Tick Paralysis – Clinical Signs and Diagnosis

Enhance your veterinary skills and treat your next Tick Paralysis case with our handy guide to tick paralysis clinical signs and diagnosis.

As Spring comes around once again and the beautiful weather begins to return, there’s one fatal disease that looms over the conscience of many Australian vets during this season: Tick Paralysis.

If you’ve worked in clinical practice in Australia, particularly those vets among you situated along the country’s eastern border, there’s a high likelihood you’ve encountered Ixodes holocyclus, the infamous Paralysis Tick. The tiny parasite that’s the bane of many vets’ existence!

We’ve all faced challenging tick cases in the past – from missed diagnoses, tricky critical patients requiring intensive care or ventilation, and those especially sticky situations where even the treatment itself can at times add to the problem list.

That’s why we’ve put together this handy step-by-step guide to managing tick paralysis. From diagnosis and clinical signs through to treatment and aftercare, we’ll tick off each step over the next 5 articles over the coming weeks to ensure you’re prepared and ready to conquer your next tick case with confidence.

Tick Paralysis Clinical Signs

Picture a typical patient affected by tick paralysis – this might include hindlimb paresis and ataxia, perhaps retching or vomiting, or even full-blown tetraparesis with respiratory distress. Though as many of us well know, most patients are rarely kind enough to follow the textbook.

Clinical signs can for tick paralysis vary from completely absent or sneakily subtle, through to the glaringly obvious. For a start, any patients exhibiting the following clinical signs of tick toxicity require immediate treatment:

Ascending paralysis
Respiratory distress/tachypnea
Changes in phonation
Regurgitation

The early signs are often subtle and may occur singly and may go unnoticed by both owner and veterinary professional without a professional assessment. It’s vital that any of the following clinical signs could be reasonable suspicion to consider a tick on your list of differentials:

Vomiting
Mild ataxia
Unilateral lameness
General weakness
Inappetence
Tachypnea

Clinical signs can then be graded on severity, which will aid triage. Grading is achieved by assigning a numerical score to the paralysis, and a letter score to the degree of respiratory compromise. Animals with severe respiratory distress or cyanosis (Respiratory Score D) should be taken to the treatment room and immediately be given fly-by oxygen and administered appropriate sedation if necessary.

Tick Paralysis Scoring

Gait Score

1. Mild ataxia or paresis

2. Able to stand/sit unaided, but cannot walk

3. Unable to stand, can maintain sternal recumbency

4. Unable to maintain sternal recumbency

Respiratory Score

A. No clinical respiratory compromise

B. Mild respiratory compromise – tachypnoeic (RR > 30)

C. Moderate respiratory compromise (increased effort, gagging/retching)

D. Severe respiratory compromise (dyspnoea and cyanosis)

It should be noted that clinical signs will differ not only between patients, but can also vary significantly between cats and dogs affected by tick paralysis. Dr Gerardo Poli, Director at Animal Emergency Service and author of the MiniVet Guide, emphasises the importance in noting the differences in gait score and respiratory score between dogs and cats. While the severity of paralysis cases in dogs tends to be influenced primarily by the respiratory score, this is conversely noted in cats, where the gait score is often more indicative of the severity of paralysis (due to their lesser likelihood to regurgigate).

On review of over 2000 feline cases of tick paralysis, 90% of ticks were found from the shoulders forwards.

Dr Ellie Leister, Animal Emergency Australia, 2018

In some cases, a tick may be discovered by the owner, and a diagnosis can be made almost immediately based on clinical signs. But even if this is the case, a thorough veterinary assessment in any of these situations is vital. This allows the veterinarian and or veterinary nurse to discover the tick in question and any additional ticks on the patient.

Tick Paralysis Diagnostics

So, you’ve found an engorged paralysis tick and the patient is displaying typical clinical signs. Surely that’s diagnostic enough, right? It might not be obvious, but there are several additional diagnostic tests that should also be considered to maximise your chance of saving every tick patient:

1. Thoracic Radiographs

Aspiration pneumonia should be ruled out and is of concern in any patient with breathing difficulty, as Dr Gerardo Poli states that approximately 80% of patients presenting with tick paralysis have some degree of aspiration pneumonia. A 3-view thoracic radiograph series should be performed. The right middle lung lobe is the typical location for aspiration with an animal in sternal recumbency, though this can vary depending on if the animal was laterally recumbent.

2. Blood Gas

Venous sampling is recommended on arrival, which allows for interpretation of PCO2 (a measure of the patient’s ability to ventilate). Though an arterial sample is ideal, this adds a lot of stress and time to a patient that can’t surmount a stress response and may require less handling. If general anaesthesia or heavy sedation is required, then an arterial sample can be attempted. PaO2 and PaCO2 can be monitored and the need for oxygen supplementation, different sedation requirements or mechanical ventilation assessed.

PaO2 <60mmHg indicates severe hypoxemia requiring supplementation vs mechanical ventilation. A reduction in PaO2 can also indicate deterioration in lung function too (eg: aspiration pneumonia) and although this cannot be interpreted from a venous sample, an SPO2 of below 95% can be indicative of primary lung disease. Additionally, PaCO2 >60mmHg suggests inadequate ventilation, most likely from respiratory paralysis and mechanical ventilation is required. Be sure to also consider sedation if associated with excitement/stress.

3. Electrolytes

Some tick patients may have had significant vomiting or regurgitation prior to presentation, thus close monitoring of electrolytes on presentation can be incredibly useful. In these situations, loss of Na and K, and a metabolic alkalosis (loss of Cl- and H+ ions) maybe apparent. This will help to guide your fluid therapy based on each patient.

4. PCV/TS

Although a simple test that may be overlooked, performing a PCV/TS can be particularly useful in certain tick patients. This is often within normal range on presentation in most cases, though can be a useful indicator of dehydration if substantial vomiting/regurgitation has occurred. This must also be interpreted in combination with a thorough clinical exam, as dehydration is a physical examination finding and should not be made solely based on PCV/TS.

5. Entire Body Clipping

This is recommended highly in all cases of tick paralysis. In a recent study, 9% of cats with tick paralysis had a second tick identified. To prevent the continuing exposure to tick venom and ensuing paralysis requires removal of all ticks, it is imperative to perform a full clip. Naturally this can be highly stressful for patients already affected by tick paralysis, so perform under sedation (mainly for dogs), and general anaesthesia (for all cats) to reduce stress and control respiration.

One of the most common sites of missed ticks in patients that have been clipped is around the face. This means that “lion clips” (where hair is left around the face and head) should be avoided if possible. Despite performing a thorough tick clip, it is vital to repeat tick searches every 8 hours, as ticks that are still attached will grow in size and become easier to locate.

Now that we’ve got the clinical signs and diagnostics under control, take the time to explore our next article where we’ll dive into the most important part of the tick paralysis patient: treatment. We’ll also discuss the key points surrounding the most important component of treatment, TAS (tick antiserum), and how to dose and administer TAS appropriately for each patient.

Want to explore our completely free full Tick Paralysis Protocol that you can print off and quickly access in your clinic? Or maybe tune into our AEA Tick Panel Roadshow video? Sign up to VetAPedia and access 100+ clinical resources to enhance your emergency skills.

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