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Cluster of Tick Paralysis Cases --- Colorado, 2006

Tick paralysis is a rare disease characterized by acute, ascending, flaccid paralysis that is often confused with other acute neurologic disorders or diseases (e.g., Guillain-Barré syndrome or botulism). Tick paralysis is thought to be caused by a toxin in tick saliva; the paralysis usually resolves within 24 hours after tick removal. During May 26--31, 2006, the Colorado Department of Public Health and Environment received reports of four recent cases of tick paralysis. The four patients lived (or had visited someone) within 20 miles of each other in the mountains of north central Colorado. This report summarizes the four cases and emphasizes the need to increase awareness of tick paralysis among health-care providers and persons in tick-infested areas.

Case 1. On May 15, a girl aged 6 years from Weld County awoke with symptoms of bilateral lower extremity weakness. She attended school as usual but needed assistance from a friend to walk outside for recess, where she fell down and was unable to get up. Her mother took her to an outpatient clinic, and a neurology appointment was arranged for the next day. She awoke the next day with a tingling sensation in her hands and feet, an inability to sit or stand on her own, and difficulty swallowing. She was taken to a local emergency department (ED) and transferred to a regional children's hospital. A physical examination revealed ophthalmoplegia (i.e., paralysis of muscles controlling eye movement), dysarthria (i.e., slurred or abnormal speech), and areflexia (i.e., absence of neurologic reflexes); nerve conduction studies indicated decreased velocities. The girl was admitted to the intensive-care unit on May 16 with a presumed diagnosis of Guillain-Barré syndrome and subsequently required intubation. On the evening of May 17, a nurse who was bathing the girl found a tick along her hairline. Investigators later learned that the tick had been visible on magnetic resonance imaging of the girl's head earlier that day. The tick was removed immediately, and the girl's symptoms improved; she was discharged home 1 week later. The tick was identified as a female Dermacentor andersoni. The girl often had visited her grandmother in the mountains in Larimer County and frequently hiked in the area. Seven days before symptom onset, the girl had visited her grandmother and played outside in the yard.

Case 2. On May 22, a man aged 86 years from the mountains in Larimer County began to have increased difficulty standing and transferring to and from his motorized scooter. The man was homebound as a result of chronic polyneuropathy and weakness from spinal stenosis. The next morning, his weakness worsened, and he was unable to walk or grasp objects. He called for emergency services and was admitted to the local hospital with a diagnosis of progressive worsening of his chronic neuropathy. Physical examination revealed normal cranial nerve function but generalized weakness; deep-tendon reflexes were absent. On the evening of May 23, a nurse who was changing the man's gown noticed a tick on his back. After tick removal, his symptoms improved during the next 4 days, and he was discharged home on May 27, although 2 weeks later he did not feel he had yet recovered to his baseline condition. The man did not report any recent travel or spending any time outdoors, with the exception of daily visits to his mailbox using his scooter. He owned a dog that was often outside, and he believed this was the likely source of the tick; the dog had no signs of tick paralysis.

Case 3. On May 22, a woman aged 78 years from the mountains in Grand County had generalized weakness and difficulty walking. During the next few days, her signs and symptoms progressed to facial weakness, slurred speech, decreased taste, and confusion. While the woman was preparing to go to the ED on May 25, her roommate noticed a tick on the back of the woman's neck below the hairline. Physical examination in the ED revealed normal cranial nerve function and no appreciable weakness, but the patient did have decreased deep-tendon reflexes. The ED physician removed the tick by cutting the surrounding tissue with a scalpel. The patient was discharged home to recover. The patient subsequently reported that within 24 hours her weakness, alteration in taste, and confusion were resolved; however, 3 weeks after discharge, she still became tired easily. The woman reported that she hiked or walked outside daily.

Case 4. A man aged 58 years from Larimer County with a history of chronic renal failure traveled to southern Texas on April 20. On April 24, he had a tingling sensation in his hands and perioral numbness. Three days later, he collapsed while trying to stand and was unable to get up. While helping him off the floor, his wife discovered a tick on the man's back. She removed the tick before transporting him to a local ED. He was transferred and admitted to an intensive-care unit but did not require intubation. Several hours later, he began to regain feeling in his hands and was able to walk with assistance. He was discharged home on May 5, but 6 weeks later he still reported residual subjective weakness. The patient reported that he frequently performed yard work and various outdoor recreational activities.

Reported by: WJ Pape, K Gershman, MD, Colorado Dept of Public Health and Environment. WM Bamberg, MD, EIS Officer, CDC.

Editorial Note:

The four cases described in this report illustrate the importance of considering tick paralysis in the differential diagnosis of persons with ascending paralysis who live in or visit tick-endemic regions. Diagnosis is confirmed by finding a tick embedded in the skin and observing for signs of improvement after tick removal; no other test exists for confirming tick paralysis. Although rare, cases of tick paralysis have been identified worldwide; most cases in North America occur in the western regions of Canada and the United States. The species most often associated with tick paralysis in the United States and Canada are the Rocky Mountain wood tick (D. andersoni) and the American dog tick (Dermacentor variabilis); however, 43 tick species have been implicated in human disease around the world (1). Most North American cases of tick paralysis occur during April--June, when adult Dermacentor ticks emerge from hibernation and actively seek hosts (2).

Tick paralysis is thought to be caused by a toxin secreted in tick saliva during feeding that reduces motor neuron action potentials and the action of acetylcholine, depending on the species of tick (1,3). Symptom onset usually occurs after 4--7 days of tick feeding. Ascending flaccid paralysis progresses over several hours or days; sensory loss does not usually occur, and pain is absent (4,5). Resolution of symptoms usually occurs within 24 hours of tick removal. When the tick is not removed, the mortality rate resulting from respiratory paralysis is approximately 10% (6,7).

Although tick paralysis is not a reportable disease in the state, the Colorado Department of Public Health and Environment receives, on average, a report of one case per year. The geographic and temporal clustering of cases described in this report is unusual. No explanation exists to account for this clustering; the risk for acquiring tick paralysis has been widespread in the western United States and Canada.

The cases described in this report also differ in other respects from previous reports. For example, the majority of patients have been children, particularly girls (2,7). However, in this cluster, only one patient was a child, and two patients were aged >70 years. The ticks removed from all four patients were on the neck or back; in previously reported tick paralysis cases, ticks were predominantly on the head and neck (7). Although outdoor exposure, such as hiking or camping in wooded areas, is usually associated with tick paralysis, one of the four patients was homebound with limited outdoor exposure.

Health-care workers discovered the ticks incidentally on two of the patients whose conditions had received alternative diagnoses. Health-care providers should consider a diagnosis of tick paralysis in any patient living in or visiting a tick-endemic area who has acute, symmetric paralysis and should perform a complete examination for ticks, particularly on the head, neck, and back. Ticks should be removed by grasping the tick close to the patient's skin with forceps and pulling with a steady, even pressure (8). Persons in tick-endemic areas should be educated regarding tick-borne diseases and should perform routine checks for ticks after possible exposures. Insect repellents should be applied to skin, and permethrin-containing acaricides should be sprayed on clothing to help prevent tick bites. Additional information regarding prevention of tick-borne diseases is available at


This report is based, in part, on contributions by S Rubaii, MD, Granby Medical Center, Granby; AC Nyquist, MD, The Children's Hospital, Denver; V Lambiase, Estes Park Medical Center, Estes Park; and R Grossmann, Larimer County Dept of Health and Environment, Fort Collins, Colorado.


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  4. Spach DH, Liles WC, Campbell GL, Quick RE, Anderson DE Jr, Fritsche TR. Tick-borne diseases in the United States. N Engl J Med 1993;329:936--47.
  5. McCue CM, Stone JB, Sutton LE. Tick paralysis: three cases of tick (Dermacentor variabilis Say) paralysis in Virginia: with a summary of all the cases reported in the Eastern United States. Pediatrics 1948;1:174--80.
  6. CDC. Tick paralysis---Wisconsin. MMWR 1981;30:217--8.
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  8. Needham GR. Evaluation of five popular methods for tick removal. Pediatrics 1985;75:997--1002.

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Date last reviewed: 8/30/2006


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