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Tick-borne Disease: Laboratory Support of Diagnosis and Management

Tick-borne Disease: Laboratory Support of Diagnosis and Management

Clinical Focus

Tick-borne Disease

Laboratory Support of Diagnosis and Management

  

Contents:

Clinical Background - Table 1  - Table 2  - Table 3  - Figure

Individuals Suitable for Testing

Test Availability - Table 4

Test Selection and Interpretation - Table 5 - Table 6 - Table 7

References
 

Clinical Background [return to contents]

Tick-borne diseases are caused by infections transmitted to humans via a tick vector such as the deer tick, dog tick, wood tick, and Lone Star tick. In the United States, transmission occurs primarily in the spring and summer months. Causative agents include bacteria (including rickettsia), viruses, and protozoa. The incidence varies by geographic location and causative agent (Table 1). Clinical manifestations also vary depending on the disorder, but frequently include fever, chills, sweating, headaches, myalgia, arthralgia, nausea, and vomiting. A rash or lesion at the site of the bite may or may not be present. More severe disease may result in hematologic, respiratory, cardiac, and neurologic complications as well as kidney or liver failure and arthritis. Although approximately 2% to 5% of the cases end in death, antimicrobial agents such as doxycycline and amoxicillin are usually effective.2 Coinfection with more than 1 causative agent (eg, Borrelia burgdorferi and Babesia microti) may complicate the diagnosis and can affect antimicrobial selection.4

Table 1. Incidence of Tick-borne Diseases
Disorder

Causative Organism

Vector Tick

Reported Cases,

US, 20101

US Geographic Distribution (in Order of Decreasing Incidence)1

Lyme disease Borrelia
burgdorferi

• Black-legged tick

(Ixodes pacificus)

• Deer tick (Ixodes

scapularis)

30,158
(22,561
confirmed)
 

• Mid-Atlantic

(upstate NY, PA, NJ)

• New England (CT,

MA, NH)

• South Atlantic (MD,

VA, DE)

• West North Central

(MN)

Ehrlichiosis

 

 

 

 

Human granulocyte anaplasmosis (HGA)a

Anaplasma phagocytophilum

• Black-legged tick

(Ixodes pacificus)

• Deer tick (Ixodes

scapularis)

1,761

• Mid-Atlantic

(upstate NY)

• West North Central

(MN)

Human
monocyte (HME)

Ehrlichia chaffeensis

• Lone Star tick

(Amblyomma

americanum)

• Dog tick

(Dermacentor

variabilis)

749

• Mid-Atlantic

(upstate NY)

• South Atlantic (NC)

• West North Central

(MO)

• West South Central

(OK)

Human E ewingii and other

E ewingii and unknown

• Lone Star tick 
  (Amblyomma  
  americanum
) and
  unknown

114

• East North Central

(WI)

• South Atlantic (MD)

Colorado tick fever (CTF)

Coltivirus species

• Wood tick

(Dermacentor

andersoni)

200–300/yr2

• Western US

Q fever

Coxiella burnetii

• Wood tick

(Dermacentor

andersoni)

131 (106 acute,
25 chronic)

• Mountain (CO)

• East North Central

(IL)

• Pacific (CA)

• West North Central

• South Atlantic

Tularemia

Francisella tularensis

• Lone Star tick

(Amblyomma

americanum)

• Wood tick

(Dermacentor

andersoni)

• Dog tick

(Dermacentor

variabilis)

124

• West North Central

(MO)

• Mountain (NM)

Tick-borne relapsing fever (TBRF)

Borrelia hermsii

Ornithodoros

species

35/yr3

• West, South, and

Southwest US

Powassan encephalitis

Flavivirus species

Ixodes cookei

0

• Wisconsin

Babesiosis

Babesia microti

• Black-legged tick

(Ixodes pacificus)

• Deer tick (Ixodes

scapularis)

1,124b

• Northeastern

coast, MN, WI

Tick paralysis

Tick neurotoxin

• Lone Star tick

(Amblyomma

americanum)

Dermacentor

species

Unknown

• Western US;

Rocky Mountains

a Formerly known as human granulocytic ehrlichiosis (HGE).
b Includes confirmed and probable cases reported from 15 of 18 states where babesiosis is reportable.5

Diagnosis is primarily based on a history of exposure to an area where ticks are endemic and on clinical presentation; in symptomatic patients, a rash or lesion may provide the first clue to the diagnosis (Figure). Characteristics and clinical features of each tick-borne disease, in order of incidence, follow.

Figure. One Approach to the Differential Diagnosis of Tick-borne Diseases

Lyme Disease

Lyme disease, caused by Borrelia burgdorferi, is by far the most common tick-borne disease (Table 1). Clinical presentation can either be localized or disseminated. Characteristic of early localized disease is the presence of erythema migrans, a round or oval erythematous skin lesion with a bullseye pattern that develops at the site of the tick bite; it is usually present 7 to 14 days after the tick bite and should be 5 cm in largest diameter for a firm Lyme disease diagnosis.4 Disseminated disease that may affect the musculoskeletal, cardiac, or nervous system can follow erythema migrans within days or weeks and is considered early-stage disseminated disease. Lyme carditis may overlap temporally with neurologic Lyme disease (late-stage disseminated disease).

Tick-borne Rickettsial Diseases (TBRDs)

TBRDs include Rocky Mountain spotted fever (RMSF), human granulocytic anaplasmosis (HGA) (formerly known as human granulocytic ehrlichiosis), human monocytic ehrlichiosis (HME), and Ehrlichia ewingii infection.

RMSF has been reported from each of the 48 contiguous states, except Vermont and Maine. The causative organism, Rickettsia rickettsii, infects endothelial cells and causes a small-vessel vasculitis that usually results in a maculopapular or petechial rash. Vasculitis in organs such as the brain or lungs can lead to life-threatening complications.

Reported cases of E ewingii infection have primarily included immunocompromised patients from Missouri, Oklahoma, and Tennessee.7 HME, caused by E chaffeensis, is mostly identified in South-central, Southeastern, and Mid-Atlantic states, whereas HGA cases due to infection with A phagocytophilum are usually found in the Northeastern and upper Midwestern states.

TBRDs commonly manifest with an acute onset of nonspecific symptoms that mimic benign viral infections, making diagnosis difficult (Table 2). The presence or absence of a rash can be a useful diagnostic aid. Because antibiotic treatment is most effective when given early, therapy for symptomatic patients with clinically suspected TBRDs should not be delayed pending confirmatory laboratory results.7 Once the presumptive diagnosis of TBRD is made based on endemic exposure and clinical signs and symptoms, doxycycline is generally the drug of choice for both children and adults.7

Table 2. Clinical Features of Tick-borne Rickettsial Diseases7

Disease Incubation Period (Days) Signs and Symptoms Rash
Rocky Mountain spotted fever 2–14 Fever, headache, malaise, myalgia, nausea/vomiting Maculopapular rash 2–4 days after fever onset in 50%–80% of adults and >90% of children; frequently on palms and soles
Human monocytic ehrlichiosis 5–14 Fever, severe headache, malaise, myalgia Erythematous, maculopapular, or petechial rash in <30% of adults and ~60% of children
Human granulocytic anaplasmosis 5–21 Fever, headache, malaise, myalgia, vomiting Rare
Ehrlichia ewingii infection 5–14 Fever, headache, myalgia, nausea/vomiting Rare

Tick-borne Non-Rickettsial Diseases

Colorado Tick Fever
Colorado tick fever, which is caused by an arbovirus infection of erythrocytes, is found throughout the Rocky Mountain region of the United States. After a mean incubation time of 3 to 5 days, disease onset is abrupt; presenting symptoms include intense headache, severe myalgia, arthralgia, and a characteristic biphasic pattern of fever termed “saddleback” fever (Table 3). The fever lasts for 2 to 3 days, disappears, and then recurs for another 2 to 3 days. Rarely, severe complications such as central nervous system involvement and hemorrhage may occur, especially in children.

Table 3. Clinical Features of Tick-borne Non-Rickettsial Diseases5,6,8-10

Disease Incubation Period (Days) Common Signs and Symptoms
Colorado tick fever 3–10 Severe headache, severe myalgia, arthralgia, saddleback fever
Q fever 14–21 Prolonged fever, fatigue, sweating, chills, myalgia, headache, arthralgia, pneumonia, hepatitis
Tularemia 2–14 Fever, chills, headache, myalgia, arthralgia, papule/ulceration
Tick-borne relapsing fever 4– >18 Headache, myalgia, chills, nausea/vomiting, arthralgia
Babesiosis 7–42 Fever, chills, myalgia, hemolytic anemia

Q Fever
C burnetii (the bacterium responsible for Q fever) has been isolated from many species of ticks, but animals (eg, goats, cows, dog, cats, pigeons, sheep) serve as the major reservoir for human infection. The most common route of infection is inhalation of aerosolized bacteria from animal fluids such as urine, feces, and birth fluids.6 Q fever is asymptomatic in up to 60% of patients, but can manifest as acute and chronic disease.6,11 Acute Q fever tends to present with non-specific febrile symptoms (Table 3), frequently accompanied by pneumonia and hepatitis6; the triad of fever, hepatitis, and atypical pneumonia should increase suspicion for acute Q fever.11 Children with Q fever have less frequent and generally milder symptoms than adults, but are more likely to develop a rash. Because Q fever is associated with increased risk for adverse pregnancy outcomes, women of childbearing age with Q fever should be offered pregnancy testing.6 Patients with acute Q fever usually have normal leukocyte counts but may display a number of laboratory abnormalities, including thrombocytopenia and increased liver enzyme levels.

Treatment for acute Q fever should be started promptly, based on clinical evidence, and not delayed while awaiting laboratory results.6 Doxycycline is the treatment of choice for non-pregnant individuals age 8 and above.6

Chronic Q fever, which develops in <5% of patients, presents with organ involvement. Endocarditis is the most common clinical presentation (up to 70% of cases), followed by vascular infection. Patients with chronic Q fever typically have predisposing conditions such as heart valve lesions, immunodeficiencies, or vascular abnormalities. Combination therapy (doxycylcine plus hydroxychloroquine) is recommended for those with chronic infection.6

Some patients with acute Q fever develop post-Q fever fatigue syndrome, a distinct condition characterized by prolonged debilitating fatigue that may be accompanied by nonspecific symptoms (eg, nausea, headache, night sweats).6 Unlike chronic Q fever, post-Q fever fatigue syndrome usually affects patients with no known predisposing conditions other than symptomatic acute Q fever. Diagnosis is based on persistent (>1 year) fatigue and elevated antibody titers, after careful exclusion of chronic Q fever and other causes of fatigue. Treatment is not well defined but may include approaches similar those used for chronic fatigue syndrome.6

Tularemia
Tularemia, found most often in Missouri, Arkansas, and Oklahoma, is characterized by an ulcerative lesion at the site of the tick bite and by lymphadenopathy. An erythematous, tender, or puritic papule typically appears within 2 to 5 days and subsequently enlarges to form an ulcer with a black base. Additional symptoms of Francisella tularensis infection appear abruptly and include fever, chills, headache, and generalized myalgia and arthralgia (Table 3). Clinical consequences depend on the portal of entry and the extent of systemic involvement. Ulceroglandular and glandular forms account for 75% to 85% of cases; pneumonic tularemia, a pulmonary form that may be contracted by inhalation or hematogenous spread, accounts for about 18% of adult cases.12 Less common forms include oropharyngeal and oculoglandular disease. Diagnosis is made presumptively based on a history of exposure to a tick-endemic region and clinical signs and symptoms. Gentamicin or another aminoglycoside is suggested for treatment.12

Tick-borne Relapsing Fever (TBRF)
TBRF is caused by Borrelia hermsii and occurs west of the Mississippi River, especially in forested mountainous areas of the far Western states. TBRF is characterized by recurrent acute episodes of spirochetemia and fever. Following a mean incubation period of 7 days, the onset of illness is sudden, with headache, myalgia, chills, nausea/vomiting, and arthralgias that may be severe (Table 3). Fever is typically 104 °F and may be accompanied by delirium. Leukocytosis and thrombocytopenia are common, and splenomegaly may be present.

Symptoms intensify without treatment, and thus, treatment should be administered when clinical suspicion is high.3 Treatment recommendations for adults and children under 8 years of age may be found in reference 3.

Babesiosis
Babesiosis is caused by a protozoan infection (Babesia microti) of erythrocytes and shares clinical features with malaria. Babesiosis is now reportable in 18 states but is most common in New England, New York, New Jersey, Minnesota, and Wisconsin, which account for 97% of cases.5 Infection is primarily transmitted by ticks, although it can also be transmitted congenitally or through transfusion; 10 transfusion-associated cases were reported in 2011.5 The disease may be asymptomatic, or symptoms may appear 1 to 6 weeks after the tick bite. Symptoms vary widely but may include a gradual onset of irregular fever, chills, sweating, myalgia, arthralgia, nausea/vomiting, and fatigue (Table 3). Mild hepatosplenomegaly and mild hemolytic anemia may develop.

Individuals Suitable for Testing [return to contents]

  • Symptomatic individuals with a history of exposure to a tick-endemic area

Test Availability [return to contents]

Laboratory tests that can help confirm the clinical diagnosis include tick identification, microscopic visualization of the causative organism in blood or other clinical specimens, various serologic techniques, culture, and polymerase chain reaction (PCR)-based assays (Table 4).

Table 4. Tests Available for Diagnosis and Management of Tick-borne Diseases
Test Code Assay

Method

Clinical Use
All Tick-borne Diseases

3946(X)

Tick (and other Arthopods) Identification

Microscopy

Identify tick to determine risk of tick-borne disease; assist with differential diagnosis
Test Code Assay

Method

Clinical Use

Lyme Disease

34194

Lyme Disease Antibody Index for CNS Infection

Includes B burgdorferi IgG and IgM, total IgG and IgM, and albumin (all in CSF and serum) as well as B burgdorferi antibody index and albumin ratio.

ELISA;
nephelometry

Diagnose neurologic Lyme disease

29477(X)

Lyme Disease Antibody (IgG), Western Blot

Western blot

Diagnose Lyme disease in patients with equivocal or positive serology

8593

Lyme Disease Antibodies (IgG, IgM), Western Blot

6646

Lyme Disease Antibody with Reflex to Blot (IgG, IgM)a

EIA

Diagnose Lyme disease

15777
 

Lyme Disease (Borrelia spp) DNA, Qualitative Real-Time PCR, Bloodb,c

PCR

15564
 

Lyme Disease (Borrelia spp) DNA, Qualitative Real-Time PCR, Synovial Fluid/CSFb,c

PCR

Diagnose neurologic Lyme disease or Lyme arthritis

15510
 

Lyme Disease (Borrelia spp) DNA, Qualitative, Real-Time PCR, Tickb,c

PCR

Detect B burgdorferi in tick to assess risk of Lyme disease

15868
 

Lyme Disease (Borrelia spp) DNA, Qualitative Real-Time PCR, Urine b,c

PCR

Diagnose Lyme disease

90558

Tick ID with Reflex to Lyme Disease DNA, Real-Time PCR, Ticka,c

Microscopy; reflex to PCR

Identify tick and B burgdorferi to assess risk of tick-borne disease and assist with differential diagnosis
Test Code Assay

Method

Clinical Use

Rocky Mountain Spotted Fever

70191

Rickettsia rickettsii DNA, Real-Time PCRb,d,e

PCR

Diagnose RMSF

6419

Rickettsia (RMSF) Antibodies (IgG, IgM) with Reflex to Titersa

IFA

37507

Rickettsia Antibody Panel with Reflex
to Titersa

Includes IgG and IgM to causative organisms of RMSF and typhus fever.

IFA

Differential diagnosis of rickettsial disease

37478

Rickettsial Disease Panela

Includes IgG and IgM to causative organisms of RMSF, typhus fever, and Q-fever (phase I and II), with reflex to appropriate titers.

IFA

Test Code Assay

Method

Clinical Use

Ehrlichiosis

34464(X)

Anaplasma phagocytophilum Antibodies (IgG, IgM)d

IFA

Diagnose HGA

17320

Anaplasma phagocytophilum DNA, Qualitative, Real-Time PCRc,d

PCR

10611(X)

Anaplasma phagocytophilum and Ehrlichia chaffeensis Antibody Panelb

Includes IgG and IgM for both organisms.

IFA

Differential diagnosis of ehrlichiosis

34271(X)

Ehrlichia chaffeensis Antibodies (IgG, IgM)b

IFA

Diagnose HME

11353

Ehrlichia chaffeensis DNA, Real-Time PCRc,d

PCR

70194

Ehrlichia ewingii DNA, Real-Time PCRc,d,e

PCR

Diagnose E ewingii infection
 
Test Code Assay

Method

Clinical Use

Colorado Tick Fever

34986(X)

Colorado Tick Fever Antibody, IFAd

Includes IgG and IgM.

IFA

Diagnose Colorado tick fever
Test Code Assay

Method

Clinical Use

Q Fever

16596(X)

Coxiella burnetii DNA, Qualitative Real-Time PCRc,d

PCR

Diagnose acute and chronic Q fever

37071

Q Fever (Coxiella burnetii) Antibodies (IgG, IgM) with Reflex to Titersa

Includes antibodies for phase I and II disease.

IFA

Diagnose Q fever; distinguish acute from chronic disease; monitor therapy; detect relapse

37478

Rickettsial Disease Panela

Includes IgG and IgM to causative organisms of RMSF, typhus fever, and Q-fever (phase I and II), with reflex to appropriate titers.

IFA

Differential diagnosis of rickettsial disease
Test Code Assay

Method

Clinical Use

Tularemia

35176

Francisella tularensis Antibody, DA

Direct Agglutination
 

Diagnose tularemia
Test Code Assay

Method

Clinical Use

Tick-borne Relapsing Fever

34690(X)

Borrelia hermsii Antibody Panel, IFAb

Includes IgG and IgM.
 

IFA

Diagnose TBRF
Test Code Assay

Method

Clinical Use

Babesiosis

34300

Babesia microti Antibodies
(IgG, IgM)d

IFA

Diagnose babesiosis

37314(X)

Babesia microti DNA, Real-Time PCRc,d

PCR

831

Malaria/Babesia/Other Blood Parasites

Microscopy

EIA, ELISA, enzyme immunoassays; PCR, polymerase chain reaction; IFA, immunofluorescence assay; HGA, human granulocyte anaplasmosis, formerly known as human granulocytic ehrlichiosis (HGE); HME, human monocyte ehrlichiosis; TBRF, tick-borne relapsing fever.
a Reflex tests are performed at an additional charge and are associated with an additional CPT code(s).
b This test was developed and its performance characteristics have been determined by Focus Diagnostics. It has not been cleared or approved by the U.S. Food and Drug Administration. The FDA has determined that such clearance or approval is not necessary. Performance characteristics refer to the analytical performance of the test.
c Polymerase chain reaction (PCR) is performed pursuant to a license agreement with Roche Molecular Systems, Inc.
d This test was developed and its performance characteristics have been determined by Focus Diagnostics. Performance characteristics refer to the analytical performance of the test.

e Available from Focus Diagnostics.

Test Selection and Interpretation [return to contents]

Presence or absence of clinical symptoms, including the type of rash or lesion when present, guides the initial differential diagnosis of patients exposed to a tick-endemic area (Figure). This, in turn, guides appropriate test selection, presumably leading to confirmation of the suspected disorder.

The tables in this section, and the figure, are provided for informational purposes only and are not intended as medical advice. A physician’s test selection and interpretation, diagnosis, and patient management decisions should be based on his/her education, clinical expertise, and assessment of the patient.

Lyme Disease
Test Selection for Early Lyme Disease
Diagnosis of Lyme disease (B burgdorferi infection) is best made on the basis of a history of exposure to the vector tick or tick habitat and clinical findings. Clinical findings, as well as laboratory testing, vary with the stage of the disease (Table 5). Diagnosis of early-stage, localized Lyme disease can be made on the basis of erythema migrans alone without laboratory testing.4 When there is diagnostic uncertainty, positive IgG and/or IgM serology results on acute- and convalescent-phase (ie, 2 to 4 weeks after the acute phase) samples can support the diagnosis (Table 5).

Table 5. Lyme Disease: Clinical Features13 and Recommended Laboratory Testing4
Stage of Disease Clinical Features Laboratory Testing
Early-stage (localized) Erythema migrans, fever, myalgia, headache, nausea, fatigue

<2 weeks after the tick bite: testing not recommended

2–4 weeks after the tick bite: acute and convalescent 2-tiera

IgG, IgM serology (if diagnosis uncertain)

Early-stage disseminated (cardiac involvement) Atrioventricular heart block sometimes with myopericarditis; migratory pain in joints, bone, and muscle; secondary annular lesions; malaise; fatigue

2–4 weeks after the tick bite: acute and/or convalescent 2-tiera IgG, IgM serology

>4 weeks after the tick bite: acute and/or convalescent 2-tiera IgG serology

Late-stage disseminated (neurologic and/or arthritic involvement) Encephalopathy; polyneuropathy; lymphocytic meningitis; prolonged, chronic arthritis; lymphocytoma; fatigue Acute and/or convalescent 2-tiera IgG serology in serum; consider serology and/or detection of B burgdorferi DNA in CSF or synovial fluid

a Two-tier testing is a follow-up of a positive or equivocal EIA with a Western blot test as recommended by the Centers for Disease Control and Prevention and the Association of State and Territorial Public Health Laboratory Directors.14

Test Selection for Disseminated Lyme Disease
In the absence of erythema migrans, Lyme disease cannot be diagnosed on the basis of disseminated disease manifestations alone, because these symptoms are nonspecific.4 Diagnosis requires demonstration of seropositive test results.4 Combined IgG and IgM testing is recommended for patients 2 to 4 weeks after the tick bite (Table 5).4 Western blot testing is recommended as a confirmatory test for all specimens positive or equivocal by EIA.14

Immunoassays used to detect Lyme disease antibodies utilize whole spirochete preparations or purified antigens, such as VlsE and PepC10. The VlsE protein contains the C6 peptide, and PepC10 is a major target of IgM induced by B burgdorferi infection. The VlsE+PepC10 antibody (IgG+IgM) test is used to detect infection from both American and European Borrelia species and to reduce false positives that may be caused by antibodies cross-reacting with similar organisms.15

Methods that detect B burgdorferi DNA may be used to support the diagnosis of disseminated Lyme disease. For neurologic Lyme disease, DNA detection in cerebrospinal fluid (CSF) has a sensitivity of 38% (≥93% specificity).16 Alternatively, intrathecal antibody production using a CSF to serum antibody ratio may be used (sensitivity, 75%; specificity, 97%).17 Positive DNA findings in synovial fluid supports the diagnosis of Lyme arthritis (sensitivity, 78%; specificity,100%).16 However, because spirochetemia is typically transient or absent, detection of B burgdorferi DNA in whole-blood specimens has low clinical sensitivity (14%) rendering negative results non-informative.16

Test Interpretation
IgM antibodies may be present within a few weeks of disease onset, whereas IgG antibodies are produced later. A positive IgM result as determined by 2-tier testing, in conjunction with a negative IgG result, is presumptive evidence of early infection unless obtained on a specimen collected more than 1 month following onset. In the latter scenario, a positive IgM finding is more likely to represent a false-positive unless IgG is also positive. A positive IgG result by 2-tier testing is required to confirm the diagnosis of disseminated disease.4

The interpretation of Western blot antibody assays is based on the number of positive bands: 2 of 3 bands (23, 39, 41kDa) for IgM positivity and 5 of 10 bands (18, 23, 28, 30, 39, 41, 45, 58, 66, or 93 kDa) for IgG positivity. The Western blot is to be used only following initial EIA testing, and positive results confirm B burgdorferi infection.4

False-positive antibody test results may be due to vaccination, infectious mononucleosis, systemic lupus erythematosus, or other diseases caused by spirochetes such as yaws, pinta, and relapsing fever. Additionally, positive antibody test results, including those from the VlsE+PepC10 EIA, may be due to active or past B burgdorferi infection.

Negative serology results may indicate lack of infection or lack of seroconversion, which may occur if samples are collected too early after disease onset or when early antibiotic therapy blunts the antibody response. Untreated patients who continue to be symptomatic but are seronegative for 6 to 8 weeks are unlikely to have Lyme disease, and another diagnosis should be considered.4

Expression of paired CSF and serum B burgdorferi antibody results as an antibody index can be used as an aid in the diagnosis of neuroborreliosis. An index >1.2 is deemed positive for intrathecal antibody production if accompanied by a control antibody index <1.0 and an albumin ratio <0.0078. Elevation of either the control antibody index, the albumin ratio, or both may indicate leakage of antibody across the blood-brain barrier and a falsely elevated B burgdorferi antibody index.

In a seropositive patient, positive DNA results support the diagnosis of Lyme disease.4  However, in a seronegative patient, positive results should be interpreted with caution.4

Tick-borne Rickettsial Diseases (TBRDs)

Ehrlichioses and anaplasmosis are characterized by infection of leukocytes, in which the causative agents multiply in cytoplasmic membrane-bound vacuoles called morulae. E ewingii and A phagocytophilum infect granulocytes, whereas E chaffeensis infects monocytes. Thus, visualization of morulae on a routine blood smear may provide the first clue for diagnosis and help differentiate HME from HGA and E ewingii infection. Positive results may be seen in up to 60% of patients with HGA and to a lesser extent in patients with HME.7

In patients with RMSF, increased band neutrophil counts are generally observed on a complete blood count (CBC), and since they are less commonly seen with viral infection, aid in the differential diagnosis. Symptomatic patients have an increased likelihood of HGA when platelets, WBCs, or both are reduced; the relative risk was 5.2 when the WBC count was <2.5 x 109 cells/L and 10.3 when the platelet count was <100 x 109 cells/L.18 Laboratory test results associated with the various TBRDs are listed in Table 6.

Table 6. Laboratory Confirmation of Tick-borne Rickettsial Diseases7
Disease Common Laboratory Abnormalities Confirmatory Laboratory Tests Laboratory Criteria for Confirmation of Diagnosis

Rocky Mountain

spotted fever

• WBC count N

• Platelet count

• Sodium slight

• Transaminases slight

Acute and convalescent

serology or

4-fold increase in

antibody titer

R rickettsii DNA Detected

Human monocytic ehrlichiosis

• WBC count in 53%

• Platelet count in 94%

• Transaminases (2–8

 times ULN)

Acute and convalescent serology or

4-fold increase in antibody titer

E chaffeensis DNA or

Detected

Identification of morulae
in WBCs and serology

Morulae detected and positive antibody titer

Human granulocytic anaplasmosis

• WBC count in 53%

• Platelet count in 94%

• Transaminases (2–8

times ULN)

Acute and convalescent serology or

4-fold increase in antibody titer

A phagocytophilum DNA
or

Detected

Identification of morulae in WBCs and serology

Morulae detected and positive antibody titer

Ehrlichia ewingii infection

• WBC count

• Platelet count

• Transaminases

E ewingii DNA

Detected

N, normal; , increased; , decreased; ULN, upper limit of normal.

Laboratory confirmation validates the accuracy of the presumptive diagnosis and is important from an epidemiology and public health perspective. Confirmatory laboratory testing for TBRDs  includes serology and highly specific nucleic acid detection (Table 6). Immunofluorescence assays (IFA) are considered the gold standard for TBRD serology testing.7 A 4-fold rise in titer of IgG or IgM in paired acute and convalescent samples collected 2 to 3 weeks apart is essential to confirm acute infection. Most patients have positive IgG or IgM antibody by the second week of illness. For RMSF, IgG and IgM increase concurrently; IgM wanes after 3 to 4 months, whereas IgG persists for 7 to 8 months.

Detection of DNA in whole blood is especially useful for confirming HGA, HME, and E ewingii infection because these organisms infect circulating leukocytes. For RMSF, detection of R rickettsii in blood is more likely in advanced disease or fulminant infection. Whereas positive results confirm TBRD, negative results do not exclude the diagnosis.

Tick-borne Non-Rickettsial Diseases
Colorado Tick Fever
Leukopenia is characteristically seen in a CBC, and thrombocytopenia may be present. Acute and convalescent serology should be considered for patients with clinically suspected Colorado tick fever (Table 7). A 4-fold rise of IgG or IgM titer in paired acute and convalescent samples confirms the diagnosis; the detection of IgM indicates acute infection.

Table 7. Laboratory Confirmation of Tick-borne Non-Rickettsial Diseases5,6,8-11
Disease Common Laboratory Abnormalities Confirmatory
Laboratory Tests
Laboratory Criteria for Confirmation of Diagnosis
Colorado tick fever

• WBC count

Platelet count ±

Acute and convalescent serology 4-fold increase in antibody titer; positive IgM antibody titer
Q fever

• Transaminases

(2–10 times ULN)

Platelet count ±

Acute and convalescent serology or 4-fold increase in phase II IgG or IgM antibody titer by IFA or phase II IgG titer ≥1:128 in convalescent seraa
C burnetii DNA (PCR) or Detected
C burnetii IHC staining or Detected
C burnetii culture Isolated
Tularemia

Transaminases ±

Acute and convalescent serology 4-fold increase in antibody titer
Tick-borne relapsing fever

• Platelet count

Acute and convalescent serology 4-fold increase in antibody titer
Babesiosisc

• Hematocrit
• Reticulocyte count
• Platelet count
Transaminases ±

Light microscopy of stained blood smears (Giesma, Wright, or Wright-Giesma) or Identification of Babesia organisms in RBCs
Nucleic acid amplification of Babesia DNA or Detected

Isolation of Babesia organisms by animal inoculation from whole blood

Isolated

IFA indicates immunofluorescence assay; PCR, polymerase chain reaction; IHC, immunohistochemistry; ULN, upper limit of normal; ↑, increased; ↓, decreased; ±, may be present.
a These criteria refer to acute Q fever. Laboratory confirmation of chronic Q fever requires 1 of the following: phase I IgG titer ≥1024 by IFA; PCR detection of C burnetii DNA; IHC detection of C burnetii; or culture.6
b Demonstration of at least 1 of the following provides supportive but not confirmatory laboratory evidence of babesiosis: B microti total Ig or IgG antibody titer ≥1:256 by IFA (≥1:64 for epidemiologically linked blood donors or recipients);
B microti IgG by immunoblot; B divergens total Ig or IgG titer ≥1:256 by IFA; or B duncani total Ig or IgG ≥1:512 by IFA.5

Q Fever
C burnetii infection exhibits 2 antigenic phases (I and II) that are valuable in diagnosing and staging Q fever. Acute disease is characterized by elevated phase II antibodies, whereas chronic disease is reflected by phase I antibodies. Phase II antibodies may be detected within 2 weeks of infection, and most patients have detectable antibody within 3 weeks.11 Diagnosis of acute Q fever can be based on the serologic evidence, IHC staining of C burnetii, PCR detection of C burnetii DNA, or culture (Table 7). Samples for PCR must be obtained within the first 2 weeks of infection and before (or soon after) administration of antibiotics. For patients with no laboratory evidence of infection, alternative causes should be sought; however, treatment should not be interrupted on the basis of negative serology findings.

For patients with acute infection and low risk for chronic infection, clinical and serologic evaluations should be repeated at around 6 months. For patients with predisposing risk factors for chronic disease, these assessments should be repeated at 3-month intervals, beginning at 3 months after diagnosis and continuing for 2 years.6 Diagnosis of chronic Q fever requires clinical evidence (including organ involvement) in addition to laboratory evidence (phase I IgG titer ≥1024; PCR detection of C burnetii DNA; IHC detection of C burnetii; or culture). For patients with positive laboratory results but inconclusive clinical evidence, a focus of infection should be sought. Otherwise, monitoring can be continued. Patients with clinical and laboratory evidence of chronic Q fever are treated with doxycycline for 18 to 24 months, depending on the clinical manifestations, with ongoing clinical and serologic evaluation.6 A reduction in titer is suggestive of therapeutic response. Patients are considered to have recovered when symptoms have resolved, phase I IgG titer has decreased at least 4 fold, and phase II IgM is undetectable. If patients have recovered with the initial 18 to 24-month course of treatment, therapy can be discontinued but clinical and serologic monitoring should be continued for at least 5 years. For those who do not demonstrate recovery, treatment and monitoring should be continued and expert consultation sought.

Tularemia
F tularensis serology testing can confirm a diagnosis of tularemia (Table 7). An antibody titer 1:20 is suggestive of acute or past infection and a 4-fold increase in titer between acute and convalescent sera collected 2 to 3 weeks apart is considered diagnostic. Antibody begins to appear 2 to 3 weeks post-onset and peaks at about 5 weeks. However, up to 30% of patients infected for 3 weeks have negative serology results.12 Because Brucella antibodies cross-react with this test, positive specimens should also be tested for Brucella antibody.

Tick-borne Relapsing Fever (TBRF)
Diagnosis of TBRF is made by the detection of spirochetes in the patient’s blood during periods of high fever (sensitivity 70%).3 Diagnosis is confirmed by serology testing. The presence of B hermsii IgM titers 1:16 are associated with acute infection, while IgG titers 1:64 reflect later stages of disease. Single IgG titers 1:64 are considered presumptive evidence of infection and a 4-fold increase in titer between acute and convalescent sera provides evidence of recent or current infection (Table 7). Because other Borrelia and Treponema species cross-react in the IFA test, positive specimens should be tested for antibodies to these organisms.

Babesiosis
The current case definition for babesiosis requires the presence of clinical evidence (fever, anemia, or thrombocytepenia) and/or at least one subjective symptom (chills, sweats, headache, myalgia, or arthralgia).5 Laboratory confirmation of infection may include microscopic identification or nucleic acid amplification detection of Babesia spp DNA (Table 7).5 Serologic studies may provide supportive laboratory evidence (Table 7). Specific B microti antibodies are usually present by the time the patient exhibits parasitemia and invariably within 4 weeks of onset, unless the patient is immunocompromised.

Additional laboratory abnormalities may include hemolytic anemia with an elevated reticulocyte count, thrombocytopenia, proteinuria, and elevated levels of liver enzymes, blood urea nitrogen, and creatinine.

Laboratory test results, combined with clinical symptoms, are used to make treatment decisions.4 Treatment is recommended in symptomatic patients when babesial parasites have been identified or DNA results are positive.4 Treatment is not recommended in symptomatic patients whose blood is negative for babesial parasites or DNA, even if serology testing is positive. Also, treatment is not recommended for asymptomatic individuals, regardless of laboratory test results. Asymptomatic individuals with positive babesial smears and/or DNA results should have these tests repeated, and treatment should be considered if repeat testing is positive >3 months later.

References [return to contents]

  1. Centers for Disease Control and Prevention (CDC). Summary of Notifiable Diseases—United States, 2010. MMWR Morb Mortal Wkly Rep. June 21, 2012;59:1-111.

  2. Bratton RL, Corey GR. Tick-borne disease. Am Fam Physician. 2005;71:2323-2330.

  3. Dennis DT, Hayes EB. Relapsing fever. In: Kasper DL, Braunwald E, Fauci AS, Hauser SL, Longo DL, Jameson JL, eds. Harrison’s Principles of Internal Medicine, 16th ed. New York, NY: McGraw-Hill; 2005:991-995.

  4. Wormser GP, Dattwyler RJ, Shapiro ED, et al. The clinical assessment, treatment, and prevention of Lyme disease, human granulocytic anaplasmosis, and babesiosis: Clinical Practice Guidelines by the Infectious Diseases Society of America. Clin Infect Dis. 2006;43:1089-1134.

  5. Centers for Disease Control and Prevention (CDC). Babesiosis surveillance - 18 States, 2011. MMWR Morb Mortal Wkly Rep. 2012;61:505-509.

  6. Anderson A, Bijlmer H, Fournier PE, et al. Diagnosis and management of Q fever—United States, 2013: recommendations from CDC and the Q Fever Working Group. MMWR Recomm Rep. 2013;62(RR-03):1-30.

  7. Chapman AS, Bakken JS, Folk SM, et al. Diagnosis and management of tick-borne rickettsial diseases: Rocky Mountain spotted fever, ehrlichiosis, and anaplasmosis—United States. MMWR Recomm Rep. March 31, 2006;55:1-27.

  8. Klasco R. Colorado tick fever. Med Clin North Am. 2002;86:435-440.

  9. Dworkin MS, Schwan TG, Anderson DE. Tick-borne relapsing fever in North America. Med Clin North Am. 2002;86:417-433.

  10. Krause PJ. Babesiosis. Med Clin North Am. 2002;86:361-373.

  11. Hartzell JD, Wood-Morris RN, Martinez LJ, et al. Q fever: Epidemiology, diagnosis, and treatment. Mayo Clin Proc. 2008;83:574-579.

  12. Jacobs RF. Tularemia. In: Kasper DL, Braunwald E, Fauci AS, et al, eds. Harrison’s Principles of Internal Medicine, 16th ed. New York, NY: McGraw-Hill; 2005:917-921.

  13. Depietropaolo DL, Powers JH, Gill JM. Diagnosis of Lyme disease. Am Fam Physician. 2005;72:297-304.

  14. Centers for Disease Control and Prevention. Recommendations for test performance and interpretation from the Second National Conference on Serological Diagnosis of Lyme Disease. MMWR.1995;44:590-591.

  15. Porwancher RB, Hagerty CG, Fan J, et al. Multiplex immunoassay for Lyme disease using VlsE1-IgG and pepC10-IgM antibodies: improving test performance through bioinformatics. Clin Vaccine Immunol. 2011;18:851-859.

  16. Aguero-Rosenfeld ME, Wang G, Schwartz I, et al. Diagnosis of Lyme borreliosis. Clin Microbiol Rev. July 2005;18:484-509.

  17. Blanc F, Jualhac B, Fleury M, et al. Relevance of the antibody index to diagnose Lyme neuroborreliosis among seropositive patients. Neurology. 2007;69:953-958.

  18. Bakken JS, Aguero-Rosenfeld ME, Tilden RL, et al. Serial measurements of hematologic counts during the active phase of human granulocytic ehrlichiosis. Clin Infect Dis. 2001;32:862-870.
     

Polymerase chain reaction (PCR) is performed pursuant to a license agreement with Roche Molecular Systems, Inc.

Content reviewed 06/2013

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