Two seasons of tick paralysis in Victoria yet one season in Queensland and New South Wales, Australia

We studied 22,840 cases of tick paralysis in dogs and cats that were attributable to infestation with the eastern paralysis tick, Ixodes holocyclus. We report that the mortality rates from the holocyclotoxins of the tick or from euthanasia due to complications arising from tick paralysis in dogs and cats were 10% and 8%, respectively. The distribution of cases of tick paralysis among the 52 weeks of 22 years (1999 to 2020, inclusive) in four regions along the eastern coast of Australia revealed much about how the life-cycle of this tick varied among regions. The four regions in our study were: (i) Cairns, Innisfail, and surrounding postcodes in Far North Queensland; (ii) South East Queensland; (iii) Northern Beaches of Sydney in New South Wales; and (iv) the Shire of East Gippsland in Victoria. We found that the season of tick paralysis started earlier in more northerly latitudes than in more southerly latitudes. We also found that Victoria has two seasons of tick paralysis, one from approximately the third week of February to the first week of May, and another from approximately the third week of September to the third week of December, whereas all of the other regions we studied in eastern Australia only had one season of tick paralysis. When we studied the two seasons of tick paralysis in Victoria, we found a statistically significant negative correlation between the number of cases of tick paralysis between the two seasons: the more cases in one season, the fewer the cases in the next season. One possible explanation for the negative correlation may be immunity to I. holocyclus acquired by dogs and cats in the first season.C) 2022 Published by Elsevier Ltd on behalf of Australian Society for Parasitology.

Automated summary

We conducted a study on 22,840 cases of tick paralysis in dogs and cats caused by the Eastern paralysis tick, Ixodes holocyclus. The mortality rates were found to be 10% and 8% for dogs and cats, respectively, due to the toxins of the tick or euthanasia associated with complications. Our study on the distribution of tick paralysis cases in four regions along the eastern coast of Australia revealed variations in the life-cycle of the tick among regions and differences in the timing of tick paralysis season between more northerly and southerly latitudes. Victoria was found to have two tick paralysis seasons, while the other regions had only one season.