Tick-borne Illness: Evaluation and Management in the Emergency Department: Part II

Tick-borne Illness: Evaluation and Management in the Emergency Department: Part II

Authors:

Medley O'Keefe Gatewood, MD, Assistant Professor, Division of Emergency Medicine, University of Washington Medical Center, Harborview Medical Center, Seattle, WA.

Mitchell Kim, MD, Resident, Division of Emergency Medicine, University of Washington Medical Center, Seattle.

Peer Reviewer:

Dan Quan, MD, Department of Emergency Medicine, Maricopa Medical Center, Phoenix, AZ.

Dermacentor Variabilis

Dermacentor variabilis, also known as the American dog tick, is the vector that is most commonly associated with the transmission of Rocky Mountain spotted fever (RMSF) and tularemia. It is widely distributed on the West Coast, central-eastern United States (see Figure 1), Mexico, and Canada.¹

A related species, Dermacentor andersoni, known as the Rocky Mountain wood tick, is known to be the vector of the same diseases. It resides in the Pacific Northwest and northern Rocky Mountain states. (See Figure 2.)

Figure 1: Geographic Distribution of Dermacentor variabilis, the Dog Tick Source:US Centers for Disease Control and Prevention(CDC).Atlanta,GA,

Figure 2: Geographic Distribution of Dermacentor andersoni, the Wood Tick Source:US Centers for Disease Control and Prevention(CDC).Atlanta,GA,

Only the adult form of the dog tick is thought to cause human disease. Adult ticks are most active in late spring through early fall, similar to other ticks. They occur primarily in the woods or areas with shrubs or long grass. Dog ticks are unable to establish an infestation within homes.^1,2

Adult dog ticks are about one-quarter inch in length, reddish-brown in color, with a gray-silver colored marking on the dorsal surface (their "shield"). Male dog ticks have this marking diffusely on their dorsal surface (see Figure 3A), whereas the female dog tick's marking is localized to the cephalad one-third of its dorsal surface (see Figure 3B). This silver-gray dorsal scutum (which does not change while feeding) and the larger size of the dog tick help distinguish this tick from Ixodes scapularis.^1,2

Figure 3A: Male Dog Tick Dermacentor variabilis The male dog tick, Dermacentor variabilis, with the characteristic graysilver marking on its dorsal surface. Source: US Centers for Disease Control and Prevention (CDC), Atlanta, GA, USA. CDC Public Health Image Library.

Figure 3B: Female Wood Tick, Dermacentor andersoni The female wood tick, Dermacentor andersoni, with the characteristic graysilver scutum on the cephalad aspect of its dorsal surface. Source: US Centers for Disease Control and Prevention (CDC), Atlanta, GA, USA. CDC Public Health Image Library.

Rocky Mountain Spotted Fever (RMSF)

RMSF is now a member of a group of illnesses termed "spotted fever rickettsioses." They are a collection of diseases that are caused by the closely related Rickettsia species that are transmitted by various arthropod vectors. Other examples include typhus (in the United States and abroad) and rickettsialpox. Rickettsia rickettsii is an obligate, intracellular, gram-negative bacillus that infects endothelial cells within vasculature. Subsequent cytotoxicity causes its characteristic purpura.^3,4

Epidemiology

Rickettsia rickettsii is transmitted by several species of ticks throughout the United States. RMSF cases have been reported in most of the contiguous United States. Although it is termed the "Rocky Mountain" spotted fever, its current incidence is highest in the south Atlantic states. The number of cases in the Rocky Mountain states dropped markedly in the 1940s for an unclear reason, and has remained so since. Its transmission can occur within 6-10 hours of tick attachment, and it may be transmitted by inhalation of contaminated aerosol in the laboratory setting.⁵

Until the early 2000s, there were roughly 600-1,200 cases of RMSF per year in the United States. This number has increased in the past decade, with 1,791 cases reported to the CDC in 2009. The peak incidence is between April and October.⁶ Outbreaks have been reported in areas where RMSF incidence is relatively rare, such as rural eastern Arizona, where the brown dog tick Rhipicephalus sanguineus is the implicated vector.⁷ RMSF is considered the most fatal tick-borne infection. In the pre-antibiotic era, it was associated with a 65-80% case-mortality rate. It is associated with a 25% mortality if left untreated, but with antibiotics, the case-mortality rate is 0.5-3%.^3,6,8

Clinical Presentation

Patients with RMSF present with symptoms about 2-14 days following the tick bite. The classic triad of fever, rash, and history of tick bite is only present in the minority of patients.⁵ Initial symptoms of fever, headaches, and myalgias occur due to bacteremia. As the bacteria invade the vascular endothelium, necrotizing vasculitis ensues, with the appearance of the classic RMSF rash. This rash is described as discrete, blanching macules (see Figure 4) that appear 2-4 days following the onset of fever. It generally appears first on the wrists/ankles and quickly spreads to the soles/palms before migrating centrally onto the trunk. These macules slowly fade over 2-3 weeks. However, approximately 10% of patients with RMSF do not have a rash at any point in their disease course.⁸

The work-up reveals lymphocytic pleocytosis in the CSF, anemia, thrombocytopenia, elevated liver tests, azotemia, and hyponatremia. Frank renal failure and CNS symptoms are markers of poor prognosis.^3,9 The clinical picture of RMSF may resemble meningococcemia, especially if patients present with meningismus. In these cases, the work-up and treatment should empirically cover both Rickettsia rickettsii and Neisseria meningitidis.

In some cases, the petechial lesions of RMSF form confluent ecchymotic areas of skin, often in the digits and genitalia. This may be complicated by necrosis with eventual gangrene.⁸ Other complications include encephalitis, ARDS, cardiac arrhythmias, coagulopathy, and GI bleeding. Long-term issues are often due to CNS damage — neuropathy, cerebellar disorders, and neuropsychiatric symptoms. Without treatment (or delayed treatment), death can occur 1-2 weeks following the onset of fever. African-American men with G6PD deficiency have the most fulminant course.

Diagnosis

RMSF is largely a clinical diagnosis. Unfortunately, clinical findings in RMSF are largely nonspecific and are similar to the presentation of many tick-borne and non-tick-borne diseases.⁹ Definitive diagnosis is made via serological tests or PCR, since Rickettsia rickettsii is notoriously difficult to culture. Antibodies cannot be detected for 7-14 days following the onset of illness. Currently, the gold standard test to diagnose RMSF is the indirect fluorescent antibody (IFA) test. Immunohistochemistry staining of skin biopsies can confirm the diagnosis. However, this is not widely available, and is more often used to confirm diagnoses at autopsy. PCR methods are available, but have poorer sensitivity than IFA.^3,9 It is currently recommended that empiric treatment be initiated if the clinical suspicion for RMSF is high, pending confirmatory test results at a future date.¹⁰

Treatment

There is a clear link between delay in treatment and mortality. This is evidenced by an increased mortality in those who present with a late-appearing rash, without a history of tick bite, or atypical symptoms of RMSF.⁵ Beginning treatment more than five days following the onset of symptoms is associated with poorer outcome.¹¹

The first-line treatment for RMSF is 7-14 days of doxycycline for both adults (100 mg BID) and children of all ages. Patients who are severely ill should be hospitalized and given intravenous doxycycline. An added benefit of doxycycline is that it covers other tick-borne organisms with clinical presentations that may be confused with RMSF.^3,10

Chloramphenicol (50-75 mg/kg/day for 7 days) has anti-RMSF activity. However, its efficacy is inferior when compared to doxycycline, it has more side effects, and it has a more complex dosing schedule. It is recommended for pregnant patients and those with tetracycline allergies. However, doxycycline should be considered in pregnant patients with severe symptoms.^3,9 There is no evidence to support the use of post-exposure prophylaxis for RMSF.¹⁰

Summary of Rocky Mountain Spotted Fever:

• Most frequently occurs in the Atlantic states;
• It presents with a characteristic rash affecting the palms and soles that migrates proximally;
• Diagnosis and empiric treatment with doxycycline should begin based on clinical findings.

Tularemia

Tularemia is an uncommon, potentially fatal zoonotic infection that is caused by a gram-negative coccobacillus Francisella tularensis.¹² It is considered a potential agent in biological weapons.³

Epidemiology

The primary tick vectors for tularemia in the United States include the dog tick, wood tick, and the lone star tick. However, it can be transmitted by other arthropods or via inhalation, laboratory exposure, ingestion of contaminated foods/water, or animal bites. More than 250 animal species are thought to be carriers of Francisella tularenis.³

Tularemia has been reported in every state in the United States except Hawaii. It is much more prevalent in south-central states; 56% of all cases in 2000 were reported from Arkansas, Missouri, South Dakota, and Oklahoma. Between 2003 and 2012, 95 to 166 cases per year have been reported in the United States. Like other tick-borne diseases, most cases were reported in the late spring to early autumn months. This disease is more prevalent in men and those with particular exposures (i.e., landscapers who cut up brush, mow lawns, etc.).^3,13,14

Clinical Presentation

Tularemia presents with an abrupt onset of fever, anorexia, vomiting, chills, headache, and myalgia following an incubation period of 1-21 days. One of the hallmarks of this disease is a high fever without a reflexive increase in pulse, a phenomenon known as pulse-temperature disparity. There are six syndromes that describe the different clinical manifestations of tularemia.^3,14

• Ulceroglandular (65-75% of all cases): This form of tularemia occurs due to cutaneous exposure to Francisella tularensis, which can occur due to tick bites, direct exposure to animals while skinning/cleaning a carcass, or secondary to an animal bite. A pruritic/tender papule occurs at the site of injury, which progresses to an indurated, pustular, nonhealing ulcer (see Figure 5) with a punched-out appearance that later develops a necrotic base. Regional lymphadenitis occurs with the ulcer as the organisms migrate along the lymphatics. The lymph nodes may become fluctuant and drain suppurative fluid.3,14
  

  Figure 5: Ulcerative Lesion of Tularemia

  

  The ulcerative lesion on a hand of a man exposed to tularemia. This is seen at the site of cutaneous inoculation. Source: US Centers for Disease Control and Prevention (CDC), Atlanta, GA, USA. CDC Public Health Image Library.

• Glandular (5-10% of all cases): This form is similar to ulceroglandular tularemia, except lymphadenopathy occurs without the presence of the characteristic skin ulcer.14,15
• Oculoglandular (approximately 1% of all cases): This occurs when the portal of entry is the conjunctiva. Painful, purulent conjunctivitis ensues, with nodule formation and ulceration. Patients may present with only ocular symptoms before regional lymphadenopathy is present. Preauricular lymphadenopathy is unique to tularemia and helps distinguish it from other infectious diseases.14
• Oropharyngeal (< 5% of all cases): This syndrome occurs following ingestion of infected food or water. It presents as a febrile illness with exudative pharyngitis and oral ulcers. It can mimic URI.3
• Typhoidal: This syndrome is considered rare, but accounted for approximately 10% of all cases in one series.15 This presents in older patients as a viral syndrome, which leads to sepsis, as it is the presentation of tularemic bacteremia. Blood culture growth, ulcers, and lymphadenopathy may be absent. Ultimately, this can lead to septic shock, and mortality is high without appropriate treatment.14 Meningitis and pneumonia can complicate this syndrome.16
• Pulmonary: This syndrome occurs secondary to inhalation of infectious particles or via hematogenous spread to the lungs from cutaneous/lymphatic sources. It must be considered in the diagnosis in patients with an appropriate exposure history and atypical pneumonia unresponsive to conventional treatment. Patients present with dyspnea, hemoptysis, and/or chest pain. The chest X-ray is generally abnormal with infiltrates and/or pleural effusion.14

Diagnosis

Oropharyngeal swabs, sputum samples, or blood can be sent for culture. Cultures are often negative, and it may take up to two weeks to appear. In addition, laboratories must take special precautions to prevent personnel from being infected during the culture process.^16,17

A presumptive diagnosis can be made with direct immunofluorescent antibody assay, latex/tube agglutination assay, or via a PCR. Immunohistochemistry of histological specimen can be used to directly visualize the bacterium.^3,17,18

Treatment

Treatment recommendations for tularemia have been driven by cure/relapse rates seen in multiple case series and anecdotal data. Aminoglycosides, chloramphenicol, tetracyclines, and fluoroquinolones have been shown to be effective in tularemia. In general, streptomycin is the treatment of choice for severe tularemia that is not complicated by meningitis. Treatment is generally for 7-14 days. Gentamicin is a suitable alternative and is used preferentially over streptomycin.¹⁷

The FDA has approved tetracyclines as an alternative in patients with mild to moderate tularemia. The preferred regimen is doxycycline (100 mg BID) for at least 14 days. Although it is not FDA approved, oral ciprofloxacin has been shown to be effective in patients of all ages.^17,18 Chloramphenicol with streptomycin (or with gentamicin if streptomycin is not available) is used for tularemic meningitis. Chloramphenicol is generally not used as monotherapy for tularemia.¹⁶

The recommended post-exposure prophylaxis regimen for tularemia is oral doxycycline (100 mg BID) or ciprofloxacin (500 mg BID) for 14 days. This includes laboratory personnel, who may have direct exposure to the organism. Tularemia is not transmitted from person to person.¹⁹

Implications for Public Health

Tularemia caused major water-borne epidemics in Europe and Asia during the 20th century. The concern for the use of tularemia as a biological weapon surfaced following the events of 9/11. The Working Group on Civilian Biodefense recommended that in a mass-casualty situation, exposed patients should receive prophylactic doses of oral doxycycline or ciprofloxacin. Clothes and exposed skin should be washed with soap and water. Standard precautions should be employed in interacting with exposed patients.¹⁹

Although a biological attack with tularemia has not come to fruition, tularemia is a potential bioterrorism agent due to its extreme infectivity (inoculation of 10 organisms can cause disease), ease of dissemination, and capacity to cause extreme morbidity and mortality. Since the emergency department is likely the first place many of these patients will present following exposure, providers should be on the look out for concerning patterns and employ treatment as mentioned above.

Summary of Tularemia:

• Widely prevalent — reported in almost all states, and epidemic throughout the world;
• Tularemia begins as a nonspecific illness, which progresses to one of six different syndromes;
• Most frequently, there is an ulcerative lesion with associated adenopathy;
• It is considered a potential biological weapon;
• Diagnosis is made by serology;
• Intravenous streptomycin is the treatment of choice.

Colorado Tick Fever

Colorado tick fever is a viral illness caused by an RNA virus, Colorado tick fever virus (CTFV). The true reservoir for this virus is the wood tick, Dermacentor andersoni, and occurs in the western United States and southern Canada at an altitude of 4,000-10,000 feet. Unlike Lyme disease or Rocky Mountain spotted fever, a brief bite from a wood tick is sufficient to transmit the virus. There are 200-400 cases of tick fever reported every year, most commonly in the summer months.^20,21

Clinical Presentation

Following an incubation period of 3-5 days, CTFV causes a self-limited febrile illness including chills, headache, myalgia, and lethargy. Meningoencephalitis, hemorrhagic disease, pericarditis, myocarditis, orchitis, and pneumonia, although rare, have been reported. Rash is uncommon. Half of the patients will have symptoms that improve for 1-2 days followed by recurrence of fever ("saddleback fever"). The total duration of illness is usually 7-10 days. In Colorado, Colorado tick fever is much more common than RMSF.^20,22

Diagnosis and Treatment

Laboratory testing shows leukopenia, thrombocytopenia, and the presence of atypical lymphocytes. Reverse transcriptase PCR can be used to detect the virus in the first week of symptoms, or serological tests can be performed (ELISA, fluorescent antibody tests) greater than two weeks after symptom onset. Viremia lasts approximately four weeks, which allows detection for a prolonged period of time. The infection is self-limited in humans. Treatment is supportive.^20-22

Summary of Colorado Tick Fever:

• Causative pathogen is the Colorado tick fever virus;
• Presents as a self-limited febrile illness;
• Diagnosis is made by detecting viral genome in the patient serum or by serology;
• Treatment is supportive.

Tick Paralysis

Tick paralysis, also referred to as tick toxicosis, causes ascending motor neuropathy with sensory sparing. The etiological agent is a toxin that is carried in the saliva of more than 40 species of hard-bodied ticks. In the United States, it is most commonly caused by Dermacentor variabilis and Dermacentor andersoni. Although it occurs throughout the United States, it is most prevalent in the Pacific Northwest, West Coast, and in the Southeast.^20,23

Tick toxicosis is a rare condition. The true incidence is unknown since it is not a reportable disease. One series reported 33 cases over 60 years in Washington state. It preferentially affects young girls who are younger than 8 years old between the months of March and July. When found, ticks are often located on the scalp or along the hairline.²³

Clinical Presentation

Five to seven days after tick attachment, tick paralysis presents with a prodrome of restlessness, irritability, lethargy, and weakness, followed by ataxia that progresses to symmetric, ascending flaccid paralysis. The disease course is acute, with progression to upper extremity, and respiratory weakness occurring over the course of 1-2 days. There is hypo/areflexia without any changes in mentation or sensory function. Ophthalmoplegia and bulbar dysfunction can occur. Without intervention, patients die of respiratory failure.

Patients are typically afebrile and have no CSF changes. Nerve conduction studies are consistent with demyelination and loss of motor axons.^20,23,24

Diagnosis and Treatment

The identification and removal of the tick leads to rapid resolution of symptoms over 24-48 hours. This may require looking at the scalp using a fine-toothed comb and inspecting the axilla and perineum for the tick. The tick should be removed in the usual fashion. If necessary, supportive treatment with mechanical ventilation can be provided until the tick is found.²⁴

Summary of Tick Paralysis:

• Caused by a toxin that is transmitted through the tick's saliva;
• Presents with a prodrome of ataxia, followed by ascending, flaccid paralysis;
• Diagnosis and treatment is by identifying and removing the tick.

Amblyomma Americanum

Amblyomma americanum, the lone star tick, is primarily responsible for the transmission of human ehrlichiosis, also known as human monocytic ehrlichiosis (HME). In recent literature, it has been implicated in the Lyme disease-like illness known as southern tick-associated rash illness (STARI) and "meat allergy." It is primarily endemic to the southeastern to eastern parts of the United States.²⁵ (See Figure 6.)

The lone star tick gets its name from the conspicuous spot on the dorsal surface of the female body. (See Figure 7.) They feed on humans during all stages of life, allowing them to cause disease throughout the year. Unlike the bites of other disease-causing ticks, the bite of the lone star tick can cause significant irritation and pain.²

Figure 6: Geographic Distribution of the Lone Star Tick, Amblyomma americanum Source: US Centers for Disease Control and Prevention (CDC). Atlanta, GA.

Figure 7: Female Amblyomma americanum Tick The female Amblyomma americanumwith its characteristic white spot on its dorsum. Source: US Centers for Disease Control and Prevention (CDC), Atlanta, GA, USA. CDC Public Health Image Library.

Ehrlichiosis

Ehrlichiosis is a zoonotic disease that is clinically similar to anaplasmosis. It is caused by an obligate, intracellular, gram-negative organism. The lone star tick is the most common transmitter of Ehrlichia chaffeensis, although Dermacentor variabilis (the dog tick) has been implicated in areas where the lone star tick is not endemic. Ehrlichia ewingii is primarily transmitted by the lone star tick.^3,26,27

The pathogenesis involves the infection and subsequent replication within human leukocytes by these organisms. E. chaffeensis primarily targets monocytes or macrophages (hence, HME), whereas E. ewingii targets granulocytes (similar to anaplasmosis). This is manifested by the presence of characteristic morulae within infected leukocytes.^26,27

Epidemiology

HME caused by E. chaffeensis became a reportable disease to the CDC in 1999. Since then, its incidence has increased from 200 cases in 2000 to 740 cases in 2010. Its case-fatality rate has been between 1-4%. Most cases occur between April and September when the activity of the lone star tick is at its highest. It occurs more frequently in older men and in immunocompromised patients (especially HIV/AIDS, asplenic patients, and those on immunosuppressives).^3,28

Ehrlichiosis caused by E. ewingii (also transmitted by the lone star tick) has only recently been reported in humans. The first cases were reported in four patients from Missouri in 1999. Three out of the four patients were on immunosuppressive therapy.²⁷ Four more cases were described in patients from Tennessee and Oklahoma in 2001.²⁹ Since becoming a reportable disease in 2008, only nine cases of ehrlichiosis caused by E. ewingii have been reported to the CDC.³⁰

Clinical Presentation

The clinical presentation of HME and E. ewingii ehrlichiosis is similar to HGA. Its onset begins 5-21 days following the tick bite as an undifferentiated febrile illness with abrupt fever, headaches, arthralgias, chills, and myalgias. Gastrointestinal symptoms such as nausea, vomiting, diarrhea, anorexia, and abdominal pain may also occur. Respiratory symptoms are less common. One-third of all patients ultimately develop a rash, usually one week into the illness. It is usually diffuse (sometimes affecting the palms and soles) and petechial, maculopapular, or erythematous.^3,30

Laboratory studies consistent with ehrlichiosis include pancytopenia and elevated liver transaminases. Thrombocytopenia is the most common finding. The leukopenia is characterized by early lymphopenia, followed by lymphocytosis. Anemia occurs two weeks after onset. Other laboratory findings include azotemia, electrolyte abnormalities, elevation in LDH, and elevated amylase. Approximately 60-70% of patients require hospitalization. Severe complications include ARDS, renal failure, aseptic meningoencephalitis, myocarditis, GI bleed, and DIC. A toxic shock-like syndrome may occur in HIV-infected patients. In general, complications are more frequent in the immunocompromised.^3,29

Diagnosis

The diagnosis of ehrlichiosis in the acute setting is made clinically. Patients often don't remember a tick bite. Empiric treatment should be started prior to confirmatory testing.

The quickest way of diagnosing ehrlichiosis is via thick and thin peripheral blood smears on a Wright or Giemsa stain. The presence of intracellular morulae confirms the diagnosis. The sensitivity is rather low at 2-38%. The most sensitive test in the acute phase of the illness is the PCR assay. In the following weeks, the PCR assay declines in sensitivity, and indirect immunofluorescence assay (IFA) becomes the preferred diagnostic technique. PCR and IFA are usually used in conjunction to diagnose ehrlichiosis. Lastly, culture can be used in diagnosis. E. chaffeensis can be visible in leukemic cells (HL-60 line, similar to culture for anaplasmosis) in 2-36 following inoculation. E. ewingii has not been grown in laboratory as of 2010.^3,30,31

Treatment

The first-line treatment for ehrlichiosis is doxycycline for 7-14 days in both adults (100 mg BID), and children. Treatment should begin as soon as the diagnosis is clinically suspected. If symptoms do not improve in the first few days, an alternative diagnosis should be pursued. Rifampin has been shown to be effective in some patients, although the data are less robust compared to doxycycline. It may be considered in pregnant patients, children younger than the age of 8 years, and those with a tetracycline allergy. Prophylactic therapy for asymptomatic patients with a history of tick bite is not recommended.^30,31

Summary of Ehrlichiosis:

• Ehrlichia chaffeensis is an obligate intracellular organism that can be identified as intramonocytic morula on smear;
• Patients typically present with nonspecific symptoms, similar to anaplasmosis;
• Diagnosis is made with blood smear, PCR, or via serology;
• Treatment is with doxycycline for all patients.

Southern Tick-Associated Rash Illness (STARI)

Since the mid-1980s, multiple patients in the south-central and southeastern United States have presented with ECM and flu-like symptoms without evidence of Borrelia burgdorferi infection. This Lyme disease-like disease was later associated with the bite from the lone star tick. Borrelia lonestari, a spirochete that is molecularly distinct from Borrelia burgdorferi, is now thought to be the causative agent of a disease entity known as STARI. This is also known as Master Disease and Southern Lyme disease.^3,32

Epidemiology

Cases of STARI have been reported in Alabama, Missouri, Georgia, South Carolina, North Carolina, and possibly Maryland. The exact number of cases is unknown, as the disease is not reportable. It is much more prevalent in the Southeast than Lyme disease. What is known is that approximately 1-3% of lone star ticks are infected with a spirochete, and that Borrelia lonestari has been detected in lone star ticks in Southeastern and Mid-Atlantic states.^3,32,33

Clinical Presentation

The presence of an ECM-like rash is characteristic of STARI. In comparison to Lyme disease, the rash of STARI tends to be smaller, with fewer lesions, and is more likely to have central clearing. However, at initial presentation, the rash may be indistinguishable from that of Lyme disease. STARI may present as a non-specific febrile illness with headache, fever, myalgia, and arthralgia.³³ It is less likely than Lyme disease to present with systemic findings such as meningeal signs, neuropsychiatric symptoms, or regional lymphadenopathy. There are no known late complications of STARI.³²

Diagnosis

The presence of an ECM-like rash and history of exposure to a tick in the Southeastern parts of the United States is sufficient to make a diagnosis. However, Lyme disease should be considered first if the patient has been in an endemic area. There is no serological test to diagnose STARI. There is only one case report describing the detection of B. lonestari via PCR in a skin biopsy of an ECM-like skin lesion in a patient bitten by the lone star tick. The spirochete has been cultured from the lone star tick, but has never been cultured from a human.^32,33

Treatment

As there is no way to clinically distinguish the rash of STARI from Lyme disease, empiric treatment with doxycycline, amoxicillin, or cefuroxime as indicated for Lyme disease should be initiated in patients at initial presentation.³² A case report demonstrated that STARI completely resolved in an adult man following a course of doxycycline 100 mg BID for 14 days.³⁴

Summary of Southern Tick-associated Rash Illness:

• Thought to be caused by Borrelia lonestari, a bacterium similar to the causative agent of Lyme disease;
• Presents similar to Lyme disease with ECM, but has less severe symptoms;
• It is more prevalent than Lyme disease in the southeastern states;
• Diagnosis is made clinically;
• Empirically treat as if it were Lyme disease with doxycycline, amoxicillin, or cefuroxime.

The Lone Star Tick and Allergies to Meat

Allergy to red meat is a relatively uncommon food allergy. It is unique in that symptoms may arise hours following the ingestion of the allergen.³⁵ IgE to galactose-alpha-1,3-galactose (alpha gal), a disaccharide found in the cells of nonprimate mammals, has been found in individuals with meat allergies.³⁶

It has recently been hypothesized that exposure to tick salivary proteins can cause a cross sensitization to alpha gal. In the Southeastern United States, the bite from a lone star tick appears to precede the development of an allergy to red meat. A similar correlation between tick bites and red meat allergies have been demonstrated in other areas around the world, including Europe and Australia.^35,36

Ornithodoros Species: Soft-bodied Ticks

"Soft-bodied" ticks belong to the genus Ornithodoros. They are different from the hard-bodied ticks described in previous sections in that their bites are usually brief (less than 30 minutes). They live within rodents' dwellings, and humans come into contact with them when they sleep in rodent-infested buildings. Because these ticks have life spans in the range of 10-20 years, a home can remain permanently infested unless steps are taken to eradicate the rodent burrow.³⁷ In the United States, ticks from this genus are the vectors that transmit tick-borne relapsing fever (TBRF).

There are three species of Ornithodoros (see Figure 8) in the United States that are responsible for the cases of TBRF. Ornithodoros hermsii and Ornithodoros turicata cause the most cases. Ornithodoros parkeri is a less common transmitter of TBRF. O. hermsii and O. parkeri are typically found in the coniferous forests of mountainous regions in the western United States at elevations of 1,500-8,000 feet. O. hermsii, the most common vector, preferentially feed on humans that come into close contact with their natural hosts, small rodents, near freshwater lakes. O. turicata is found in the drier regions in south-central United States, often in caves.^3,38

Tick-borne Relapsing Fever (TBRF)

In the United States, the three Borrelia species that cause TBRF are named after the tick that carries it: Borrelia hermsii, Borrelia parkeri, and Borrelia turicata. Relapsing fever in other parts of the world is transmitted by ticks or by the human body louse (louse-borne relapsing fever, LBRF). Louse-borne relapsing fever is an important cause of morbidity and mortality in crowded areas of the world with poor hygiene and nutrition.³⁸ LBRF is caused by another Borrelia species, Borrelia recurrentis.³⁹

Relapsing fever is an aptly named disease; it is characterized by recurring episodes of a nonspecific febrile illness. This occurs because the Borrelia organisms repeatedly change their surface antigen in response to selection pressure within the host. This leads to repeated episodes of spirochetemia, which repeatedly stimulate the host immune system into producing recurrent episodes of a febrile illness.³⁹

Epidemiology

TBRF is found throughout the Americas, Europe, Asia, and Africa. In the United States, it is endemic to the Western states and the southcentral regions. The most common exposure sites are limestone caves of Texas and the forests of the major mountain ranges in the West, including the Cascades, Rockies, and Sierra Nevada ranges. It is typically not reported east of Texas, and only one case in Wyoming.³⁹

A total of 450 cases of TBRF were reported between 1977 and 2000. This is likely an underestimation of its true incidence. Its peak incidence occurs between November and January in Texas, and between June and September in the rest of the Western United States.^3,38 Isolated cases of transmission through blood transfusions, IV drug use, and laboratory work have been reported.³⁹

Clinical Presentation

Relapsing fever presents as an acute-onset febrile episode associated with nonspecific symptoms, including chills, headache, myalgia, arthralgia, nausea, vomiting, and abdominal pain. This follows an incubation period lasting an average of seven days. Patients are rarely aware of the tick bite. The febrile episode ends with "crisis" consisting of two phases. During the "chill phase," patients experience a fever that may be as high as 41.5°C associated with an altered mental status, tachypnea, and tachycardia, which lasts 10-30 minutes. This is followed by a "flush phase," with diaphoresis, normalization of body temperature, and transient hypotension. The entire febrile episode lasts three days on average. An afebrile period of approximately seven days associated with fatigue occurs before another febrile episode occurs. Subsequent episodes tend to be less severe. Without treatment, three to five febrile episodes occur before the disease resolves. Some patients may present with a petechial or maculopapular rash, meningeal signs, and hepatosplenomegaly. Neurological complications (meningismus, cranial nerve palsies) are more frequent with B. turicata infections than with other causes of TBRF. Laboratory work-up tends to be nonspecific, and thrombocytopenia, hematuria, proteinuria, hyperbilirubinemia, and mild coagulopathy are the most common findings.^3,40

Severe complications related to TBRF include ARDS, renal failure, myocarditis, anterior uveitis, and meningitis. There is no association between hemorrhage and the thrombocytopenia seen in TBRF. Death due to TBRF in the United States is rare, and it typically affects newborns of mothers affected with relapsing fever.³⁹

Diagnosis

Visualizing the Borrelia spirochetes on a smear of the peripheral blood, bone marrow, or CSF of an infected patient confirms the diagnosis of TBRF. The appearance of the spirochetes on Wright/Giemsa stain or dark field microscopy is morphologically similar to the Borrelia spirochetes seen in Lyme disease. The sensitivity of this test is highest during the first febrile episode.⁴⁰ Other methods include direct/indirect immunofluorescence staining of the Borrelia, or by inoculating patients' blood into mice to amplify the number of spirochetes. There are only a few laboratories capable of performing serological tests to confirm the diagnosis, and this test is marred by poor specificity.³⁹

Treatment

Tetracycline 500 QID for 10 days (IV if PO is not tolerated) is the recommended treatment regimen for adults. Erythromycin can be used if tetracyclines are contraindicated. Intravenous ceftriaxone (2 grams per day for 10-14 days) is recommended for patients with CNS involvement. Children younger than 8 years old and pregnant patients should be treated with IV penicillin G (600,000 IU daily) or erythromycin (500 mg QID).^39,40

Patients should be monitored for the first 2-4 hours of treatment for Jarisch-Herxheimer reaction (JHR), reported to occur in 54% of patients who were treated for TBRF.⁴¹ This presents with elevation of body temperature, hypotension, chills, and rigors. JHR occurs due to a massive cytokine release that occurs as the spirochetes clear from the circulation. Although no deaths due to JHR in patients with TBRF have been reported, patients with this reaction should be monitored closely.³⁹ Post-exposure prophylaxis with a five-day course of doxycycline (200 mg first day, 100 mg for the following 4) is efficacious in preventing TBRF in patients with a presumed exposure.⁴²

Summary of Tick-borne Relapsing Fever:

• Most prevalent on the West Coast and south-central United States;
• Presents with multiple episodes of nonspecific febrile illness. This may be complicated by multi-organ dysfunction;
• Diagnosis is via direct visualization of Borrelia spirochetes on body fluid smear or via serology;
• Tetracycline is the recommended treatment for nonpregnant adults;
• Penicillin G is recommended for children younger than 8 years old and pregnant women.

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