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

The weather determined how 'hot' the tick paralysis season was in eastern Australia: 2018-2024

The eastern paralysis tick, Ixodes holocyclus, is a tick of much veterinary importance in Australia. Each year, thousands of dogs and cats present to veterinary clinics and hospitals with signs of tick paralysis. In a previous paper, we constructed two models to explain prevalence and temporal distributions of tick paralysis cases presenting to emergency veterinary hospitals in South East Queensland (2009-2020) and the Northern Beaches of Sydney (1999-2017). The first model accounted for the intensity of the clinical burden of tick paralysis based on the prevalence of cases of tick paralysis in the tick paralysis season whereas the second model accounted for the start of the tick paralysis season. In the present paper, we test our models further, with much additional data from 2021 to 2023 (South East Queensland) and from 2018 to 2023 (Northern Beaches of Sydney). During the defined tick paralysis season in these locations, 10.3 % (3207 of 31,217) of veterinary-consultations were for tick paralysis. On average, predictions for the prevalence of cases of tick paralysis were 1.3 % (0.013) away from the actual prevalence whereas predictions for the start of the tick paralysis season were 1.7 weeks away from the actual start of the season. The prediction of the prevalence of tick paralysis cases was most accurate for Brisbane and least accurate for the Northern Beaches of Sydney whereas, curiously, the prediction for the start of the tick paralysis season was most accurate for the Northern Beaches of Sydney and least accurate for Brisbane. We re-fitted the models with the new data. We predict that about 10 % (Sunshine Coast), 5 % (Brisbane), 7 % (Gold Coast) and 12 % (Northern Beaches of Sydney) of veterinary-consultations in the tick paralysis season of 2024 will be cases of tick paralysis, resulting in a tick paralysis clinical burden intensity of similar magnitude to previous years. Such predictions allow for timely public education campaigns around the importance of prevention and appropriate resource planning for veterinary clinics.

The geographic limits and life history of the tropical brown dog tick, Rhipicephalus linnaei (Audouin, 1826), in Australia with notes on the spread of Ehrlichia canis

The tropical brown dog tick, Rhipicephalus linnaei, is a tick of much medical, veterinary, and zoonotic importance. This tick has a nearly world-wide distribution due to its ability to survive and propagate in kennels and houses. Rhipicephalus linnaei is the vector of Ehrlichia canis, the causative agent of canine monocytic ehrlichiosis, an often debilitating disease of canids and, occasionally, humans. To prevent incursion of E. canis into Australia, dogs entering Australia have been required to have a negative immunofluorescence antibody test for E. canis. In May 2020 however, E. canis was detected in Western Australia. The detection of E. canis in Australia prompted disease investigation and concerted surveillance for R. linnaei and E. canis in regions across Australia. These investigations revealed that R. linnaei was established far beyond the previously recognised geographic range limits of this tick. In the present paper, using records from various collections, published data, and data from our network of veterinarian collaborators and colleagues, we update the current geographic range of R. linnaei in Australia. Our analyses revealed that the geographic range of R. linnaei in Australia is much wider than was previously supposed, particularly in Western Australia, and in South Australia. We also map, for the first time, where E. canis has been detected in Australia. Last, we discuss the possible routes of incursion and subsequently the factors which may have aided the spread of E. canis in Australia which led to the establishment of this pathogen in Australia.

Apparent tick paralysis by Otobius megnini in a cat

In this study, we report a rare case of tick paralysis in a cat induced by Otobius megnini infestation. An 11-month-old female cat was admitted to a private veterinary clinic in Luling Texas, USA presenting with depression, tachycardia, and flaccid paralysis of the entire body. The four recovered ticks were morphologically and molecularly identified as O. megnini nymphs. Following initial tick removal and treatment with 0.1% milbemycin oxime in the ear canal on the first day of hospitalization, and additional tick removal and topical selamectin treatment on the second day of hospitalization the animal gradually improved. The recovery of the cat after tick removal supports the diagnosis of tick toxicosis. While tick antiserum is not available in North America, prevention of tick infestation and tick-induced paralysis can be effectively accomplished using repellent collars and the compliant use of other ectoparasiticide products year-round.

The weather determines the number of cases of tick paralysis in dogs and cats in eastern Australia, caused by Ixodes holocyclus, the eastern paralysis tick

We studied over 222,000 cases of emergency veterinary consultations in four regions along the eastern coast of Australia. We found that cases of tick paralysis (TP) caused by the eastern paralysis tick, Ixodes holocyclus, accounted for 7.5% of these cases: >16,000 cases. The season of TP and the number (prevalence) of TP cases varied among regions and over the years. Our study of the association between weather and (i) the start of the season of TP, and (ii) the number of TP cases revealed much about the intricate relationship between the weather and I. holocyclus. We studied the effect of the hypothetical availability of isoxazoline-containing tick-preventative medicines and found that an increase in the availability of these medicines had significantly contributed to the decrease in TP cases. We found that the weather in winter accounted for the time of the year the season of TP starts whereas the weather in summer accounted for the number of TP cases in the TP season. Last, through a study of the effects of shifts in the climate under four hypothetical scenarios (warmer/cooler and drier/wetter than average), we propose that the start of the season of TP depends on how soon the weather in winter becomes suitable for the activity (e.g. host-seeking) and the development of I. holocyclus nymphs, and that the number of TP cases during the TP season depends on how many engorged female ticks and their eggs survive during summer.