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STAGING OF TICK PARALYSIS (in DOGS)

Staging the severity- general
Staging the severity- J Ilkiw's original classification
Staging the severity- Tick Paralysis Forum classification

Staging the severity- general

The concept of staging tick paralysis was originally insituted by Ilkiw et al (1987) for the purpose facilitating analysis of data in her later experiments. At least one serum manufacturer, however, (AVSL) has advocated using the staging classification in calculating the dose of tick antiserum to be used. Perhaps this protocol needs to be looked at again- for example would one, by comparison, give a smaller dose of snake antivenom simply because one is seeing milder signs when a case is presented early? Conversely, should one always assume that a full dose of toxin may have been injected and seek to neutralise that toxin load?

In clinical practice, staging is certainly useful in communicating information about prognosis and disease progression. However, there can be quite a degree of overlap in the parameters described in the various stages- so it is wise not to be dogmatic. In the original Ilkiw et al (1987) staging classification, affected animals were assigned to one of 5 categories. These are outlined below but with modifications based on clnical observations (see further below for Ilkiw's original experimental description ). The Illkiw and Turner classification has since been further refined at the Merial Tick Paralysis Forum (1988) to include subjective information about the effects on respiratory difficulty.

Stage 1 (weakness)

There is paresis (weakness) and real or apparent ataxia (stumbling, drunken appearance), more noticeable climbing stairs; there is a change in the character of the bark; dogs are still alert, eating and drinking normally; a dry cough is sometimes present; sometimes a short gag is heard at the end of the cough; some dogs may be anorexic (inappetant) and seem simply dull and lethargic, others are nervous and distressed; there is a fall in respiratory rate and plasma bicarbonate with a rise in expiratory time, although some dogs may be panting heavily.

Stage 2 (inability to walk)

The dog can recover from lateral recumbency (lying on it's side), crawl around the floor, wag its tail and appear alert; a few dogs will occasionally vomit but most can swallow normally; there is usually a slight change in the respiratory pattern with a more noticeable expiratory phase; both respiratory rate and arterial oxygen tension fall while there is a further rise in expiratory time; the alveolar-arterial oxygen tension difference rises.

Stage 3 (inability to right)

Dogs are unable to attain sternal recumbency (sit up on chest) despite making efforts to do so; limb withdrawal reflexes are present but are considerably dulled, being slower and weaker; pupils are normal or dilated but still responsive to light; the nictitiating membranes (third eyelids) protrude slightly; the gag reflex is depressed and saliva tends to pool under the dog's chin as it lies on the floor; a marked end-expiratory grunt is present; vomiting and retching are increased; the respiratory rate continues to fall; the minute respiratory volume also falls.

Stage 4 (no withdrawal reflexes)

There is still spontaneous movement in all limbs; limb withdrawal reflexes are slower and weaker; the pupils are usually dilated and the pupillary light reflex is absent in most cases; the nictitating membrane is halfway across the eye; there is an increase in saliva pooling; there is loss of bladder control and the development of a characteristic smell (urine in coat?); grunting respiration is marked; respiratory rate, minute respiratory volume, arterial oxygen tension, pH and standard bicarbonate fall significantly; expiratory time and alveolar-arterial oxygen tension difference rise significantly.

Stage 5 (moribund)

The dog is within 2-3 hours of death; all withdrawal reflexes have disappeared, the distal tail being the only area responding to pain stimulation; there is now marked pooling of saliva, the pupils are dilated, corneas are dry and the pupillary light reflexes are absent; the animal appears much more depressed and the legs move involuntarily with the respiratory effort; the lips are drawn back with each breath and the mucous membanes are grey; respiration becomes gasping and intermittent.

Staging the severity- J Ilkiw's original classification

Jan Ilkiw's original staging classification based on observations in 7 experimentally infected dogs (each infected with 3 or 4 unfed female adult paralysis ticks):

Stage I - paresis

The signs observed were firstly a change in character of the bark to a hoarse "husky" type and then a slight paresis of the hindlimbs. The dogs appeared alert, ate and drank normally and did not vomit. Coughing was observed in one dog. The character of respiration was normal.

Stage 2 - unable to walk

The dogs were in lateral recumbency, but could right themselves and hold this position if prompted. They crawled around the floor, were alert and responded by tail-wagging when approached. Withdrawal reflexes were present in all limbs when interdigital skin was pinched. There was no apparent central awareness of pain when the skin of the neck or forelimbs was pinched, but painful stimulation elsewhere resulted in movement and the dogs would look at that area. The pupils were normal in size and responsive to light. Although the gag reflex was diminished, the dogs appeared to be able to swallow, as no saliva was noticed to pool on the floor. Two dogs vomited during this stage; one vomited white frothy material, while the other vomited bile-stained material. Retching could be elicited if food was placed in front of some dogs. There was a slight change in respiratory pattern with respiration becoming more noticeable.

Stage 3 - unable to right

The dogs lay in lateral recumbency and despite attempts to right themselves were unable to do so. Withdrawal reflexes were usually present in all limbs, but were slower and weaker. There was no response to a painful stimulus to the neck, between the scapulae and along the forelimbs. The pupils were normal to dilated, but responsive to light. The nictitating membranes were half-way across the eyes. The gag reflex was depressed and saliva pooled on the floor in front of the dogs. Respiration was of a "grunting" type with forced expiration.

Stage 4 - unable to right and lacking limb withdrawal reflexes

There were spontaneous movements of all limbs, although no response was observed to painful stimulation on the neck, thorax, forelimbs, and down the hindlimbs. Painful stimulus to the abdomen or the tail caused attempts at movement. In most dogs the pupils were dilated, the pupillary light reflex was absent in some cases and the nictitating membrane more than half-way across the eye. The gag reflex was depressed and pooling of saliva on the floor in front of the dogs was marked. There appeared to be loss of bladder control with urinary incontinence. Respiration was forced and "grunting" in type.

Stage 5 - moribund

These dogs were within 2 h of death. All withdrawal reflexes had disappeared and the distal half of the tail was the only area which responded with movement to a painful stimulus. The gag reflex was depressed and there was marked pooling of saliva on the floor in front of the dogs. The pupils were dilated and pupillary light reflexes were absent. Respiration was forced and "grunting", the dogs appeared agitated and the limbs seemed to move with respiration. As this stage progressed, the lips were drawn back with each breath and the colour of the mucous membranes appeared grey. Respiration then became gasping and intermittent. The pupils were widely dilated and the corneas dry.

Staging the severity- Tick Paralysis Forum classification

The staging method proposed by the Merial Tick Paralysis Forum (1988), based on the method of Dr Ross Sillar is as follows:

In this sytem greater importance is placed on respiratory compromise. A dog classed as a 2D may have a poorer prognosis and warrant more aggressive therapy* than one classed as 3B.

[*you might ask as to what therapy this specifically entails- more antiserum??, but see discussion on whether we should be dosing maximally in the early stages anyway]

References:

Ilkiw J E, Turner D M, Howlett C R, Goodman A N: Infestation in the Dog by the Paralysis Tick, Ixodes holocyclus. Parts 1, 2, 3, 4, 5. Australian Veterinary Journal, 65:8, 1988.

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