Tick paralysis

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Tick paralysis
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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. Patients can experience severe respiratory distress (similar to anaphylaxis).


Signs and symptoms

Tick paralysis results from injection of a toxin from tick salivary glands during a blood meal. The toxin causes symptoms 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, such as local numbness, but constitutional signs are usually absent. Deep tendon reflexes are usually decreased or absent, and ophthalmoplegia and bulbar palsy can occur.

Electromyographic (EMG) studies usually show a variable reduction in the amplitude of compound muscle action potentials, 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.


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 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 from April to June, when adult Dermacentor ticks emerge from hibernation and actively seek hosts. [2] In Australia, tick paralysis is caused by the tick Ixodes holocyclus . Prior to 1989, 20 fatal cases were reported in Australia. [3]

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.


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–Barré syndrome. Early signs of tick poisoning could be a change of an animals' ‘voice’, weakness in the back legs or vomiting.[ citation needed ]


No human vaccine 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.[ weasel words ]


Removal of the offending tick usually results in resolution of symptoms within several hours to days. If the tick is not removed, the toxin can be fatal. A 1969 study of children reported mortality rates of 10 – 12 percent, [4] mostly due to respiratory paralysis. The tick is best removed by grasping it as close to the skin as possible and pulling in a firm steady manner. [5] Because the toxin lies in the tick's salivary glands, care must be taken to remove the entire tick (including the head), or symptoms may persist.

It is important to note that, unlike the toxin of other tick species, the toxin of Ixodes holocyclus (Australian Paralysis Tick) may still be fatal even if the tick is removed.

For affected animals, food and water intake can worsen the outcome, as the toxin can prevent the animal from swallowing properly. If you find a tick on your animal, remove it immediately and seek veterinary assistance if the animal shows any signs of illness. The tick can be placed in a tightly sealed plastic bag and taken to a veterinarian for identification. [6] [7]


Although several attempts have been made to isolate and identify the neurotoxin since the first isolation in 1966, the exact structure of the toxin has still not been published. [8] The 40-80 kDa protein fraction contains the toxin. [9]

The neurotoxin structure and gene, at least for the tick species Ixodes holocyclus have since been identified and are called holocyclotoxins after the species. At least three members (HT-1 [10] , HT-3 [11] , and HT-12 [12] ) trigger paralysis by presynaptic inhibition of neurotransmitter release via a calcium dependent mechanism resulting in a reduction of quantal content, and loss of effective neuromuscular synaptic transmission. [13]


In the TV show, Hart of Dixie , Season 1, Episode 2, a patient is diagnosed with tick paralysis who has been deer hunting.

In the TV show, Emergency! , Season 5, Episode 4, "Equipment" (first aired Oct. 4, 1975), Dr. Joe Early diagnoses a young boy who has fallen from a tree with tick paralysis, after eliminating polio as a cause. [14]

In the TV show, House , Season 2, Episode 16, "Safe", Dr House diagnoses a patient (played by Michelle Trachtenberg) with tick paralysis. [15]

In the TV show, Remedy , Season 1 Episode 7, "Tomorrow, the Green Grass", Rebecca is diagnosed with tick paralysis.

In the TV show, Royal Pains , Season 1 Episode 3, "Strategic Planning", a US Senator's teenage son is diagnosed with and overcomes tick paralysis.

In the TV show, Chicago Med , Season 3, Episode 5, "Mountains and Molehills", a young girl returning from Australia with increasing paralysis is diagnosed with tick paralysis.

See also

Related Research Articles

Paralysis is a loss of motor function in 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. In the United States, roughly 1 in 50 people have been diagnosed with some form of permanent or transient paralysis. The word comes from the Greek παράλυσις, "disabling of the nerves", itself from παρά (para), "beside, by" and λύσις (lysis), "making loose". A paralysis accompanied by involuntary tremors is usually called "palsy".

<i>Clostridium botulinum</i> species of bacterium

Clostridium botulinum is a Gram-positive, rod-shaped, anaerobic, spore-forming, motile bacterium with the ability to produce the neurotoxin botulinum.

Tick Order of arachnids in the arthropod phylum

Ticks (Ixodida) are arachnids, typically 3 to 5 mm long, part of the superorder Parasitiformes. Along with mites, they constitute the subclass Acari. Ticks are external parasites, living by feeding on the blood of mammals, birds, and sometimes reptiles and amphibians. Ticks evolved by the Cretaceous period, the most common form of fossilisation being amber immersion. Ticks are widely distributed around the world, especially in warm, humid climates.

Ixodidae family of arachnids

The Ixodidae are the family of hard ticks or scale ticks, one of the two big families of ticks, consisting of over 700 species. They are known as 'hard ticks' because they have a scutum or hard shield, which the other big family of ticks, the 'soft ticks' (Argasidae), lack. They are ectoparasites of a wide range of host species, and some are vectors of pathogens that can cause human disease.

Lyme disease Infectious disease caused by Borrelia bacteria, spread by ticks

Lyme disease, also known as Lyme borreliosis, is an infectious disease caused by the Borrelia bacterium which is spread by ticks. The most common sign of infection is an expanding area of redness on the skin, known as erythema migrans, that appears at the site of the tick bite about a week after it occurred. The rash is typically neither itchy nor painful. Approximately 70–80% of infected people develop a rash. Other early symptoms may include fever, headache and tiredness. If untreated, symptoms may include loss of the ability to move one or both sides of the face, joint pains, severe headaches with neck stiffness, or heart palpitations, among others. Months to years later, repeated episodes of joint pain and swelling may occur. Occasionally, people develop shooting pains or tingling in their arms and legs. Despite appropriate treatment, about 10 to 20% of people develop joint pains, memory problems, and tiredness for at least six months.

Tick-borne diseases, which afflict humans and other animals, are caused by infectious agents transmitted by tick bites. They are caused by infection with a variety of pathogens, including rickettsia and other types of bacteria, viruses, and protozoa. Because individual ticks can harbor more than one disease-causing agent, patients can be infected with more than one pathogen at the same time, compounding the difficulty in diagnosis and treatment. 16 tick-borne diseases of humans are known, of which four have been discovered since 2013.

Parotitis parotid disease characterized by the inflammation of one or both parotid glands

Parotitis is an inflammation of one or both parotid glands, the major salivary glands located on either side of the face, in humans. The parotid gland is the salivary gland most commonly affected by inflammation.

<i>Ixodes holocyclus</i> species of arachnid

Ixodes holocyclus, commonly known as the Australian paralysis tick, is one of about 75 species of Australian tick fauna and is considered the most medically important. It can cause paralysis by injecting neurotoxins into its host. It is usually found in a 20-kilometre wide band following the eastern coastline of Australia. Within this range Ixodes holocyclus is the tick most frequently encountered by humans and their pets. As this area also contains the majority of Australia's most densely populated regions, incidents of bites on people, pets and livestock are relatively common.

Polyneuropathy in dogs and cats is a collection of peripheral nerve disorders that often are breed-related in these animals. Polyneuropathy indicates that multiple nerves are involved, unlike mononeuropathy. Polyneuropathy usually involves motor nerve dysfunction, also known as lower motor neuron disease. Symptoms include decreased or absent reflexes and muscle tone, weakness, or paralysis. It often occurs in the rear legs and is bilateral. Most are chronic problems with a slow onset of symptoms, but some occur suddenly.

<i>Dermacentor variabilis</i> species of arachnid

Dermacentor variabilis, also known as the American dog tick or wood 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 best-known hard ticks. Diseases are spread when it sucks blood from the host. It may take several days for the host to experience symptoms.

<i>Babesia</i> genus of protozoan parasites

Babesia, also called Nuttallia, is an Apicomplexan parasite that infects red blood cells, transmitted by ticks. Originally discovered by the Romanian bacteriologist Victor Babeș, over 100 species of Babesia have since been identified.

Powassan virus (POWV) is a Flavivirus transmitted by ticks, found in North America and in the Russian Far East. It is named after the town of Powassan, Ontario, where it was identified in a young boy who eventually died from it. It can cause encephalitis, an infection of the brain. No vaccine or antiviral drug exists. Prevention of tick bites is the best precaution.

Anaplasmosis disease, mostly animal (cattle) also in humans, caused by bacteria of the genus Anaplasma

Anaplasmosis is a disease caused by a rickettsial parasite of ruminants, Anaplasma spp and is therefore related to rickettsial disease. The microorganisms are Gram-negative, and infect red blood cells. They are transmitted by natural means through a number of haematophagous species of ticks. The Ixodes tick that commonly transmits Lyme disease also spreads anaplasmosis.

<i>Ixodes scapularis</i> parasit ixodes scapularis

Ixodes scapularis is commonly known as the deer tick or black-legged tick, and in some parts of the US as the bear tick. It is a hard-bodied tick found in the eastern and northern Midwest of the United States as well as in southeastern Canada. It is a vector for several diseases of animals, including humans and is known as the deer tick owing to its habit of parasitizing the white-tailed deer. It is also known to parasitize mice, lizards, migratory birds, etc. especially while the tick is in the larval or nymphal stage.

<i>Ixodes ricinus</i> species of hard-bodied tick

Ixodes ricinus, the castor bean tick, is a chiefly European species of hard-bodied tick. It may reach a length of 11 mm (0.43 in) when engorged with a blood meal, and can transmit both bacterial and viral pathogens such as the causative agents of Lyme disease and tick-borne encephalitis.

Powassan encephalitis, caused by the Powassan virus (POWV), a flavivirus also known as the deer tick virus, is a form of arbovirus infection that results from tick bites. It can occur as a co-infection with Lyme disease since both are transmitted to humans by the same species of tick. There has been a surge in the number of cases and geographic range in the last decade. In the United States, cases have been recorded in the northeast. The disease was first isolated from the brain of a boy who died of encephalitis in Powassan, Ontario, in 1958. The disease is a zoonosis, an animal disease, usually found in rodents and ticks, with spillover transmission to humans. The virus is antigenically related to the Far Eastern tick-borne encephalitis viruses.

Human granulocytic anaplasmosis human disease

Human granulocytic anaplasmosis (HGA) is a tick-borne, infectious disease caused by Anaplasma phagocytophilum, an obligate intracellular bacterium that is typically transmitted to humans by ticks of the Ixodes ricinus species complex, including Ixodes scapularis and Ixodes pacificus in North America. These ticks also transmit Lyme disease and other tick-borne diseases.

Rickettsia helvetica, previously known as the Swiss agent, is a bacterium found in Dermacentor reticulatus and other ticks, which has been implicated as a suspected but unconfirmed human pathogen. First recognized in 1979 in Ixodes ricinus ticks in Switzerland as a new member of the spotted fever group of Rickettsia, the R. helvetica bacterium was eventually isolated in 1993. Although R. helvetica was initially thought to be harmless in humans and many animal species, some individual case reports suggest that it may be capable of causing a nonspecific fever in humans. In 1997, a man living in eastern France seroconverted to Rickettsia 4 weeks after onset of an unexplained febrile illness. In 2010, a case report indicated that tick-borne R. helvetica can also cause meningitis in humans.

Ticks of domestic animals variety of ticks affecting domestic animals

Ticks of domestic animals directly cause poor health and loss of production to their hosts by many parasitic mechanisms. Ticks also transmit numerous kinds of viruses, bacteria, and protozoa between domestic animals. These microbes cause diseases which can be severely debilitating or fatal to domestic animals, and may also affect humans. Ticks are especially important to domestic animals in tropical and subtropical countries, where the warm climate enables many species to flourish. Also, the large populations of wild animals in warm countries provide a reservoir of ticks and infective microbes that spread to domestic animals. Farmers of livestock animals use many methods to control ticks, and related treatments are used to reduce infestation of companion animals.

Ixodes cornuatus, commonly known as the Tasmanian paralysis tick, is one of about 75 species of Australian tick fauna. It is found across Tasmania and Victoria. It has been responsible for several cases of evenomation in humans and the death of one cat.


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