Although Lyme disease has become the most talked about tickborne illness in the United States, there are several other equally important diseases that seem to get less press: Rocky Mountain spotted fever, ehrlichiosis, tularemia, babesiosis, relapsing fever, and Colorado tick fever. Although I'll focus on the three most common — Lyme disease, Rocky Mountain spotted fever, and ehrlichiosis — tickborne disease is an important topic for any emergency physician because most of the diseases have very nonspecific presentations (at least initially), and can lead to significant morbidity and mortality. Knowing one's local epidemiology is helpful in raising suspicion about what seems like a viral syndrome but is actually a bacterial or spirochete infection.
Lyme disease is the most common tickborne illness in the United States, with more than 15,000 cases reported to the Centers for Disease Control and Prevention each year. Geographically, the disease clusters along the Eastern seaboard, with some cases occurring in northern California. The causative agent is the spirochete Borrelia burgdorferi, which was identified in the early 1980s. The disease is transmitted by the bite of the deer tick (Ixodes scapularis), which must be attached for at least 36 hours for disease transmission to occur. Approximately 80 percent of patients with Lyme disease will report a rash called erythema migrans, the “classic” large (at least 15 cm) area of erythema with a target-like appearance. (This means 20 percent of patients with Lyme disease do not report or have a rash!)
Next, nonspecific symptoms consisting of headaches, myalgias, arthralgias, fatigue, and fever occurs. This is commonly referred to as stage 1. Stage 2 or early disseminated disease consists of fever, neck stiffness, multiple cutaneous annular lesions, adenopathy, and sometimes a seventh nerve palsy. Stage 3 or late disseminated disease includes arthritis, meningoencephalitis, cardiac conduction defects (AV blocks), and neurocognitive changes.
The diagnosis of Lyme disease can be clinical — the right rash in the right part of the country or with more nonspecific presentations with serology. In endemic areas, many clinicians will treat a seventh nerve palsy patient for Lyme or at least send titers. Serum or CSF IgG or IgM is used with a confirmatory Western Blot. Serologies are often negative early in the course of the disease. (New Engl J Med 2003;348:2424.)
The treatment is based on the stage of the disease, with doxycycline being the drug of choice for stage 1 or 2 disease. Many experts state that using doxycycline in children with stage 1 or 2 Lyme disease is reasonable, given the low likelihood of staining teeth and the good clinical response to this drug. Amoxicillin or cefuroxime are alternatives to doxycycline. The course of treatment should be at least 10 to 14 days for stage 1 and 14 to 21 days for stage 2. For stage 3 disease, IV ceftriaxone 1 gm/day for 28 days for adults and 100 mg/kg/day for children. The treatment of an asymptomatic deer tick bite in an endemic area is controversial, with some evidence showing benefits in a single dose of doxycycline 200 mg. (N Engl J Med 2001;345:79.)
Rocky Mountain Spotted Fever
Rocky Mountain spotted fever is the second most common tickborne illness in the U.S. The bacterium Rickettsia rickettsii was first isolated in the early 1900s, and is a gram-negative intracellular coccobacillus transmitted by the bite of the dog tick (eastern U.S.), the wood tick (western U.S.), or the Lone Star tick (southwestern U.S.). The most common states that see Rocky Mountain spotted fever are North Carolina, Oklahoma, Kansas, Missouri, and Arkansas. In contrast to Lyme disease, the tick needs to feed for only six hours for transmission to occur. Children between 5 and 9 are most commonly affected. (Ann Rev Public Health 1998;19:237.)
Initial signs and symptoms include fever, headache, nausea and vomiting, myalgias, and sometimes cough, sore throat, and abdominal pain. Eighty to 90 percent of patients have the pathognomonic rash, which begins two to four days after the onset of symptoms. The rash is described as a blanching maculopapular rash on the palms and soles, spreading to the wrists and ankles and changing to petechiae and purpura; later, it moves to the trunk and face. Late disease can lead to meningoencephalitis, congestive heart failure, or shock. Mortality can be 25 percent if untreated and five percent with treatment.
The diagnosis, like Lyme disease, can be clinical, but often serology must be used. Routine labs are nonspecific, with a normal WBC count. Hyponatremia and thrombocytopenia are most common. If CSF is obtained, it is frequently abnormal, with elevated protein and WBC count. Serum ELISA and latex agglutination studies may be sent, but treatment should not be withheld pending these results in strongly suspicious cases.
Skin biopsies of the rash with immunofluorescent staining also can be used. The treatment is doxycycline, with stronger recommendations for using this drug in children. The commonly-held belief that the tetracyclines stain developing teeth came from studies in the 1960s with multiple courses of tetracycline. More recent studies have shown no staining in children receiving tetracyclines. (MMWR 2006;55[RR04];1.)
The Centers for Disease Control and Prevention and the American Academy of Pediatrics have identified doxycycline as the drug of choice in Rocky Mountain spotted fever in children. (MMWR 2006;55[RR04];1 and Red Book: Report of the Committee on Infectious Diseases. 26 ed. Elk Grove Village, IL; 2003:532.) The adult dose is 100 mg PO BID for at least five to seven days, but must continue for three days after the fever has subsided; the pediatric dose is 2.2 mg/kg BID.
There are two subtypes of human ehrlichiosis, human monocytic (HME), and human granulocytic ehrlichiosis (HGE); clinically they are indistinguishable but are caused by two different organisms, Ehrlichia chaffeensis and Anaplasma phagocytophilum, respectively. HME primarily occurs in the south-central and southern U.S., and is transmitted by the bite of the Lone Star tick or dog tick. HGE occurs in the upper midwestern and northeastern U.S. and is transmitted by the deer tick. The signs and symptoms begin with the usual nonspecific headache, fever, cough, malaise, and in HME, a rash. Approximately 30 percent of patients with HME and very few patients with HGE will have a rash.
The rash is either maculopapular, macular, or petechial affecting the trunk and upper extremities, making clinical differentiation between Rocky Mountain spotted fever and HME difficult. (Remember, however that Rocky Mountain spotted fever primarily occurs in children, while ehrlichiosis occurs in adults.) Laboratory findings with ehrlichiosis include thrombocytopenia, leukopenia, and elevated transaminases. The diagnosis is again either clinical (by signs and symptoms plus suspicious laboratory values) or by blood smear (not sensitive), immunofluorescent antibody, or ELISA testing. It is very important to note that the latter two tests are often negative in the first seven days of the disease, making empiric treatment an important consideration.
It is important for us to keep in mind that adding one of these diseases to your differential of what seems like a viral syndrome is good medicine and impressive to your infectious disease colleagues.