TAKE-HOME MEDICAL GRAND ROUNDS WILLIAM S. WILKE, MD, EDITOR POINTS FROM LECTURES BY CLEVELAND CLINIC AND VISITING FACULTY Tick trouble: Overview of tickrborne diseases ALAN J. TAEGE, MD positive until several weeks after the patient Department of Infectious Diseases, Cleveland Clinic has been infected; therefore, these tests must be used for confirmation, not screening. • ABSTRACT It is important for physicians to learn Tick-borne diseases can be severe or about the varying clinical characteristics and even fatal, but when identified early, the epidemiology of these diseases. In this most can be easily treated. Tick-borne article, I will first call attention to three of the diseases often present with nonspecific less familiar tick-borne diseases: Rocky symptoms. Therefore it is important for Mountain spotted fever, ehrlichiosis, and the primary care physician to be familiar babesiosis. I will conclude with an update on with the epidemiology of these diseases the most common of the tick-borne diseases, and their presentations. Although Lyme Lyme borreliosis. disease is the most common and well- • ROCKY MOUNTAIN SPOTTED FEVER known of the many tick-borne diseases, Rocky Mountain spotted fever, An acute febrile illness, Rocky Mountain ehrlichiosis, and babesiosis are also spotted fever is caused by Rickettsia rickettsii, a More threats throughout the United States. gram-negative intracellular bacillus transmit- Americans are ted by tick bites. The disease is misnamed: not S SUBURBS EXPAND and deer populations all patients develop rash, and fewer than 2% coming into 0continue to increase, more Americans of cases occur in Rocky Mountain states. contact with are coming into contact with rural problems Symptoms and course. The onset of such as tick-borne disease. Caused by symptoms begins 4 to 14 days after exposure tick-borne microorganisms endemic among white-tailed (mean, 7 days). Almost all patients have diseases deer, white-footed mice, or other mammals, fever. Headache, rash, or myalgia is experi- these diseases may be transmitted to humans enced by 80% or more of patients. Between through the bite of several species of ticks. one third and two thirds of patients experi- Identifying tick-borne diseases is difficult ence abdominal pain, nausea, or vomiting. for three reasons. First, tick-borne diseases However, the classic triad of fever, headache, often present with nonspecific symptoms that and rash is experienced by only about half of can be confused with a wide variety of unre- patients. The characteristic rash, which is not lated illnesses. Second, many patients never pruritic or painful, develops as macular lesions know that they have been bitten. Even though 3 to 5 days after the onset of the illness, pro- ticks may remain attached for hours or days, gressing to maculopapules and petechiae. they are tiny, their bites are painless, and they Starting on the wrists and ankles, it spreads to seek out hidden locations such as the axilla the palms and soles and then to the trunk. and the groin. Third, although serologic tests Between 9% and 16% of patients never expe- are available, they generally do not become rience a rash. In severe cases, patients may enter deliri- PATIENT INFORMATION um, shock, and renal failure. Mortality is # Avoiding tick bites, page 249 about 5%, being highest in older patients, CLEVELAND CLINIC JOURNAL OF MEDICINE VOLUME 67 • NUMBER 4 APRIL 2000 14 Downloaded from www.ccjm.org on September 25, 2021. For personal use only. All other uses require permission. men, blacks, and those who do not receive it difficult to diagnose. prompt treatment. The Ehrlichia organisms, members of the Epidemiology and demographics. Rocky Rickettsiaceae family, are gram-negative, Mountain spotted fever has been reported in intracellular pleomorphic bacilli. The disease 48 states of the United States, Mexico, and has two forms: human monocytic ehrlichiosis, Central and South America. About half of the found in the southeastern states, and human 600 American cases every year occur in North granulocytic ehrlichiosis, found in the Carolina, South Carolina, Tennessee, or Northeast, Midwest, and the West. The dis- Oklahoma. Although cases may occur at any eases, although clinically indistinguishable, time of year, about 90% of them occur arc caused by different organisms and carried between April and September during peak by different species of ticks, with white-tailed tick season. The age distribution of patients is deer and white-footed mice as reservoirs. bimodal, with most cases occurring among Symptoms and course. More than 60% of children age 5 to 9 years or among adults older those infected may be asymptomatic. than 60. The disease is somewhat more com- Symptoms, when they do develop, begin 7 to mon among men than women (1.7 to 1) and 14 days after exposure. Virtually all sympto- in whites than in blacks. Only about two matic patients have fever, and up to 85% have thirds of patients recall the tick bite. headache. Myalgia, malaise, and nausea are Differential diagnoses include measles, common. One third of patients with human meningococcemia, influenza, enterovirus, lep- monocytic ehrlichiosis and 2% to 11% of tospirosis, mononucleosis, viral hepatitis, those with human granulocytic ehrlichiosis typhoid fever, or idiopathic or thrombotic have a truncal rash, most commonly macu- thrombocytopenia purpura. Rocky Mountain lopapular, distinguishing it from Rocky spotted fever may also resemble another tick- Mountain spotted fever. The rash rarely affects borne disease, ehrlichiosis. the hands and feet. In fatal cases, an associa- Diagnosis should be made on the basis of tion has been noted with opportunistic infec- clinical symptoms and a careful patient histo- tions, leading to the possible conclusion that ry searching for any recent tick bites or out- ehrlichiosis may cause some degree of Serology door activity. Serologic tests can identify anti- immunosuppression. is used to bodies to the rickettsial organism, but only Severe disease may be characterized by after 7 to 10 days of infection; therefore, these seizures, coma, and renal, respiratory, and car- confirm, not tests are best used for confirmation after treat- diac failure, with mortality between 2% and diagnose, tick- ment has already begun. 10%. Laboratory tests are not particularly help- Characteristic laboratory findings are the borne disease ful. Although most patients become mildly combination of leukopenia, low platelet anemic, and some may have some thrombocy- counts, and elevated hepatic enzymes. About topenia, hyponatremia, or elevated liver half of patients become anemic. Blood sam- enzymes, these changes are not frequent ples from some patients will also have leuko- enough or severe enough to be diagnostic. An cytes with characteristic black spots called elevation in white blood cell counts at the morulae, intracellular cytoplasmic vacuoles beginning of the disease resolves quickly. occupied by Ehrlichia organisms. Treatment. Doxycycline is the preferred Epidemiology and demographics. Like treatment. It is also effective against ehrli- other tick-borne diseases, ehrlichiosis can chiosis, with which Rocky Mountain spotted occur at any time of year but is most common fever may be confused. Tetracycline may also between April and September. It is more com- be used. Chloramphenicol is recommended mon in men than women and is most frequent for children and pregnant women. between the ages of 43 and 60. About two thirds of patients recall being bitten by a tick. • EHRLICHIOSIS The tick must be attached for 24 to 48 hours to transmit the disease; therefore, daily tick Ehrlichiosis is an acute, febrile, multisystem checks can be an effective means of preven- disease with nonspecific symptoms that make tion. CLEVELAND CLINIC JOURNAL OF MEDICINE VOLUME 67 • NUMBER 4 APRIL 2000 245 Downloaded from www.ccjm.org on September 25, 2021. For personal use only. All other uses require permission. MEDICAL GRAND ROUNDS HHH FIGURE 1. Blood smear from a patient with FIGURE 2. Erythema migrans, the charac- babesiosis. Note the infected red blood teristic lesion that develops soon after cells bearing the characteristic ring forms being bitten by a tick infected with of Babesia microti (arrow). Borrelia burgdorferi, the causative agent of Lyme disease. Differential diagnosis. This disease may resemble Rocky Mountain spotted fever, range of the disease, but it appears to be most thrombotic thrombocytopenia purpura, hema- common in the Northeast, upper Midwest, tologic malignancy, hepatitis A, pneumonia, and West, with concentrations on Shelter, or viral diseases such as mononucleosis. Block, and Fire Islands in New York State. Diagnosis. Clinical findings, including Peak incidence occurs in June and July, but leukopenia and thrombocytopenia, with a the disease may occur from May to patient history of tick bite or possible tick September. The seroprevalence of babesiosis exposure, are important. Morulae are charac- in endemic areas is 9% to 21%, indicating teristic but do not occur in many patients and that many exposed to the disease are asymp- are difficult to recognize by the unsuspecting tomatic. It is more common among men The Lyme microscopist. Serologic testing can detect than women, and most common among disease antibodies to human monocytic ehrlichiosis those between ages 40 and 50. Fewer than after 2 to 3 weeks of infection. 10% of patients recall a tick bite. vaccine is not Treatment. Doxycycline is the treatment Differential diagnosis. The severe fever approved