Tick paralysis
Encyclopedia
Tick paralysis is the only tick-borne disease
that is not caused by an infectious organism. The illness is caused by a neurotoxin
produced in the tick
's salivary gland
. After prolonged attachment, the engorged tick transmits the toxin to its host. The incidence of tick paralysis is unknown.
s within 2–7 days, beginning with weakness in both legs that progresses to paralysis
. The paralysis ascends
to the trunk, arms, and head within hours and may lead to respiratory failure and death. The disease can present as acute ataxia
without muscle weakness.
Patients may report minor sensory symptoms, but constitutional signs are usually absent. Deep tendon reflexes are usually hypoactive or absent, and ophthalmoplegia and bulbar palsy
can occur.
Electromyographic
(EMG) studies usually show a variable reduction in the amplitude of compound muscle action potential
s, but no abnormalities of repetitive nerve stimulation studies. These appear to result from a failure of acetylcholine release at the motor nerve terminal level. There may be subtle abnormalities of motor nerve
conduction velocity and sensory action potentials.
) and the American dog tick (Dermacentor variabilis
); however, 43 tick species have been implicated in human disease around the world. Most North American cases of tick paralysis occur from April to June, when adult Dermacentor ticks emerge from hibernation and actively seek hosts. In Australia, tick paralysis is caused by the tick Ixodes holocyclus. Prior to 1989, 20 fatal cases were reported in Australia.
Tick paralysis has killed thousands of animals, mainly cows and sheep, in other parts of the world. Although tick paralysis is of concern in domestic animals and livestock in the United States as well, human cases are rare and usually occur in children under the age of 10.
Tick paralysis occurs when an engorged and gravid (egg-laden) female tick produces a neurotoxin
in its salivary glands and transmits it to its host during feeding. Experiments have indicated that the greatest amount of toxin is produced between the fifth and seventh day of attachment (often initiating or increasing the severity of symptoms), although the timing may vary depending on the species of tick.
Unlike Lyme disease
, ehrlichiosis
, and babesiosis
, which are caused by the systemic proliferation and expansion of parasites in their hosts long after the offending tick is gone, tick paralysis is chemically induced by the tick and therefore usually only continues in its presence. Once the tick is removed, symptoms usually diminish rapidly. However, in some cases, profound paralysis can develop and even become fatal before anyone becomes aware of a tick's presence.
In the absence of a tick, the differential diagnosis includes Guillain-Barre syndrome
.
is currently available for any tick-borne disease, except for Tick-borne encephalitis. Individuals should therefore take precautions when entering tick-infested areas, particularly in the spring and summer months. Preventive measures include avoiding trails that are overgrown with bushy vegetation, wearing light-coloured clothes that allow one to see the ticks more easily, and wearing long pants and closed-toe shoes. Tick repellents containing DEET
(N,N, diethyl-m-toluamide) are only marginally effective and can be applied to skin or clothing. Rarely, severe reactions can occur in some people who use DEET-containing products. Young children may be especially vulnerable to these adverse effects. Permethrin
, which can only be applied to clothing, is much more effective in preventing tick bites. Permethrin is not a repellent but rather an insecticide; it causes ticks to curl up and fall off the protected clothing.
since the first isolation in 1966, the exact structure of the toxin is still unknown. The 40-80 kDa protein
fraction contains the toxin.
Tick-borne disease
Tick-borne diseases are diseases or illnesses transmitted by ticks. As the incidence of tick-borne illnesses increases and the geographic areas in which they are found expand, it becomes increasingly important that health professionals be able to distinguish the diverse, and often overlapping,...
that is not caused by an infectious organism. The illness is caused by a neurotoxin
Neurotoxin
A neurotoxin is a toxin that acts specifically on nerve cells , usually by interacting with membrane proteins such as ion channels. Some sources are more general, and define the effect of neurotoxins as occurring at nerve tissue...
produced in the tick
Tick
Ticks are small arachnids in the order Ixodida, along with mites, constitute the subclass Acarina. Ticks are ectoparasites , living by hematophagy on the blood of mammals, birds, and sometimes reptiles and amphibians...
's salivary gland
Salivary gland
The salivary glands in mammals are exocrine glands, glands with ducts, that produce saliva. They also secrete amylase, an enzyme that breaks down starch into maltose...
. After prolonged attachment, the engorged tick transmits the toxin to its host. The incidence of tick paralysis is unknown.
Signs and symptoms
Tick paralysis results from inoculation of a toxin from tick salivary glands during a blood meal. The toxin causes symptomSymptom
A symptom is a departure from normal function or feeling which is noticed by a patient, indicating the presence of disease or abnormality...
s within 2–7 days, beginning with weakness in both legs that progresses to paralysis
Paralysis
Paralysis is loss of muscle function for one or more muscles. Paralysis can be accompanied by a loss of feeling in the affected area if there is sensory damage as well as motor. A study conducted by the Christopher & Dana Reeve Foundation, suggests that about 1 in 50 people have been diagnosed...
. The paralysis ascends
Ascending paralysis
Ascending paralysis refers to a form of paralysis where the presentation appears in the lower limbs before the upper limbs.It can be associated with:* Guillain–Barré syndrome *Tick paralysis...
to the trunk, arms, and head within hours and may lead to respiratory failure and death. The disease can present as acute ataxia
Ataxia
Ataxia is a neurological sign and symptom that consists of gross lack of coordination of muscle movements. Ataxia is a non-specific clinical manifestation implying dysfunction of the parts of the nervous system that coordinate movement, such as the cerebellum...
without muscle weakness.
Patients may report minor sensory symptoms, but constitutional signs are usually absent. Deep tendon reflexes are usually hypoactive or absent, and ophthalmoplegia and bulbar palsy
Bulbar palsy
Bulbar palsy refers to impairment of function of the cranial nerves IX, X, XI and XII, which occurs due to a lower motor neuron lesion either at nuclear or fascicular level in the medulla oblongata or from lesions of the lower cranial nerves outside the brainstem.In contrast, pseudobulbar palsy...
can occur.
Electromyographic
Electromyography
Electromyography is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG is performed using an instrument called an electromyograph, to produce a record called an electromyogram. An electromyograph detects the electrical potential generated by muscle...
(EMG) studies usually show a variable reduction in the amplitude of compound muscle action potential
Action potential
In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...
s, but no abnormalities of repetitive nerve stimulation studies. These appear to result from a failure of acetylcholine release at the motor nerve terminal level. There may be subtle abnormalities of motor nerve
Nerve
A peripheral nerve, or simply nerve, is an enclosed, cable-like bundle of peripheral axons . A nerve provides a common pathway for the electrochemical nerve impulses that are transmitted along each of the axons. Nerves are found only in the peripheral nervous system...
conduction velocity and sensory action potentials.
Pathogenesis
Tick paralysis is believed to be due to toxins found in the tick's saliva that enter the bloodstream while the tick is feeding. The two ticks most commonly associated with North American tick paralysis are the Rocky Mountain wood tick (Dermacentor andersoniDermacentor andersoni
Dermacentor andersoni, commonly known as the Rocky Mountain wood tick, is a species of tick.It can cause tick paralysis.Diagnostic features:Larva only has 3 pairs of legs.Nymph has 4 pairs....
) and the American dog tick (Dermacentor variabilis
Dermacentor variabilis
Dermacentor variabilis, also known as the American dog tick, is a species of tick that is known to carry bacteria responsible for several diseases in humans, including Rocky Mountain spotted fever and tularemia . It is one of the most well-known hard ticks.Though D...
); however, 43 tick species have been implicated in human disease around the world. Most North American cases of tick paralysis occur from April to June, when adult Dermacentor ticks emerge from hibernation and actively seek hosts. In Australia, tick paralysis is caused by the tick Ixodes holocyclus. Prior to 1989, 20 fatal cases were reported in Australia.
Tick paralysis has killed thousands of animals, mainly cows and sheep, in other parts of the world. Although tick paralysis is of concern in domestic animals and livestock in the United States as well, human cases are rare and usually occur in children under the age of 10.
Tick paralysis occurs when an engorged and gravid (egg-laden) female tick produces a neurotoxin
Neurotoxin
A neurotoxin is a toxin that acts specifically on nerve cells , usually by interacting with membrane proteins such as ion channels. Some sources are more general, and define the effect of neurotoxins as occurring at nerve tissue...
in its salivary glands and transmits it to its host during feeding. Experiments have indicated that the greatest amount of toxin is produced between the fifth and seventh day of attachment (often initiating or increasing the severity of symptoms), although the timing may vary depending on the species of tick.
Unlike Lyme disease
Lyme disease
Lyme disease, or Lyme borreliosis, is an emerging infectious disease caused by at least three species of bacteria belonging to the genus Borrelia. Borrelia burgdorferi sensu stricto is the main cause of Lyme disease in the United States, whereas Borrelia afzelii and Borrelia garinii cause most...
, ehrlichiosis
Ehrlichiosis
Ehrlichiosis is a tick-borne disease of dogs usually caused by the organism Ehrlichia canis. Ehrlichia canis is the pathogen of animals. Humans can become infected by E. canis and other species after tick exposure. German Shepherd dogs are thought to be particularly affected by the disease, other...
, and babesiosis
Babesiosis
Babesiosis is a malaria-like parasitic disease caused by infection with Babesia, a genus of protozoal piroplasms. After trypanosomes, Babesia are thought to be the second most common blood parasites of mammals and they can have a major impact on health of domestic animals in areas without severe...
, which are caused by the systemic proliferation and expansion of parasites in their hosts long after the offending tick is gone, tick paralysis is chemically induced by the tick and therefore usually only continues in its presence. Once the tick is removed, symptoms usually diminish rapidly. However, in some cases, profound paralysis can develop and even become fatal before anyone becomes aware of a tick's presence.
Diagnostic tests
Diagnosis is based on symptoms and upon finding an embedded tick, usually on the scalp.In the absence of a tick, the differential diagnosis includes Guillain-Barre syndrome
Guillain-Barré syndrome
Guillain–Barré syndrome , sometimes called Landry's paralysis, is an acute inflammatory demyelinating polyneuropathy , a disorder affecting the peripheral nervous system. Ascending paralysis, weakness beginning in the feet and hands and migrating towards the trunk, is the most typical symptom...
.
Treatment
Removal of the embedded tick usually results in resolution of symptoms within several hours to days. If the tick is not removed, the toxin can be fatal, with reported mortality rates of 10–12 percent, usually due to respiratory paralysis. The tick is best removed by grasping the tick as close to the skin as possible and pulling in a firm steady manner.Prevention
No vaccineVaccine
A vaccine is a biological preparation that improves immunity to a particular disease. A vaccine typically contains an agent that resembles a disease-causing microorganism, and is often made from weakened or killed forms of the microbe or its toxins...
is currently available for any tick-borne disease, except for Tick-borne encephalitis. Individuals should therefore take precautions when entering tick-infested areas, particularly in the spring and summer months. Preventive measures include avoiding trails that are overgrown with bushy vegetation, wearing light-coloured clothes that allow one to see the ticks more easily, and wearing long pants and closed-toe shoes. Tick repellents containing DEET
DEET
N,N-Diethyl-meta-toluamide, abbreviated DEET, is a slightly yellow oil. It is the most common active ingredient in insect repellents...
(N,N, diethyl-m-toluamide) are only marginally effective and can be applied to skin or clothing. Rarely, severe reactions can occur in some people who use DEET-containing products. Young children may be especially vulnerable to these adverse effects. Permethrin
Permethrin
Permethrin is a common synthetic chemical, widely used as an insecticide, acaricide, and insect repellent. It belongs to the family of synthetic chemicals called pyrethroids and functions as a neurotoxin, affecting neuron membranes by prolonging sodium channel activation. It is not known to...
, which can only be applied to clothing, is much more effective in preventing tick bites. Permethrin is not a repellent but rather an insecticide; it causes ticks to curl up and fall off the protected clothing.
Toxin
Although several attempts have been made to isolate and identify the neurotoxinNeurotoxin
A neurotoxin is a toxin that acts specifically on nerve cells , usually by interacting with membrane proteins such as ion channels. Some sources are more general, and define the effect of neurotoxins as occurring at nerve tissue...
since the first isolation in 1966, the exact structure of the toxin is still unknown. The 40-80 kDa protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
fraction contains the toxin.