Management of respiratory failure from tick paralysis

Static anisocoria in cats and dogs with naturally occurring tick paralysis (Ixodes holocyclus)

OBJECTIVE

To characterise the novel occurrence and neuro-ophthalmological features of static anisocoria in cats and dogs with tick paralysis (TP) (Ixodes holocyclus) due to a single tick located remote from the head and neck.

DESIGN

Observational case series with retrospective analysis.

METHODS

Medical records were reviewed from 69 cats and 169 dogs treated for TP from a suburban veterinary hospital in Newcastle, New South Whales, between September 2005 and October 2021.

RESULTS

Anisocoria was observed in 2/18 (11.1%) cats and 3/30 (10.0%) dogs with a single tick located remote from the head and neck. These proportions were not different when compared within species to 4 of 28 (14.3%) cats and 16 of 98 (16.3%) dogs with aniscocoria with a single tick located on the head and neck region (P = 1 and 0.56 respectively). Anisocoria arose from pupillary efferent dysfunction and included unilateral oculoparasympathetic dysfunction (internal ophthalmoplegia) in one dog, unilateral oculosympathetic dysfunction (Horner's syndrome) in one cat and one dog, and a combination of bilateral, but asymmetric, oculosympathetic and oculoparasympathetic dysfunction in one cat and one dog.

CONCLUSION

It is proposed that anisocoria in cases of TP with a tick located remote from the head and neck is due to an intrinsic latent asymmetry in the safety factor for pupillary efferent function that is unmasked by a systemically distributed holocyclotoxin inhibiting neural transmission within this system, and this is the prevailing pathomechanism, rather than a direct local effect, underscoring anisocoria with a tick located on the head or neck.

Mechanical ventilation in dogs and cats with tick paralysis

Respiratory failure from tick paralysis (TP) is an important cause of mortality in cats and dogs in Australia, occurring from a combination of respiratory muscle paralysis, upper respiratory tract obstruction and pulmonary disease. Patients may require positive-pressure ventilation in management of any combination of hypoxemia, hypoventilation or respiratory fatigue, but may also require airway management due to laryngeal paralysis. No single ventilation strategy is recommended due to the heterogenous disease presentations. Lung protective ventilation should be used in patients with pulmonary disease. Due to local and systemic effects of TP, patients are at higher risk of complications such as aspiration pneumonia and corneal ulceration and may have additional intravenous fluid and nutritional considerations. Treatment with hyperimmune serum is associated with improved outcomes. Prognosis is considered good with documented survival to discharge (STD) of 52.6-77% for animals with TP ventilated with lung disease and 90.5% for animals without lung disease. Median reported duration of ventilation for TP ranges from 23 to 48 h (range 3 h-10 days). The severity of individual neuromuscular signs and the presence of associated conditions such as aspiration pneumonia and laryngeal paralysis may necessitate longer periods of mechanical ventilation. This review aims to summarize the current recommendations regarding indications, management and prognosis of cats and dogs undergoing MV for TP and to identify areas for future research.

Positive Airway Cultures in Dogs and Cats Receiving Mechanical Ventilation for Tick Paralysis

Animals with tick paralysis often require mechanical ventilation (MV) but previous publications have identified knowledge gaps regarding the development of bacterial pneumonia, and the specific pathogens involved. The objectives of this study were to describe the clinical course and culture and susceptibility profiles of bacteria isolated from airway samples of dogs and cats mechanically ventilated for tick paralysis that had positive airway cultures. Medical records were reviewed, and cases included if they had a positive airway sample culture during MV for tick paralysis. Twenty-four dogs and two cats were included. Most (85%) received empirical antimicrobials before airway sampling. The most common organisms isolated included Staphylococcus spp. (11), Klebsiella spp. (9), Enterococcus faecalis (8), Escherichia coli (6), Enterococcus faecium (3), Pseudomonas aeruginosa (4), and Mycoplasma spp. (3). Evidence of aspiration pneumonia was present in 22/25 (88%) cases that had thoracic radiographs performed. Seventy-seven percent of cases received antimicrobials to which the cultured bacteria were susceptible during hospitalisation. The median duration of MV was 4 days (range 1-10). Most (77%) survived to discharge, 19% were euthanised, and one died. In a multivariable logistic regression analysis it was identified that selection of antimicrobials to which the causative bacteria are susceptible was associated with survival to discharge (Odds ratio 45.8, p = 0.014; 95%CI 1.98-14,808), as was length of MV, with every day an animal is ventilated associated with a 4.7 times increased chance of survival (p = 0.015; 95% CI 1.21-78.4).

Elective cricothyrotomy in a dog with transient laryngeal paralysis secondary to Australian paralysis tick (Ixodes holocyclus) envenomation

The tube cricothyrotomy (CTT) has recently been introduced to small animal medicine as a viable surgical airway access procedure; however, there are no reports documenting its clinical use. The author's objective is to describe the clinical application, complications, and management of an elective CTT in a dog. Furthermore, the characteristics of CTT that may be clinically advantageous over temporary tube tracheostomy (TT) will be discussed. A 2‐year‐old female spayed German shepherd dog required mechanical ventilation (MV) due to unsustainable work of breathing as a result of tick paralysis and aspiration pneumonia. After successful weaning from MV, the dog was diagnosed with laryngeal paralysis. A surgical airway was performed using CTT to allow extubation and patient management whilst conscious. Complications included frequent tube suctioning due to accumulation of airway secretions in the tube and a single dislodgement event. The dog made an uneventful recovery with complete stoma healing by the second intention within 15 days. To the authors' knowledge, this is the first clinical report of an elective CTT performed to successfully manage upper airway obstruction in the dog. Its efficacy, clinical management and patient outcome are described.

Tick paralysis in dogs and cats in Australia: treatment and prevention deliverables from 100 years of research

This review of tick paralysis caused by Ixodes holocyclus in Australia addresses the question: What are the key discoveries that have enabled effective treatment and prevention of tick paralysis in dogs and cats? Critical examination of 100 years of literature reveals that arguably only three achievements have advanced treatment and prevention of tick paralysis in animals. First, the most significant treatment advance was the commercial availability of tick antiserum in the 1930s. Hyperimmune serum currently remains the only specific anti-paralysis tick therapy available to veterinarians in Australia. Second, advances in veterinary critical care have increased survival rates of the most severely affected dogs and cats. Critical care advancements have been enabled through specialised veterinary hospitals that can provide appropriate care 24 h a day, and advanced training of veterinarians, veterinary nurses and technicians. Third, perhaps that biggest advance of all in the last 100 years of research has been the commercial availability of the isooxazoline class of acaricidal preventatives in Australia specifically for I. holocyclus. This highly effective class of preventatives offers long duration of action, low cost, spot-on or oral formulations and a low rate of adverse reactions. Animal owners and veterinarians now have the most useful tool of all - a reliable preventative. This review reveals the key events in research over the last 100 years and the tortuous pathway to delivering better treatment and preventative options for this enigmatic Australian parasite.

Severe neurotoxicity requiring mechanical ventilation in a dog envenomed by a red-bellied black snake (Pseudechis porphyriacus) and successful treatment with an experimental bivalent whole equine IgG antivenom

Snakebite in dogs from Pseudechis porphyriacus (red-bellied black snake; RBBS) is a common envenomation treated by veterinarians in Australia where this snake occurs. This case report describes the successful treatment of a clinically severe RBBS envenomation in a dog with an experimental bivalent equine whole IgG antivenom and mechanical ventilation, following its presentation in a cyanotic state. The cause of the cyanosis and respiratory distress was considered due to paralysis from neurotoxins in RBBS venom. The dog was treated with two vials of bivalent antivenom, each containing sufficient antivenom to neutralise the lethal effects of 40 mg of tiger snake (Notechis sp) and 40 mg of brown snake (Pseudonaja sp) venom. Hypoxaemia (Sp0₂ of 75%) and hypercapnia (PaCO₂ of 61 mmHg) indicated the need for mechanical ventilation (MV) to prevent imminent death. The dog was anaesthetised using total intravenous anaesthesia and MV used for 18 h. Following discontinuation of MV, it resumed spontaneous breathing thereafter and made a complete recovery. Serum biochemistry revealed a significant myopathy with elevated CK and AST levels, peaking approximately 48 h post-treatment. Elevated liver enzymes, suggestive of hypoxic liver injury, were detected during the period of hospitalisation. The dog represented approximately one week after hospital discharge because of inappetence and mild hepatopathy, which resolved spontaneously by 30 d post-treatment. A mild coagulopathy was initially present which resolved within 24 h following antivenom treatment. At initial presentation, RBBS venom antigen was detected by sandwich ELISA in urine and serum. Free RBBS venom antigen was not detected post-antivenom treatment. Human cases of RBBS requiring ventilatory support are rare. This unusual case of RBBS envenomation in a dog highlights its potential clinical severity in dogs, and the need for early, aggressive, MV to achieve a successful outcome in cyanosed and clinically severe cases.

Acute lower motor neuron tetraparesis

Flaccid nonambulatory tetraparesis or tetraplegia is an infrequent neurologic presentation; it is characteristic of neuromuscular disease (lower motor neuron [LMN] disease) rather than spinal cord disease. Paresis beginning in the pelvic limbs and progressing to the thoracic limbs resulting in flaccid tetraparesis or tetraplegia within 24 to 72 hours is a common presentation of peripheral nerve or neuromuscular junction disease. Complete body flaccidity develops with severe decrease or complete loss of spinal reflexes in pelvic and thoracic limbs. Animals with acute generalized LMN tetraparesis commonly show severe motor dysfunction in all limbs and severe generalized weakness in all muscles.