Leister E, Morton J, Atwell R, Webster R. Clinical presentations, treatments and risk factors for mortality in cats with tick paralysis caused by Ixodes holocyclus: 2077 cases (2008-2016). J Feline Med Surg. 2018 Jun;20(6):465-478.
Tick paralysis is a disease seen most commonly in Australia and is associated with the bite of the paralysis tick, Ixodes holocyclus (though a similar condition exists in North America caused by Dermacentor spp). It is a non-infectious disease caused by a toxin in tick saliva that causes an acute, progressive, ascending lower motor neuron paralysis. The disease in cats is different from dogs. In dogs, gait changes and weakness are the most common early signs of disease, however in cats respiratory changes such as laryngeal paralysis may occur first. Though often seen as a disease of dogs, this is also well recognized in feline medicine. Despite its occurrence in cats, there is little data on the prevalence, risks factors, treatment options, prognosis, and outcomes for this condition in cats.
The purpose of this study was to provide a description of tick paralysis in cats in Australia. It was designed as a retrospective single cohort study of cats presenting to four veterinary clinics in Queensland, Australia from 2008 to 2016. Cats were included if one or more ticks or tick craters were found on a cat with lower motor neuron or respiratory signs. 2213 cases were identified of which 2077 met all inclusion criteria. 1976 cats presented a single time, 46 cats presented twice, and 3 cats presented three times.
Breed, age, sex, vital signs, number of ticks/craters, and gait and respiratory scores were recorded for all cats on admission. Cats were stratified into two groups based on whether or not they received tick antiserum.
Case management was left to clinician discretion but generally included: Triage, sedation and oxygen administration, intravenous fluids, tick anti-serum (with or without pre-emptive steroids, antihistamines, etc), nursing care, coat clipping, and mechanical ventilation (if needed).
Outcomes were divided into: died or euthanized; discharged after resolution; discharged against medical advice; transferred to regular clinic; transferred to a specialist. Deaths were categorized into: died; euthanized based on cost; euthanized based on prognosis.
Number of cases increased in the autumn, decreased in summer, and spiked in the spring. Most cases occurred in the spring. Odds of mortality did not change based on month, season, or year; though percentage of cases that died by day 5 were slightly lower later in the study period.
Mortality status was obtained for 84% of cases. Of these, 3% died by day five of therapy (27 died at the presenting clinic, three were euthanized due to poor prognosis, 11 died at home after discharge against veterinary advice and 13 died at referring clinics after discharge). If only cases that received recommended treatment were included, risk of death was 2%. Most animals that died did so as a result of respiratory failure.
Factors that increased the chance of survival included:
- Clipping the coat
- Presenting gait score and respiratory score
- Normothermia on presentation
- Receiving Tick Anti-Serum (Not receiving TAS had a 8-13x odds ratio of death)
- Mechanical ventilation (if recommended)
- Not having a reaction to TAS
Despite cats with a reaction to TS having a higher mortality, overall there was a significant benefit seen to administering TAS. However, if mild and non-progressive signs are seen, the authors suggest it may be best to withhold antiserum.
Overall the authors describe a relatively high survival rate for cats with tick paralysis. They determined several risk factors for death (high gait and respiration scores, low body temperature, etc) and some treatment factors that can improve survival (i.e. clipping the coat and administration of tick anti serum). (MRK)