Pediatrics

Tick paralysis

OVERVIEW: What every practitioner needs to know

Tick paralysis (TP), a uniquely tick-borne poisoning, is an ascending flaccid neuromuscular paralysis with sensory sparing caused by salivary neurotoxins secreted by gravid hard ticks (Acari: Ixodidae) while blood-feeding. Although reported worldwide since 1912 and transmitted by 43 tick species, TP usually occurs in the same regions of North America and Australia during predictable spring-summer tick-breeding seasons.

North American TP is most commonly transmitted by Dermacentorandersoni, the Rocky Mountain wood tick, in the US Pacific Northwest, US West, and Southwestern Canada (British Columbia, Alberta (Figure 1).

Figure 1.

Dermacentor andersoni, the Rocky Mountain wood tick

In the Southeast US, TP is usually transmitted by Dermacentorvariabilis, the American dog tick (Figure 2).

Figure 2.

Dermacentor variabilis, the American dog tick

In Eastern Australia, TP is usually transmitted by Ixodes holocyclus, the marsupial or paralysis tick, especially along the Australian Gold Coast of Southeast Queensland.

Are you sure your patient has tick paralysis? What are the typical findings for this disease?

North American TP is characterized by a distinct prodrome that begins some time after a gravid ixodid tick bite and secretion of an unidentified salivary neurotoxin, and comprises 2 distinct phases including:

(1) a nonspecific prodromal phase of lethargy and weakness; and

(2) a subsequent neurotoxic phase of acute ataxia (often described as an inability to sit up and to walk without assistance), progressing to ascending flaccid paralysis with preserved sensorium.

Unlike Australian TP, the recovery time to normal neurological function in North American TP is rapid and occurs within 1.5 days of tick removal (Table I).

Table I.

An Epidemiological, Clinical, and Neurophysiological Comparison of North American and Australian Tick Paralysis
Regional Tick Paralysis (TP) North American Tick Paralysis (TP) Australian Tick Paralysis (TP)
Geographic distribution Southwest Canada (British Columbia, Alberta)United States (US) Pacific Northwest and Rocky Mountain WestUS Southeast Atlantic and Gulf of Mexico Coasts. Eastern Australia: Southeast Queensland and New South Wales.
Incidence(N.B. The true annual US incidence is unknown.) Rare. Colorado reports one case per year. May occur in clusters. Rare in humans, more common in animals, especially dogs.
Seasonality Spring-summer Spring-summer
Preferred tick vectors Canada and US Northwest and West: Dermacentor andersoni (Rocky Mountain wood tick)US Southeast: Dermacentor variabilis (American dog tick)Other gravid female ixodid ticks may also rarely transmit TP in the US. Ixodes holocyclus (marsupial or paralysis tick)2 other gravid female Ixodes spp. may rarely transmit TP in Australia.
Other potential tick vectors Amblyomma americanum (Lone Star tick), Amblyomma maculatum (Gulf Coast tick), Ixodespacificus (Western black-legged or Western wood tick) Ixodes cornuatus (one human case reported), Ixodes hirsti (only animal cases reported to date)
Preferred tick attachment sites Scalp, often behind the ears. Scalp, often behind the ears.
Neurotoxins Neurotoxin produced by gravid female ixodid ticks and concentrated in salivary glands; not fully characterized at present; not botulinum-like. Neurotoxin produced by gravid female ixodid ticks and concentrated in salivary glands; not fully characterized at present; botulinum-like.
Age predilections Children, ages 1-8 years. May occur in adults much less commonly. Children, ages 1-5 years. May occur in adults much less commonly.
Sex predilections Females < 8 years old. Children < 5 years old.
Prodromes Present, short duration (24 hours): no to low-grade fever, irritability, fatigue, weakness, muscle pain & paresthesias. Present, longer duration (48-72 hours): afebrile, fatigue, sleepiness-drowsiness, weakness, leg pain, unsteady gait.
Fever Rare, but may be low grade during prodrome. Rare, but may be low grade during prodrome. Fever occurs commonly following canine antitoxin administration.
Exanthem Rare, prodromal pruritic papular rash possible. Absent. Urticarial rashes are common following antitoxin administration.
Incubation periods (days) Short, 1-1.5 days Longer, 3-5 days
Paralysis onset (hours) Within 24 hours of tick attachment. Later, within 48-72 hours of tick attachment.
Maximum intensity of paralysis (hours) Within 24-48 hours if tick is not removed. Worsens to maximum intensity 48 hours after tick removal.
Tick bite site eschars Absent Absent
Regional lymphadenopathy Absent Absent
Cranial nerve involvement Present later: drooling, dysphagia, dysphonia, facial weakness. Facial nerve palsies more common than internal and external ophthalmoplegia. Present early: internal & external ophthalmoplegia common.
Cerebrospinal fluid (CSF) analysis Normal. Normal.
Treatment Tick removal. Tick removal.Temporary mechanical ventilation may be indicated, especially in children.Canine antitoxin recommended (serum sickness common). Antipyretics and antihistamines are recommended for fever & urticarial rashes following antitoxin administration.
Neurological recovery time (days) Rapid, 1-1.5 days. Prolonged, 1-3+ weeks.
Nerve conduction studies Reduced amplitude of compound muscle action potentials (CMAPs).Normal sensory nerve action potentials (SNAPs).Normal response to repetitive nerve stimulation.Decreased nerve conduction velocities.Prolonged distal motor nerve latencies. Reduced amplitude of CMAPs.Normal SNAPs.Normal response to repetitive nerve stimulation.
Case fatality rates(without tick removal) Canada: 10%-12% (before 1954).US: 6%-10% (1940s-Present, deaths occurred in the 1940s). Unknown. 20 deaths were reported from TP in New South Wales, Australia, over the period, 1900-1945.

What other disease/condition shares some of these symptoms?

A bedside clinical differential diagnosis of acute ascending flaccid paralysis with a preserved sensorium is relatively narrow and should include TP, Guillain-Barré syndrome, spinal cord tumor, botulism, and poliomyelitis (Table II).

Table II.

The Clinical Differential Diagnosis of Tick Paralysis (TP) versus Neuromuscular Paralysis with Preserved Sensorium
Presenting ClinicalFeatures Tick Paralysis (TP) Guillain-Barré Syndrome Cervical Spinal Cord Lesion Botulism Poliomyelitis
Onset of neuromuscular paralysis Acute, rapid, within 24-48 hours of tick attachment in North American TP; longer onset, 48-72 hours, in Australian TP. Slower onset, days to weeks. Abrupt to gradual onset. Gradual and often following acute gastrointestinal prodrome of nausea, vomiting, diarrhea.Recent history of ingestion of unpasteurized honey, home-canned or pickled foods and salad dressings may be present. Gradual onset, following a prodrome of fever, meningeal signs, and asymmetrical weakness.
Direction of neuromuscular paralysis Ascending Ascending Ascending Descending Ascending
Ataxia Present Absent Absent Absent Absent
Deep tendon reflexes Hyporeflexia progressing to areflexia Hyporeflexia progressing to areflexia Variable Variable Hyporeflexia progressing to areflexia
Babinski sign Absent Absent Present Absent Absent
Sensory loss None Mild Present Absent Absent
Meningeal signs Absent Rarely present Absent Absent Present
Ophthalmoplegia (external & internal) May be present in North American TP.Often present and pathognomonic of Australian TP. Absent Absent Often present & also pathognomonic. Absent
Other cranial nerve palsies Present May be present Absent Present Absent
Fever Low grade, if present. Often follows antitoxin administration in Australian TP. Rarely present Absent Often present Present
Exanthem May be present. Urticarial rashes often present following antitoxin administration in Australian TP. Absent Absent Absent Absent
CSF findings:Protein levels (mg/dL)White cells per mm3Differentialcounts Normal< 10 Normal High (≥ 40) < 10< 10 mononuclear cells/mm3 Normal to high Variable Normal Normal < 10Polymorphonuclear leukocytosis possible High (≥ 40) >10 Lymphocytosis possible
Nerve conduction studies ↓ amplitude of compound muscle action potentials (CMAPs).Normal sensory nerve action potentials (SNAPs).Normal response to repetitive nerve stimulation.↓ nerve conduction velocities.Prolonged distal motor nerve latencies. Similar Similar Similar with a reduction in compound muscle nerve action potentials(CMAPs). However, with exercise or following rapid, repetitive stimulation, the amplitude of CMAPs may be further reduced. Similar
Time to neurologic recovery (hours) Rapid, ≤ 24 hours after tick removal in north American TP; more prolonged, 48-72 hours, in Australian TP. Weeks to months Variable Prolonged Prolonged
Permanent neurologic deficits None after tick removal in North American TP; prolonged weakness possible in Australian TP. Permanent paresis possible Permanent paresis possible Permanent paresis possible & frequent Permanent paresis common

Botulism causes a descending neuromuscular paralysis with a preserved sensorium and ophthalmoplegia; and poliomyelitis has been nearly eradicated by vaccination worldwide. However, poliomyelitis may occur in unvaccinated patients with positive travel histories to polio-endemic regions of the world or following vaccination with live oral polio virus vaccines (OPV).

Since TP and Guillain-Barré syndrome both have identical electrophysiological signatures on nerve conduction testing, the only way to differentiate the diseases is to find and remove an attached, blood-feeding tick and observe the rapidity of neurological recovery. Postmortem examinations of persons who have died suddenly of unexplained paralytic illnesses have demonstrated attached ticks on the head and neck of decedents.

What caused this disease to develop at this time?

The US and Canadian Pacific Northwest Coasts, the US Southeast Atlantic and Gulf Coasts, and the Australian Gold Coast of Southeast Queensland are among the most popular and scenic destination resorts in the world today. Vacation travelers to such TP-endemic regions may return home with TP, as reported in 2003 by Inokuma and co-authors in a Japanese traveler returning from vacation on the Gold Coast of Australia.

In the American Pacific Northwest, most cases of TP occur during April through June when Dermacentor ticks emerge from hibernation to mate and to seek blood meals. In addition, most cases of TP in North America have occurred sporadically in young girls with long hair and believed to be predisposed to unnoticed ticks blood-feeding on the scalp or nape of the neck. However, a 4-patient cluster of TP, including a 6-year-old girl with a tick on her hairline and 3 adults with ticks on the neck and back, were reported by the US Centers for Disease Control and Prevention in Colorado in 2006.

Although children, especially girls younger than 8 years of age, are most commonly afflicted with TP, boys and adults may also be affected and often present with ticks attached at sites other than the head and scalp.

What laboratory studies should you request to help confirm the diagnosis? How should you interpret the results?

With the exception of nerve conduction studies, diagnostic laboratory and radiologic imaging studies will be normal in TP (Table I). The results of nerve conduction studies will be similar to several other conditions that may result in neuromuscular paralysis with a preserved sensorium (Table II).

Would imaging studies be helpful? If so, which ones?

Although there is no intracranial pathology in TP, and neuroimaging studies of the head and brain are usually interpreted as normal, there have been cases of TP in which magnetic resonance images of the head have disclosed blood-feeding ticks concealed by scalp hair and have directed the only effective treatment by proper tick removal.

Confirming the diagnosis

Today, more cases of TP in children in the US are being misdiagnosed and treated as Guillain-Barré syndrome (GBS), especially in children, before conducting careful body searches for ticks at preferred attachment sites.

Diaz analyzed 50 cases of TP over the study period 1946-2006, and reported that TP occurred seasonally and sporadically in individuals and in clusters of children and adults of both sexes in urban and rural locations, with a case fatality rate of 6.0% over 60 years. The proportion of misdiagnoses of TP as GBS was significantly greater (p = 0.005) in more recently collected series of TP cases, 1992-2006, than the proportion of misdiagnoses in earlier series, 1946-1996.

Such misdiagnoses often directed unnecessary therapies such as central venous plasmapheresis with intravenous gammaglobulin G (IVIG), and often delayed correct diagnosis and tick removal.

If you are able to confirm that the patient has tick paralysis, what treatment should be initiated?

Most patients with TP do not recall painless tick bites, and attachment sites may be unseen or hidden by long hair. Nevertheless, tick localization and removal as soon as possible, preferably within 24 hours, remain recommended strategies to reverse TP. Ticks should always be removed with forceps (or tweezers), not fingers (as squishing ticks can transmit several tick-borne microbial diseases across dermal barriers or create infectious aerosols), and in contiguity with their feeding mouthparts, rather than burning ticks with spent matches, or painting embedded ticks with adhesives or nail polishes (Figure 3).

Figure 3.

Initiate tick removal by grasping attached tick across the cephalothorax with forceps or tweezers.

Ticks should be removed with forceps or fine-tipped tweezers applied close to the point of skin attachment with gentle, steady traction applied to avoid decapitating ticks and leaving imbedded mouthparts with toxin-filled salivary glands (Figure 4).

Figure 4.

Complete tick removal by applying steady, non-twisting traction perpendicular to attachment site.

What are the adverse effects associated with each treatment option?

Improper tick removal may decapitate the tick and leave imbedded mouthparts with toxin-filled salivary glands in place with continuing neuromuscular paralysis. Although I. holocyclus TP in Australia is also treated by proper tick removal, transient neuromuscular deterioration may occur for 24-72 hours following tick removal, with a peak paralysis often at 48 hours after tick removal. Therefore, respiratory monitoring in an ICU is recommended in cases of Australian TP for 72 hours following proper tick removal.

What are the possible outcomes of tick paralysis?

Further investigations of TP, especially cases of TP in returning vacationers and in adults and children that are misdiagnosed and treated (often by plasmapheresis with IVIG) as GBS or other inflammatory ascending polyneuropathies, are recommended. TP should be added to and excluded from the differential diagnoses of acute ataxia and ascending flaccid paralysis in adults and children visiting and returning home from the TP-endemic regions of the US, Canada, and Australia in order to curtail a highly significant trend towards the misdiagnosis of TP as GBS and to delay the immediate management of TP by prompt tick removal.

What causes this disease and how frequent is it?

Tick paralysis (TP) is only transmitted by blood-feeding gravid adult female ticks of several species, but most commonly by ixodid or hard ticks. During blood-feeding, the tick will inject incompletely characterized neurotoxins produced by the tick's salivary glands into the bite wound along with anticoagulant and anesthetic chemicals. TP is an infrequent disorder, with Colorado reporting the highest incidence rate of 1 case per year. During a 60-year period in the US, 50 well-documented cases of TP were reported, mostly from the US Pacific Northwest, but also from the Southeast US.

The emergence of Lyme disease (LD) in the United States in the early 1970s, whose causative agent, the spirochete Borrelia burgdorferi, was not identified until 1982, sparked renewed interest in tick-borne diseases worldwide. By the early 1990s, LD had become the most common arthropod-borne infectious disease in the US and Europe.

Today, many other tick-borne infectious diseases, especially the rickettsial diseases, are re-emerging worldwide with unanticipated tick vectors and greater pathogenicity. Climate changes, especially global warming with milder winters, and human lifestyles and leisure activities, now place humans and ticks together outdoors for longer periods for tick breeding, blood-feeding, and disease transmission.

How do these pathogens/genes/exposures cause the disease?

The exact mechanism of ascending neurotoxic paralysis in North American Dermacentor tick-transmitted TP is unknown, but neuroelectrophysiological studies have demonstrated blockage of sodium flux across axonal membranes at the nodes of Ranvier. In Australia, the marsupial ixodid tick, Ixodes holocyclus, can cause a more severe and delayed onset ascending paralysis by producing a salivary neurotoxin that blocks neuromuscular transmission by blocking the presynaptic release of acetylcholine. (See Table II.)

What complications might you expect from the disease or treatment of the disease?

The major complication from TP is hypoventilation and respiratory failure from ascending neuromuscular paralysis as a result of either misdiagnosis or delayed diagnosis. The major complications from the treatment of TP by tick removal (Figure 3 and Figure 4) are incomplete removal of the tick's feeding mouthparts and re-paralysis within 48-72 hours of proper tick removal in cases of Australian TP transmitted by the marsupial tick.

Are additional laboratory studies available; even some that are not widely available?

Although most diagnostic laboratory and radiographic studies are negative in TP, nerve conduction studies will assist clinicians in limiting the differential diagnosis of ascending neuromuscular paralysis (Table II).

How can tick paralysis be prevented?

Effective strategies for the prevention and control of TP include personal protective measures, landscape management, and wildlife management.

Personal protective measures to prevent TP include wearing appropriate clothing, applying insect repellants to clothing and exposed skin, and performing regular tick-checks. Wearing long pants tucked into socks, long-sleeved shirts, and light-colored clothing can help keep ticks off the skin and make them easier to spot on clothing. Spraying and/or impregnating clothing with pyrethrin/pyrethroid-containing insecticides (permethrin, deltamethrin, etc.) are highly effective repellant strategies against ticks and other insects. The topical application of insect repellants containing 10%-50% formulations of N, N-diethyl-meta-toluamide (DEET) or 20% picaridin (only available in the US as a 7% formulation) directly on exposed skin is another effective and recommended measure while outdoors in tick-infested areas, with less concentrated formulations of DEET (≤ 20%-30%) recommended for children.

Landscape management strategies to prevent tick-borne diseases include widespread application of acaricides over tick -preferred ecosystems, removal of vegetation and leaf litter near homes and recreation sites, and creation of dry barriers of gravel, stone, rocks, shredded rubber, or wood chips between forested areas and yards or playgrounds.

Domestic and wild animal management strategies to prevent tick-borne diseases include encouraging the development of better veterinary vaccines and topical pesticides for tick-borne diseases in large domestic and wild animal reservoirs; applying the safest acaricides actively and routinely to domestic animals and passively to wild animals. Deer and cattle can be humanely treated at baited feeding or watering stations, tick dips, and salt licks. Effective rodent control measures may include setting out rodenticide-baited rodent houses for rodents to occupy or acaricide-baited cotton, lint, or fabric balls for rodents to adopt as nesting materials, especially in crawl spaces under homes and near playgrounds, to control several rodent infectious disease-transmitting ectoparasites, including ticks, mites, and fleas.

What is the evidence?

Dworkin, MS, Shoemaker, PC, Anderson, DE. "Tick paralysis: 33 human cases in Washington state, 1946-1996". Clin Infect Dis. vol. 29. 1999. pp. 1435-9.

Greenstein, P. "Tick paralysis". Med Clin North Am. vol. 86. 2002. pp. 441-6.

Felz, MW, Smith, CD, Swift, TR. "A six-year-old girl with tick paralysis". N Engl J Med. vol. 342. 2000. pp. 90-4.

Schaumburg, HH, Herskovitz, S. "The weak child--a cautionary tale". N Engl J Med. vol. 342. 2000. pp. 127-9.

Inokuma, H, Takahata, H, Fournier, PE. "The paralysis by Ixodes holocylus in a Japanese traveler returning from Australia". Ann N Y Acad Sci. vol. 990. 2003. pp. 357-8.

Vedanarayanan, VV, Evans, OB, Subramony, SH. "Tick paralysis in children: electrophysiology and possibility of misdiagnosis". Neurology. vol. 59. 2002. pp. 1088-90.

"Cluster of tick paralysis--Colorado, 2006". MMWR Morb Mortal Wkly Rep. vol. 55. 2006. pp. 933-5.

Diaz, JH. "A 60-year meta-analysis of tick paralysis in the United States: a predictable, preventable, and often misdiagnosed poisoning". J Med Toxicol. vol. 6. 2010. pp. 15-21.

Ongoing controversies regarding etiology, diagnosis, treatment

Further investigations of TP, especially cases of TP in returning vacationers and in adults and children who are misdiagnosed and treated (often by plasmapheresis with IVIG) as GBS or other inflammatory ascending polyneuropathies, are recommended. TP should be added to and excluded from the differential diagnoses of acute ataxia and ascending flaccid paralysis in adults and children visiting and returning home from the TP-endemic regions of the US, Canada, and Australia in order to curtail a highly significant trend towards the misdiagnosis of TP as GBS and to delay the immediate management of TP by prompt tick removal.

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