Ticks

Question 1

Paralysis tick

Ixodes holocyclus

Answer 1

• Native to eastern coast of Australia
• Canine mortality rate of 4-10%
• Most active from August to February, but like warm, humid conditions (can be present year-round)
• Adult females cause majority of envenomations, female nymphs can when present in high numbers

Question 2

Tick feeding

Answer 2

• Attaches firmly using external mouthparts, feed on the blood
• During feeding they release Holocyclotoxins contained in their saliva
• They enter the lymphatic system of the host and travel via systemic circulation

Question 3

Tick toxins

Answer 3

• Toxin acts on neuromuscular junctions, cellular potassium channels, consequently intracellular calcium channels, inhibiting acetylcholine release causing a gradual ascending paralysis
• Disruption to potassium channels and intracellular calcium levels may cause a reduction in myocardial contractility leading occasionally to pulmonary oedema and electrical failure of the heart
• The respiratory system is commonly compromised in mild to severe cases of tick paralysis. May result in death
• Complications of upper respiratory laryngeal paralysis and megaoesophagus can lead to aspiration pneumonia

Question 4

Complications as a result of the toxin/disease

Answer 4

• Aspiration pneumonia
• Respiratory distress to failure
• Laryngeal dysfunction
• Megaoesophagus
• Cardiotoxic effects (myocardial depression/failure)
• Stress/anxiety
• Regurgitation/obstruction

Question 5

Complications as a result of paralysis

Answer 5

• Corneal ulcers
• Pressure sores
• Inability to thermoregulate
• Muscle wastage
• Bladder atony/overflow incontinence

Question 6

Onset of symptoms

Answer 6

• Typically 3-5 days post attachment
• May develop clinical signs or deteriorate for 12-24 hours after removal due to delayed action of toxins on the neuromuscular junction

Question 7

Clinical signs

Answer 7

• Change in vocalisation
• Hind limb weakness/ataxia
• Coughing/gagging
• Vomiting/retching/regurgitating
• Change in respiration (increased effort, altered rate or depth)
• Gradual ascending paralysis of limbs, head, and respiratory system.
• Inability to right themselves appropriately (even into sternal recumbency)

Question 8

Grading score overview

Answer 8

• Score depends on the degree of paralysis (1-4) and on respiratory effort (A-D)
• May be updated throughout hospitalisation

Question 9

Neuromuscular Score (1-4)

Answer 9

1 – Ataxia (impaired coordination)
2 – Can stand but not walk
3 – Cannot stand but able to maintain sternal recumbency
4 – Lateral recumbency, cannot right itself

Question 10

Respiratory Score (A-D)

Answer 10

A – Normal respiratory effort
B – Mild respiratory effort
C – Moderate respiratory effort
D – Severe respiratory effort, cyanosis

Question 11

Differential diagnosis for ticks

Answer 11

• Snake bite
• Botulism
• Tetrodotoxins (Pufferfish toxin)
• Ciguatera toxin (Reef fish toxin)
• Myasthenia gravis
• Polyridiculoneuritis
• Organophosphate intoxication
• Thromboembolic disease
• Meningitis/Myelitis
• Spinal disease

Question 12

Diagnosis

Answer 12

• Combination of clinical signs observed with the presence of an engorged tick or tick crater on the patient
• If cannot find a tick a diagnostic tick clip may be considered

Question 13

Appearance of ticks

Answer 13

• May vary in their appearance depending on their life stage and whether they are fed or unfed
• Legs: All grouped around the mouth parts
• Legs: 1st and 4th set of legs are darker brown, the 2nd and 3rd sets of legs are pale in comparison
• Anal groove: Has a complete oval around the anus
• Mouth parts: Long

Question 14

Treatment

Answer 14

• Depends on severity/grading score
• Unaffected patient may be sent home for monitoring for next 24-48 hours
• At least 10% of patients with a tick present have another tick elsewhere
• Tick clips/searching
• Tick antiserum (TAS), hospitalisation, fluid therapy, sedation and nursing care

Question 15

Administration of Tick Antiserum

Answer 15

• Blood product collected from hyperimmune dogs
• TAS quickly neutralises Holocyclotoxins present in the blood stream
• Unable to reverse the effects of bound toxins
• Purified TAS is a specialised product that’s filtered/concentrated to remove albumen and alpha globulin protein factors
• This product is available in limited quantities (not commercially available 2020) but is safer for use in cats, especially those who have previously received TAS and are at high risk of developing anaphylaxis on repeat exposure
• Closely monitor for transfusion complications including systemic anaphylaxis, Bezhold Jarisch (BJ) reactions, or hives/facial angioedema reactions.