Asymptomatic Lyme Disease: A Ticking Time Bomb?

Is there a meaningful percentage of patients who contract Lyme disease but havenone of the early symptoms-neither the rash nor the flu-like symptoms (eg, fever,myalgia, headache, and stiff neck)-and in whom the disease only becomes clinicallyevident in a later stage when it is much harder to treat?

For example, if I tell patients who often walk in the woods to watch for a rashand/or flu-like symptoms (and to seek medical attention if any develop), will a smallpercentage of these patients present with a later stage of Lyme disease because theynever had any of the typical early symptoms? Similarly, if I advise patients who havebeen bitten by a tick that antibiotics are not needed unless a rash or flu-like symptomsoccur in the next 30 days, might some of these patients also present monthslater with serious, late-stage Lyme disease?
-Larry Novik, MD
  Bridgeport, Conn

In 2000, 17,730 cases of Lyme disease were reported inthe United States. The majority of cases were clusteredin southern New England, the eastern part of the MiddleAtlantic states, and the upper Midwest. There isalso a small endemic focus along the northern Pacificcoast.¹ The reported incidence of the disease is highest inyoung children between the ages of 5 and 10 years and inadults 50 to 59 years of age. Only a small percentage ofthese patients recall the tick bite.

Determining the risk of transmission. Several factorsaffect the risk of transmission of Borrelia burgdorferito man. The likelihood that a tick will be infected dependson the stage of the tick and on the region of the countryin which it is found. In endemic areas, 10% to 20% ofnymphal ticks and between 30% and 40% of adult ticks areinfected.² Additional studies have demonstrated that transmissiondoes not occur during the first 24 hours of attachment,and that an infected tick must remain attached to itshost for at least 48 hours for transmission to occur.¹ Keepin mind that these studies involved B burgdorferi; othertick-borne pathogens, such as Babesia and Ehrlichia, canbe transmitted earlier.

Magid and colleagues³ determined that the probabilityof contracting Lyme disease from a tick bite in an endemicarea ranges between 0.012 and 0.05. In 1996, datawere analyzed from 3 trials that involved a total of 600 patients.The rate of infection following a known tick bitewas 1.4%.⁴

Incidence of early symptoms. Erythema migrans-the skin lesion that signals infection with B burgdorferi-isreported in approximately 90% of patients who have Lymedisease.^5-7 When erythema migrans is present, the diagnosisis established and the patient is treated with an appropriatecourse of an antimicrobial agent.

Data from the Lyme vaccine trial by Steere andcoworkerss⁷ revealed a seroconversion rate of 0.028% in patientswith no symptoms, while seroconversion was documentedin 0.60% of those with a flu-like illness.

In general, Lyme disease subsequently develops invery few completely asymptomatic patients (less than 1%);a more likely scenario is that these patients had earlysymptoms but were not aware of them.

Weighing the treatment options. The pros andcons of 3 approaches to patients with known tick biteswere delineated in guidelines from the InfectiousDiseases Society of America.⁸ Treating all patients wouldexpose them to the risk of an adverse reaction to the antibiotic.If one treated only patients to whom a tick hadbeen attached for at least 48 hours, one would neglectpatients who had been exposed to other tick-bornepathogens that do not require 48 hours of attachment forinfection to be transmitted. Thus, routine use of antibioticsin persons who have sustained a tick bite is not recommended.Only individuals in highly endemic areaswho have been bitten by engorged nymphal ticks shouldbe given antimicrobial prophylaxis. Following a doubleblind,placebo-controlled trial that involved 482 patients,Nadelman and colleagues⁹ concluded that a single200-mg dose of doxycycline can prevent infection withB burgdorferi if administered within the first 72 hours followinga tick bite.

Each case must be considered individually. Factorsto be weighed include the degree of endemicity ofthe region, the stage of the tick, and the duration of attachment.Complications, adverse effects, and relativecontraindications of antimicrobial agents must also be reviewedand a risk-to-benefit analysis applied for eachpatient.

In most instances, patients with known tick bitesshould be monitored for signs and symptoms-rash andfever-for 30 days following exposure. If a patient is highlyapprehensive about contracting Lyme disease, considerordering acute and convalescent serologies.

Prevention. As with all infectious disease, the primarygoal is to prevent infection. Educate patients abouttick habitats, and caution them to avoid these areas when possible. Instruct patients with occupationalexposure to apply insectrepellent to their clothing. Counselall patients in endemic areas to examinethemselves for ticks after beingoutdoors. These measures are paramountin controlling the transmissionof B burgdorferi and eliminating the overuse of antimicrobialagents.
-Susan Conaty, PA-C
  State University of New York
  Stony Brook

-Raymond Dattwyler, MD
  Professor of Medicine
  Director, Lyme Disease Center
  State University of New York
  Stony Brook

References:

REFERENCES:1. Centers for Disease Control and Prevention. Lyme disease-United States,2000. MMWR. 2000;51:29.
2. Rauter C, Oehme R, Diterich I, et al. Distribution of clinically relevantBorrelia genospecies in ticks assessed by a novel, single-run, real-time PCR.J Clin Microbiol. 2002;40:36-43.
3. Magid D, Schwartz B, Craft J, Schwartz JS. Prevention of Lyme disease aftertick bites. A cost-effectiveness analysis. N Engl J Med. 1992;327:534-554.
4. Warshafsky S, Nowakowski J, Nadelman RB, et al. Efficacy of antibiotic prophylaxisfor prevention of Lyme disease. J Gen Intern Med. 1996;11:329-333.
5. Shapiro E, Gerber M. Lyme disease. Clin Infect Dis. 2000;31:746-747.6. Sigal LH, Zahradnik JM, Lavin P, et al. A vaccine consisting of recombinantBorrelia burgdorferi outer surface protein A to prevent Lyme disease. N Engl JMed. 1998;339:216-222.
7. Steere AC, Sikand VK, Meurice F, et al. Vaccination against Lyme disease withrecombinant Borrelia burgdorferi outer-surface lipoprotein A. Recombinant Outer-Surface Protein A Lyme Disease Vaccine Study Consortium. N Engl J Med. 1998;339:209-215.
8. Wormser GP, Nadelman RB, Dattwyler RJ, et al. Practice guidelines for thetreatment of Lyme disease. The Infectious Diseases Society of America. ClinInfect Dis. 2000;31(suppl 1):S1-S14.
9. Nadelman RB, Nowakowski J, Fish D, et al. Prophylaxis with single dosedoxycycline for the prevention of Lyme disease after Ixodes scapularis tick bite.N Engl J Med. 2001;345:79-84.