Paralysis and a head lump

aka Toxicology Conundrum 039

A 5 year old girl is brought to the emergency department as she is unable to walk. The day before she had started to become unsteady on her feet. Since then she has got progressively weaker.

The child has flaccid paralysis of all limbs and absent knee jerks. She is having difficulty clearing secretions and is obtunded; she rouses to voice. Examination of the eyes reveals that her pupils are equal and reactive to light, but she has nystagmus.

As you examine the child, her mother remembers that the girl complained of a lump on her head a few days ago. You examine her scalp and remove an almond-sized organism that looks like this:

ixodes holocyclus

On further inquiry, the child’s mother mentions that they attended a picnic in bush land near Sydney a week previously.


Q1. What is the likely diagnosis?

Answer and interpretation

Tick paralysis

A high index of suspicion is required to make the diagnosis in cases of ataxia or paralysis where patients are from, or have visited, regions where the causative species are endemic.

Q2. What are the causative organisms and where are they found?

Answer and interpretation

The photo shows an engorged hard tick Ixodes holocyclus.

Although there are over 70 species of tick in Australia only 3 species of ixodid or ‘hard’ tick cause tick paralysis:

  • Ixodes holocyclus
  • Ixodes hirsti
  • Ixodes cornuatus

These ticks are confined to the bush and scrub lands near the eastern coast of Australia, from North Queensland to Victoria. Tick paralysis has also been reported in Tasmania. There are less than 5 cases of severe envenoming each year in Australia. There have been no deaths since 1945 and the advent of improved respiratory support, but tick paralysis has accounted for more deaths than either the red back spider or the funnel web spider in Australia.

Both male and female adult ticks attach onto humans. They do this by ‘questing‘ — they climb up vegetation waiting for host to pass by. Natural hosts in Australia include bandicoots, koalas, possums and kangaroos.

Distribution of Ixodes species in Australia. From Roberts, FHS (1970)

Tick paralysis also occurs in many other parts of the world where members of the Ixodidae family are found:

  • Dermacentor andersoni — Western United States and Canada (British Columbia)
  • D. variabilis — Central and Eastern United States
  • Ixodes holocyclus and I. hirsti — Eastern Australia
  • I. cornuatus — Tasmania (Australia)
  • I. tancitarius — Mexico
  • I. rubicundus — Africa
  • Rhipicephalus simus — South Africa, Somalia
  • R. evertsi evertsi — Africa

Q3. What are the usual clinical manifestations of this condition?

Answer and interpretation

Clinical manifestations:

  • onset of symptoms is usually 4-5 days after tick attachment
  • there may be local itch and swelling at the tick attachment site. Local nerve palsies (e.g. CN7 palsy) may occur in proximity to the tick attachment site. Allergic reactions may occur.
  • systemic toxicity is heralded by a nonspecific prodrome of ataxia (unsteady gait) and drowsiness or lethargy.
  • a progressive ascending symmetrical flaccid paralysis occurs over a period of days.
  • eventually cranial nerve palsies occur — typically ptosis, extraocular palsies, CN7 palsies, dysphagia and impaired airway reflexes.
  • death may result following the onset of respiratory paralysis.

Severe toxicity and death is usually seen in children under the age of 3 years.

Q4. What mediates the systemic toxicity?

Answer and interpretation

Ixodid ticks contain neurotoxins in their saliva, in addition to various agents that modulate the hemostatic and inflammatory responses of the host. In the case of I. holocyclus, the neurotoxins are ~ 5 kDa proteins known as holocyclotoxins. These toxins appear to impair acetylcholine release from presynaptic nerve terminals.

Ixodes holocyclus tick, before and after feeding: Bjørn Christian Tørrissen

Q5. How is the causative organism removed?

Answer and interpretation

Use fine forceps or suture material to grasp the tick’s mouth parts close to the skin at the site of attachment. Remove the tick, with mouth-parts intact, by carefully applying steady traction.

Don’t worry about twisting clockwise or anti-clockwise!

There is controversy about whether the tick should be killed before removal, due to concerns about toxin release during removal. More important is to ensure that there are no retained mouth-parts, which may lead to granuloma formation.

Q6. Can clinical deterioration occur following removal of the causative organism?

Answer and interpretation


In the Australian setting, paralysis may progress for about 2 days following the removal of the tick in the symptomatic patient. The asymptomatic patients does not need to be admitted for observation following the removal of a tick!

Q7. How is this condition managed?

Answer and interpretation


  • Resuscitation
    • Life threats include loss of airway reflexes and respiratory paralysis
    • Intubation and ventilation may be required, and once performed is usually continued for day to weeks.
  • Supportive care and monitoring
    • Spirometry or serial peak expiratory flow monitory may be used to monitor the progression of respiratory paralysis
    • Regular neurological observations
    • Removal of the tick as soon as possible
  • Disposition
    • Patients with the potential for respiratory failure require HDU/ ICU level care
    • Symptomatic patients should not be discharged until ongoing neurological recovery is observed

Q8. What is the role of antivenom?

Answer and interpretation

CSL Tick paralysis antivenom is no longer available for use in humans.

Patient survival can be ensured by meticulous supportive care and ventilatory support.

  • Brown AF, Hamilton DL. Tick bite anaphylaxis in Australia. J Accid Emerg Med. 1998 Mar;15(2):111-3. PMC1343038.
  • Edlow JA, McGillicuddy DC. Tick paralysis. Infect Dis Clin North Am. 2008 Sep;22(3):397-413, vii. PMID: 18755381.
  • Grattan-Smith PJ, Morris JG, Johnston HM, Yiannikas C, Malik R, Russell R, Ouvrier RA. Clinical and neurophysiological features of tick paralysis. Brain. 1997 Nov;120 ( Pt 11):1975-87. PMID: 9397015.


Toxicology Conundrum

Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of three amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

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