potential case is suspected. ^[4]

Background ^[4]

• Epidemiology: ∼ 250 cases/year in the US ^[4]
• Pathogen: Francisella tularensis (facultative intracellular bacterium)
• Distribution
  • F. tularensis tularensis is a highly virulent subspecies that is be found in all US states except Hawaii.
  • Less virulent species (e.g., F. tularensis holarctica) have a wider distribution in the northern hemisphere. ^[23]
• Reservoir: rabbits, hares, and rodents (e.g., voles, muskrats)
• Vectors
  • Ticks (Amblyomma americanum, Dermacentor spp.)
  • Deer flies (Chrysops species)
• Transmission
  • Bite from a vector (most common)
  • Direct contact with the pathogen, e.g.:
    • Inhalation of contaminated dust or aerosols (may result in pulmonary disease)
    • Ingestion of contaminated food or water
    • Skin contact with infected animals
    • Exposure of laboratory personnel to diagnostic cultures ^[23]
• Incubation period: typically 3–5 days (range 1–21 days) ^[4]

Tularemia is highly contagious and easily disseminated; it is considered a pathogen of the highest concern as a possible bioweapon. ^[24]

Clinical features ^[4]

• General symptoms
  • Flu-like symptoms
  • High fever
  • Anorexia
  • Cough
  • Sore throat
  • Abdominal pain, vomiting, diarrhea
• Specific manifestations
  • Ulceroglandular tularemia (most common form): tender localized lymphadenopathy, skin ulcer at the entry site of F. tularensis
  • Glandular tularemia: tender regional lymphadenopathy with no skin ulcer
  • Oculoglandular tularemia: conjunctivitis, pain, excessive lacrimation, photophobia, tender preauricular and/or cervical lymphadenopathy
  • Oropharyngeal tularemia: severe sore throat, mouth ulcers, exudative tonsillitis or pharyngitis, tender cervical, preparotid, or retropharyngeal lymphadenopathy
  • Pneumonic tularemia (most severe form): cough, pleuritic chest pain, chest tightness, dyspnea, hilar adenopathy, infiltrate, or pleural effusion may be present
  • Typhoidal tularemia: fever, nonlocalizing features

Diagnostics ^[4]

Consult an infectious diseases specialist for guidance on appropriate diagnostic testing and specimen handling.

• Diagnostic confirmation
  • Positive culture (e.g., on charcoal yeast extract agar) from a tissue sample
  • Conversion to positive IgM and/or IgG antibodies in paired acute and convalescent serum samples ^[4]
• Supportive laboratory findings ^[23]
  • CBC: Normal or ↑ leukocyte count, thrombocytopenia
  • Elevated transaminases
• Chest imaging (e.g., CXR, CT): Findings in pneumonic tularemia are consistent with features of pneumonia, e.g., pulmonary infiltrates, hilar lymphadenopathy, and/or pleural effusion. ^[24]

F. tularensis antibodies may be undetectable until 2–3 weeks after symptom onset and may remain detectable for years after recovery. ^[4]

Differential diagnoses

• Cat scratch disease
• Brucellosis
• Community-acquired pneumonia

Treatment ^[4]

Consult an infectious disease specialist.

• Antibiotic regimens
  • Gentamicin (off-label) is preferred for severe tularemia. ^[4]
  • Ciprofloxacin (off-label) ^[4]
  • Doxycycline ^[4]
  • Streptomycin
• Isolation: standard precautions

• Pathogen: Colorado tick fever virus (CTFV), an RNA virus
• Vector: Rocky Mountain wood tick (Dermacentor andersoni)
• Distribution: western US
• Clinical features
  • Incubation period: 1–14 days ^[25]
  • Flu-like symptoms: often biphasic (fever remits after 2–4 days and returns 1–3 days later) ^[26]
  • Possibly conjunctival injection, pharyngeal erythema, and cervical lymphadenopathy
  • Petechial or maculopapular rash
• Diagnostics
  • CBC: leukopenia, thrombocytopenia
  • Peripheral blood smear may show atypical lymphocytes.
  • Confirmatory test
    • < 2 weeks after onset of symptoms onset: viral RNA detection by RT-PCR of blood sample
    • > 2 weeks after onset of symptoms: serum assay to detect CTFV-specific IgM antibodies ^[26]
• Treatment: only supportive management

• Pathogen: Borrelia hermsii
• Vector: Vector: Ornithodoros soft ticks (including O. hermsi, O. parkeri, O. turicata)
• Distribution: western US and Texas
• Clinical features
  • Incubation period: 4–18 days ^[27]
  • Recurring episodes of high fever for 3 days and an afebrile period of 7 days ^[6]
  • Arthralgia (∼ 70%)
  • Gastrointestinal symptoms (e.g., nausea, vomiting, abdominal pain, diarrhea)
  • Less commonly
    • Hepatic manifestations (e.g., jaundice, hepatosplenomegaly)
    • Symptoms of meningitis (e.g., confusion, photophobia, neck pain, nuchal rigidity)
  • Macular rash or scattered petechiae may occur.
• Diagnostics
  • CBC: normal or ↑ leukocyte count, thrombocytopenia
  • Mild ↑ in serum bilirubin level
  • Slightly prolonged PT and aPTT
  • ↑ ESR
  • Confirmatory test
    • Direct observation of spirochetes in peripheral blood smears, bone marrow, or CSF with Giemsa-Wright stain, acridine orange stain, or dark-field microscopy
    • OR IFA test: four-fold increase in Borrelia-specific antibody titers between acute and convalescent serum samples
• Treatment
  • No CNS involvement:
    • First line: tetracycline
    • Second line: erythromycin
  • CNS involvement: ceftriaxone

• Pathogen: unknown
• Vector: Lone star tick (Amblyomma americanum)
• Distribution: southeastern and eastern US
• Clinical features
  • Incubation period: ∼ 7 days ^[28]
  • Resembles early localized Lyme disease with erythema migrans-like lesion and possibly flu-like symptoms ^[28]
  • Not associated with clinical features of early disseminated (e.g., arthralgia, facial nerve palsy, cardiac complications) or late Lyme disease (e.g., progressive encephalomyelitis).
• Diagnostics: Clinically determined by ruling out Lyme disease.
• Treatment: doxycycline, amoxicillin, OR cefuroxime axetil (See “Treatment of Lyme disease” for details.) ^[29]

• Definition: a rare syndrome caused by the salivary neurotoxin of certain ticks, characterized by acute ataxia, that progresses to ascending paralysis
• Epidemiology: most commonly occurs in children and women
• Etiology: > 40 tick species are associated with tick paralysis
  • Most common in the US: Dermacentor species (e.g., Rocky Mountain wood tick)
  • Others: Lone star tick (Amblyomma americanum), deer tick (Ixodes scapularis)
• Distribution: most commonly in the Rocky Mountains and northwestern US
• Pathophysiology
  • Paralysis is caused by tick neurotoxin, which is produced in the tick's salivary gland and introduced into the person's blood.
  • Possible mechanisms:
    • Dermacentor species: inhibition of sodium flux across axonal membranes
    • Ixodes species: inhibition of acetylcholine release at the neuromuscular junction
  • Tick neurotoxin → impairment of motor nerve transmission → muscle weakness → paralysis
• Clinical features
  • Symptoms begin within 2–7 days of the initial tick bite.
  • Typically starts with weakness in the lower extremities
  • Escalates to ascending flaccid paralysis that progresses rapidly and can lead to respiratory failure due to respiratory muscle weakness
  • Sensory deficits are usually absent.
  • Cranial nerve palsies may occur (e.g., CN III palsy).
  • No fever or rash
• Diagnostics
  • Clinically determined by finding a tick attached to the body and/or ruling out other tick-borne diseases associated with neurological deficits (e.g., Lyme disease, Q fever).
  • CSF examination is usually normal in tick-borne paralysis.
• Differential diagnosis
  • Guillain-Barré syndrome
  • Botulism
  • Poliomyelitis
  • Myasthenia gravis
  • Spinal cord lesion
• Treatment
  • Locate and remove the tick.
  • Supportive therapy (e.g., ventilatory support for patients with respiratory failure)

References: ^[30]

• Definition: an allergic reaction to the oligosaccharide galactose-alpha-1,3-galactose (alpha-gal) found on the cells of nonprimate mammals (e.g., cows, pigs, lambs) that is thought to occur after a parasitic infection or the bite of a tick ^[7]
• Etiology ^[7]
  • Lone star tick (Amblyomma americanum)
  • Parasitic infections (e.g., ascariasis) have also been implicated.
• Reservoir: deer (principal host)
• Distribution ^[7]
  • US: Midwest, southeastern and eastern US
  • Worldwide: Western Europe, South Africa, Japan, Australia
• Pathophysiology
  • Sensitization: Lone star tick bite or parasitic infection → production of IgE antibodies against alpha-gal
  • Type I hypersensitivity: consumption of mammalian-derived products in a sensitized individual → alpha-gal absorbed in GI tract enters the circulation → IgE against alpha-gal → mast-cell degranulation
• Clinical features ^[7]
  • Typically present 2–6 hours after ingestion
  • May be asymptomatic ^[7]
  • GI features
    • Abdominal pain (most common)
    • Vomiting
    • Diarrhea
  • Mucocutaneous features: urticaria, angioedema
  • Anaphylaxis (most severe presentation)
• Diagnosis: primarily a clinical diagnosis, but may be supported by the following ^[7]
  • Positive clinical response after ≥ 1 month of alpha-gal avoidance
  • Serum: ↑ IgE against alpha-gal titers
• Management: should be specialist-guided (e.g., gastroenterology, immunology) ^[7]
  • Alpha-gal avoidance
    • Diet: Avoid mammalian-derived meats and products.
    • Medical products: e.g., cetuximab, pancreatic enzymes ^[7]
  • Pharmacotherapy: Consider immediately after exposure.
    • Oral antihistamines (e.g., diphenhydramine ) ^[7]
    • AND/OR epinephrine autoinjector
  • Referral: Consider consulting immunology and/or allergy specialists for patients with cutaneous or systemic symptoms (e.g., hypotension, urticaria).
• Prognosis: Sensitization to alpha-gal may fade or resolve over time. ^[7]
• Prevention: tick bite prevention (further tick bites may worsen the allergy)

Alpha-gal does not cause anemia, GI bleeding, or weight loss. If these features are present consider alternative diagnoses. ^[7]

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