Across the globe, there are more than 40 species that cause tick paralysis. While only five of those species live in North America, the common deer tick is one of them and is found in any area where there are ticks. In the US, thousands of livestock and domestic animals have been killed by tick paralysis. However, it is much rarer in humans and is most frequently seen in children under 10 years of age.
Tick paralysis was first described in 1824 in the outback of Australia. William Howell referred to a tick in his diary “which buries itself in the flesh and would in the end destroy either man or beast if not removed on time”. In 1912, it was observed in Canada. Although it is now known to happen globally, it is most common in Australia and North America. Because it is not a reportable disease and is not being tracked, accurate data does not exist. In spite of the fact that there have been cases in the southern, eastern, and southeastern US, the majority of the cases are observed in the western regions. Tick paralysis is more common in females.
In North America, tick paralysis is usually transmitted by the Dermacentur variabilis and the Dermacentur andersoni ticks depending on the region. It usually occurs in the spring and summer months and most commonly affects girls with long hair, mostly likely because ticks are hidden by the hair. It has recently been suggested that many cases of tick paralysis have been misdiagnosed as Guilliane-Barre syndrome (GBS), perhaps skewing the true incidence of the disease. In one study, researchers conducted a review and analysis of the scientific literature looking at the incidence of tick paralysis in the US. They discovered that more case of tick paralysis are being misdiagnosed as GBS and healthcare workers failed to search for ticks in these cases.
Tick paralysis is unique in the fact that it is the only disease where a tick vector does not transmit a disease through an infectious organism. Rather, a neurotoxin produced in the tick’s salivary gland is thought to cause the paralysis. Typically, ascending paralysis emerges after 2-7 days following a bite from a pregnant tick. Respiratory failure and death may ensure. Rarely, a patient may present with ataxia without the paralysis.
What are the symptoms of tick paralysis?
- Ataxia (lack of muscle coordination with voluntary movements like walking) followed by ascending paralysis starting in the feet and legs
- Fever (rare)
- Malaise and listlessness
- Reduced or absent reflexes in the affected area
- Sensory abnormalities
- Respiratory symptoms, which can be fatal
- Involvement of the cranial nerves (rare and not seen in the absence of other neurologic deficits)
In the case of tick paralysis, the paralysis tends to develop very slowly. One group of researcher described a prodrome followed by an unsteady gait and then an ascending, symmetrical paralysis evolving over days. Death usually results from respiratory arrest if the tick is not removed. In children who recover, the weakness may take several weeks to resolve. Cranial nerve involvement is rare but when it does occur, bulbar and facial paralysis are most often seen. Additionally, pupillary reaction and extra-ocular muscle movement impairment have also been noted. The ocular signs were noted early in the disease and may provide a clue that GBS is not the cause. Even rarer complications include myocarditis and myositis. If a patient continues to deteriorate after the removal of a tick, it is a strong indication that the paralysis is caused by the Ixodes holocyclus tick.
The exact pathophysiology of tick paralysis remains unclear. Nerve conduction velocities and nerve action potentials are found to be normal. It appears that the neurotoxin inhibits the synthesis or release of acetylcholine (AcH) at peripheral nerve terminals. Animal studies demonstrate a significant reduction in muscle compound action potentials evoked by nerve stimulation. The spontaneous release of AcH at rest was normal. However, there was a temperature-dependent inhibition noted. Even when the nerves were unresponsive, the muscles contracted normally with direct muscle stimulation. This suggests that the site of action of the toxin is at the neuromuscular junction. It is possible that the toxins of different ticks act in different ways.
The diagnosis of tick paralysis is made based on suggestive symptoms and the discovery of a tick on a patient’s body. Usually symptoms occur once the tick becomes engorged. Treatment consists of completely removing the tick as soon as discovered. It is best to use forceps or tweezers and grasp the tick as closely to the skin as possible. It should be removed using steady traction to avoid breaking off parts of the tick and leaving any inside the patient.
Tick paralysis is often misdiagnosed as GBS, especially the Miller’s Fisher subtype. In tick paralysis, studies of the blood and CSF are normal. In contrast, there is typically an elevation of protein in the CSF of patients with GB. Additionally, the weakness and paralysis progresses more quickly in tick paralysis than GB. One meta-analysis study shows that more patients are misdiagnosed and treated for GB today than in previous years.
In cases where the tick paralysis is misdiagnosed and mistreated, the mortality rate is approximately 10%. Death commonly occurs 18-30 hours after symptom onset. Symptoms typically begin 4-7 days after the tick attaches to the patient. It starts secreting the neurotoxin on Day #3, making timely removal of any attached ticks critical. The treatment, as mentioned above, is simply removing the tick.
The cornerstone of tick-borne diseases and its treatment remains prevention. It is important to know what ticks are in a given area and patients should be education regarding these diseases, especially their signs and symptoms. Avoiding the tick bite should be the first goal and this can be achieved using insect repellant containing Deet and wearing long-sleeves and pants when outdoors. Tick checks should be done, especially on children, when coming in from outdoors. And when a clinician encounters an ascending paralysis in a patient, especially a pediatric one, check for ticks. It is non-invasive and doesn’t cost anything extra. If you do find a tick, you can save a patient’s life with a simple removal. If you live in an endemic area, tick-borne diseases should be included on the differential diagnosis.
About the Author
Linda Girgis MD, FAAFP is a family physician practicing in South River, New Jersey and Clinical Assistant Professor at Rutgers Robert Wood Johnson Medical School. She was voted one of the top 5 healthcare bloggers in 2016. Follow her on twitter @DrLindaMD.