Faculty peer reviewed
A healthy 42-year old patient presents to your office after a day of hiking with his family in Upstate New York. This morning in the shower he found a “big black tick” on his right leg. He is currently asymptomatic and wants to know what his risk of Lyme disease is.
For New York City physicians, the end of summer and beginning of fall herald a spike in cases of Lyme Disease. Each year in the United States, over 19,000 patients are diagnosed with Lyme Disease; 93% of cases occur in just 10 states, among them New York, and its neighbors, Connecticut and New Jersey.(1) When there are four hundred New York City residents presenting with this illness every year, what’s a physician to do when patients are worried that they are about to become a statistic? (2) In the following article, we discuss the diagnostic and therapeutic approaches to a patient who reports being bitten by a tick.
Lyme disease is a tick-borne illness caused by the spirochete Borrelia burgdorferi. It is transmitted to humans by the bite of several species of tick from the genus Ixodes. These ticks go through several stages in their life cycle: egg, larva, nymph, and adult. Borrelia is usually carried by those parasites in the nymph stage, inhabiting the lumen of the insect’s gut. Once a blood meal enters the gut, Borrelia reproduces and migrates to the salivary glands of the insect, where it can be transmitted to a new host. This process creates a time lag in between the tick attachment to the host and the transmission of Lyme disease. Prospective studies of patients bitten by Ixodes confirm the clinical significance of this incubation: Lyme disease is rarely transmitted from tick to human host without at least 72 hours of feeding.(3,4)
Proper removal technique
A successful tick removal will completely remove all tick body parts without releasing infectious material and/or inducing the tick to salivate. While multiple methods of tick removal have been documented in the literature, including several commercial products, the most commonly recommended method is via manual extraction.(5,6) Using blunt forceps, the tick should be grasped as close to the skin as possible and pulled up without crushing any tick body parts. Following the successful removal, the surrounding skin should be thoroughly disinfected.
Possibility of Prophylaxis
While many patients will likely request antibiotics following a tick bite, recent guidelines from the Infectious Diseases Society of America recommend prophylaxis as an option only for certain patients.(7) Patients can be given doxycycline if all of the following criteria are met:
(1) The tick must be identified as a member of the Ixodes genus. Nymphal Ixodes ticks are tiny and round without spots. A good chart for differentiating the common North American ticks can be found at the CDC’s Division of Vector-Borne Infectious Diseases at http://www.cdc.gov/ncidod/dvbid/lyme/ld_blackleggedTick.htm.
(2) The tick is estimated to have been attached for at least 36 hours. This can be calculated based either on the most likely time of exposure or clinician evaluation of the level of tick engorgement.
(3) Infection occurred in area with a high level of Borrelia infection of the ticks (>20%). This can be assumed for most areas in New York, New Jersey, and Connecticut.
(4) The patient presents within 72 hours of removing the tick.
(5) Doxycycline is not otherwise contraindicated, as in the case of pregnant women and children under 8 years of age.
For patients who do not meet the above requirements, a watchful waiting strategy is recommended. The patient should be instructed to regularly inspect the site of the bite for 30 days and alert the physician of any changes in their health.
Signs of Infection
Less than four percent of patients who are bitten by ticks develop signs of Lyme disease.(4) Given the severity of undiagnosed late stage disease, timely identification of infected patients is vital. The targetoid rash, erythema migrans, occurs at the site of microbe entry and is characteristic of an early localized response to infection with Borrelia.(8) Diagnosis of Lyme disease can be made based on the presence of erythema migrans. Antibiotic therapy should be started immediately. A small portion of Lyme disease patients will develop early disseminated disease without ever documenting signs of the characteristic rash.(8) It is important to be vigilant regarding the onset of acute neurologic (cranial neuropathy, peripheral neuropathy or meningitis) or cardiac (myocarditis or atrioventricular block) symptoms. In both cases, the diagnosis of Lyme disease can be made purely based on clinical symptoms. Serologic testing should not be part of a first-line diagnostic work-up.
The literature supports the use of doxycycline, amoxicillin, or cefuroxime for early local infections.(7) Of these three, doxycycline is often used because of its coverage of a potential co-infecting microbe, Anaplasma phagocytophilum, which causes human granulocytic anaplasmosis. In the case of early disseminated disease, 14 days of intravenous therapy with ceftriaxone and cefotaxime is recommended.vii If the patient presents with symptomatic heart disease, hospitalization for cardiac monitoring may be required.
An attached but unengorged tick is found on the right thigh of your hiking patient and removed intact appropriately with blunt forceps. Given that the tick was likely attached for less than 24 hours, the patient does not require prophylaxis. He is educated about tick safety and sent home with instructions to report the appearance of a rash or any changes in his health.
Joshua Allen-Dicker is a 4th year medical student at NYU School of Medicine.
Faculty peer reviewed by Harold Horowitz MD, Professor of Medicine (Infectious Diseases and Immunology)
1) Bacon. MR, Kugeler, KJ, Mead PS. Surveillance for Lyme Disease: United States, 1992-2006. MMWR. 2008;57(SS10):1-9.
2) Lyme Disease. Bureau of Communicable Diseases New York City Department of Health and Mental Hygiene. http://www.nyc.gov/html/doh/html/cd/cdlym.shtml. Accessed July 27, 2009.
3) Sood SK; Salzman MB; Johnson BJ et al. Duration of tick attachment as a predictor of the risk of Lyme disease in an area in which Lyme disease is endemic. J Infect Dis 1997 Apr;175(4):996-9.
4) Nadelman RB, Nowakowski J, Fish D et al. Prophylaxis with single-dose doxycycline for the prevention of Lyme disease after an Ixodes scapularis tick bite. N Engl J Med 2001 Jul 12;345(2):79-84.
5) Oteo JA, Martinez de Artola V, Gomez-Cadinanos R, et al. Evaluation of methods of tick removal in human ixodidiasis. Rev Clin Esp 1996;196:584-7.
6) Gammons, M and Salam, G. Tick Removal. Am Fam Physician 2002;66:643-5.
7) Wormser GP et al. The Clinical Assessment, Treatment, and Prevention of Lyme Disease, Human Granulocytic Anaplasmosis, and Babesiosis: Clinical Practice Guidelines by the Infectious Diseases Society of America. Clin Infect Dis. 2006;43(9):1089-1134.
8 ) Steere, AC, Sikand, VK. The presenting manifestations of Lyme disease and the outcomes of treatment. N Engl J Med 2003; 348:2472.