Ticks

Ticks are arachnids that obtain blood for nourishment. There are over 70 species in Australia but only three that cause paralysis: Ixodes holocyclus (almost always the culprit). Ixodes cornuatus and Ixodes hirsti.

It will be unsurprising that ticks have haemostat and anti-inflammatory agents in their saliva to facility feeding but the above 3 species also contain a neurotoxin known as holocyclotoxin that binds to the pre-synaptic neuromuscular junction and inhibits the release of acetylcholine. The feared complication is tick paralysis but this is rare and more likely to occur in infants.

Resus

Potential life threats include:

• Respiratory failure, intubation and ventilation maybe required (days to weeks)

Risk Assessment

• Geography: On the east coast between Cairns in the North and Bairnsdale in the South.

Typical symptoms include:

• Non-specific prodrome of drowsiness, unsteady gait followed by a progressive ascending paralysis over the coming days. Cranial nerve involvement results in ocular paralysis, ptosis and facial paralysis.
• Paralysis can progress for a further 48 hours from tick removal
• Death can result from repository failure
• Recovery may take weeks
• Remember this section does not include the potential for the infectious disease caused by ticks (babesiosis, Rocky Mountain spotted fever, anaplasmosis, tularaemia, Colorado tick fever, tick-borne replacing fever and Lyme disease – some of which are present rarely in Australia).

Supportive Care

• Tick removal Search everywhere (in the hair – favourite place, behind ears, in the auditory canal, nose, perineum, natal cleft). Grasp the tick close to the skin using fine forceps, aiming to take all the mouth parts out with the tick. Gently pull to the tick off.

Investigations

• Tick paralysis is a clinical diagnosis but investigations should be directed at excluding alternative causes (Guillian Barre syndrome, infant botulism or paralysis from snake bite or tetrodotoxin).
• If done nerve conduction studies in tick paralysis will show a reduced amplitude of compound motor action potential but normal conduction velocities. Sensory nerve will be normal.

Differential Diagnosis:

• Guillian Barre Syndrome
• Poliomyelitis
• Transverse myelitis
• Myasthenia gravis
• Periodic Paralysis
• Acute cerebellar ataxia and spinal cord lesions
• Infant Botulism
• Snake bite envenomation – tiger, taipan and black (will cause a VICC), death adder and sea snake
• Blue ringed octopus
• Ingestion of puffer fish

Antivenom

• None available

Disposition

• Patients are admitted if symptomatic for close observation. If discharging patients who are asymptomatic they will need to be informed of the potential for complications and be in an area capable of providing ICU level of care if required (no going for a week in the bush).
• Patients requiring ventilatory support will need ICU and a subsequent admission for rehabilitation

References:

• Edlow JA, McGillicuddy DC. Tick paralysis. Infectious Disease Clinics of North America 2008; 22:397-413
• Grattan-Smith PJ, Morris JG, Johnston HM et al. Clinical and neurophysiological features of tick paralysis. Brain 1997; 120:1975-1987
• White J. A clinician’s guide to Australian venomous bites and stings: Incorporating the updates CSL antivenom handbook. Melbourne: CSL Ltd. 2012