CDC develops guidelines for tickborne diseases

May 2006

Low-cost, effective antimicrobials against tickborne rickettsial diseases are available, according to a CDC report, and are particularly effective when administered early in the course of disease. However, early signs are nonspecific, and many symptoms mimic viral illnesses.

Focusing on epidemiology, clinical assessment, diagnosis and treatment, the CDC’s viral and rickettsial zoonoses branch developed guidelines for the diagnosis and management of these diseases.

Tickborne disease background

Rocky Mountain spotted fever (RMSF), human monocytotropic, or monocytic, ehrlichiosis (HME), human granulocytotropic, or granulocytic, anaplasmosis (HGE) and Ehrlichia ewingii infections are all found in the United States, according to the CDC.

RMSF, HME and HGA may occur at any time throughout the year, although 90% to 93% of cases occur in April through September. A study of children in the southeastern and south central United States determined that up to 22% of children have serologic evidence of exposure to E. chaffeensis and Rickettsia rickettsii or related bacteria, which may indicate that RMSF and HME infections are more common than previously thought.

Fifty-six percent of all RMSF cases were reported from Arkansas, North Carolina, Oklahoma, South Carolina and Tennessee; however, all of the continental states except for Maine and Vermont reported cases. Dogs may often develop RMSF concurrently with other household members.

HME is most commonly reported to the CDC from Arkansas, Maryland, Missouri, Oklahoma and Tennessee, although cases have been reported from the south central part of the United States to New England.

HGA occurs more frequently than HME, and is most commonly reported in Connecticut, Maryland, Minnesota, New York and Rhode Island.

Clues for diagnosis

The CDC report recommends that clinicians obtain a detailed medical history, which may reveal clues to diagnosis.

A patient could be exposed to ticks during recreational activities. Many patients cannot recall a tick bite, and physicians should never disregard the possibility of tickborne disease when a patient does not present with a bite.

Signs and symptoms of tickborne illness are nonspecific and resemble other infectious and noninfectious diseases and include a sudden onset of chills, fever, headache, malaise and myalgia.

Adults almost always report headache and anorexia. Nausea and vomiting may occur, particularly in children with RMSF and HME. Diarrhea occurs occasionally. Children with RMSF or HME commonly report:

• abdominal pain, which is sometimes severe and may mimic appendicitis;
• altered mental status; and
• conjunctival injection.

A rash typically occurs in people with RMSF about two to four days after the onset of fever, although most patients seek medical attention before the rash appears. The rash eventually occurs in 90% of children with RMSF, and presents earlier in children than adults.

The CDC notes that obtaining a complete blood count, a comprehensive metabolic panel and an examination of peripheral blood smear are essential to diagnose these illnesses. In addition, serum samples for testing of rickettsial disease should be collected during the first week of illness, and two to three weeks later. Nonreactive serology results in the initial sample does not rule out rickettsial illness, and in fact, is often observed as most patients present for care in the first two to three days of illness, but antibodies to these agents are generally nondetectable until seven to 10 days of illness.

Treatment

Patients who may have organ dysfunction, mental status changes and severe thrombocytopenia should be hospitalized. CDC officials noted about 50% of people with tickborne disease may need to be hospitalized. Empiric treatment may be used in suspected cases.

Tickborne illnesses are susceptible to tetracyclines, and the CDC recommends oral or IV doxycycline as the first-line treatment for children and adults. When meningococcal disease cannot be ruled out, the patient should receive ceftriaxone in addition to the doxycycline.

The CDC recommends 2.2 mg/kg twice daily for children and 100 mg of doxycycline twice daily for adults.

Because a delay in treatment can lead to severe disease or death, the patient should begin receiving antibiotics immediately when a clinician suspects tickborne illness based on clinical, epidemiological or laboratory findings.

Limited numbers of ticks in endemic areas are infected with pathogenic rickettsiae; therefore, the CDC does not recommend preventative antibiotic therapy for every tick bite if patients are not ill.

Avoiding tick bites and removing attached ticks are the best disease prevention strategies, particularly during spring and early summer.

Physicians who identify a potential case of tickborne rickettsial disease should notify the local health department, which can assist with obtaining laboratory tests to confirm the diagnosis. Surveillance and reporting of tickborne rickettsial diseases are critical for studying the changing epidemiology of these diseases and for developing effective prevention strategies and public health education programs.

The guidelines were published recently in the Morbidity and Mortality Weekly Report.

For more information:

• CDC. Diagnosis and management of tickborne rickettsial diseases: Rocky Mountain spotted fever, ehrlichioses, and anaplasmosis – United States: A practical guide for physicians and other health-care and public health professionals. MMWR. 2006;55:1-27.