Canine Tick-Borne Encephalitis: Clinical Features, Survival Rate and Neurological Sequelae: A Retrospective Study of 54 Cases (1999–2016)

Abstract

Tick-borne encephalitis (TBE) is one of the most important infectious diseases of the central nervous system in dogs from endemic areas. While in humans survival rate and long-term outcomes are well described, these data are lacking in veterinary literature. The aim of the present paper is to characterize the clinical aspects of TBE and to investigate fatality rate, long-term outcome and the long-term neurological sequelae in a population of dogs infected with TBE. We performed a retrospective analysis of 54 dogs diagnosed with TBE at the veterinary hospital of the University of Zurich between 1999 and 2016. Medical data such as signalment, clinical presentation, results of diagnostic procedures, treatment and outcome were collected and analyzed. Statistical analysis including a cox proportional hazard model using a backward stepwise regression approach was performed. In 62% of the TBE cases unspecific signs were described before the onset of neurological signs, resembling a biphasic appearance that is well known in human TBE. Case fatality rate was 33% and all dogs died within the first 4 months after diagnosis. Long-term neurological sequalae were detected in 17% of the TBE cases. For each day of clinical signs before hospital entry the odds of sequalae increased by a factor of 1.88 (CI 1.04–3.15). Older dogs and dogs presented with seizure activity had an increased hazard risk of death (Hazard ration = 1.2, p = 0.03; and 9.38, p = 0.001, respectively). In conclusion, despite TBE being a life-threatening disease with severe clinical signs, the survival rate in our study was 67%. However, long-term sequalae can be of concern especially in dogs with longer clinical course.

Suspected tick‐borne flavivirus meningoencephalomyelitis in dogs from the UK: six cases (2021)

“…Two dogs did not show lower motor neuron signs but presented generalised tonic seizures and abnormal behaviour. In the literature, symptomatic cases present a biphasic appearance with an initial unspecific period of pyrexia, anorexia and lethargy lasting a maximum of 10 days followed by the development of the neurological signs (Kaiser, 2008, 2012; Kleeb et al ., 2021; Pfeffer & Dobler, 2011; Riccardi et al ., 2019; Yoshii, 2019). Although no pathognomonic signs have been associated with TBEV infections, the presence of severe neck flaccidity has been previously described by Horger et al .…”

“…Tick‐borne encephalitis (TBE) is caused by a flavivirus – tick‐borne encephalitis virus (TBEV) – that is mainly transmitted via a tick bite, especially Ixodes ricinus and Dermacentor species (Bogovic & Strle, 2015; Kleeb et al ., 2021; Phipps & Johnson, 2022). Three different subtypes (European, Siberian and Far‐Eastern) have been described in Europe (Phipps & Johnson, 2022), and two recent subtypes (Baikalian and Himalayan) have been described in other parts of the world (Dai et al ., 2018).…”

“…Three different subtypes (European, Siberian and Far‐Eastern) have been described in Europe (Phipps & Johnson, 2022), and two recent subtypes (Baikalian and Himalayan) have been described in other parts of the world (Dai et al ., 2018). The European subtype has an important clinical incidence in Europe, where it presents as an endemic disease in both people and dogs (Bogovic & Strle, 2015; Kaiser, 2008, 2012; Kleeb et al ., 2021; Pfeffer & Dobler, 2011; Phipps & Johnson, 2022; Riccardi et al ., 2019; Salat et al ., 2021; Yoshii, 2019). Around 70% to 98% of human infections are asymptomatic (Kaiser, 2008) and only 20% of dogs present severe disease (Nygren et al ., 2022).…”

“…In both humans and animals, the symptomatic cases present a biphasic course, characterised by an initial phase with nonspecific signs such as pyrexia and lethargy followed by the development of severe neurological signs such as altered consciousness, seizures, lower motor neuron paresis or paralysis (especially within the thoracic limbs) and different cranial and spinal nerve dysfunction (Kaiser, 2008; Kleeb et al ., 2021; Riccardi et al ., 2019; Salat et al ., 2021; Yoshii, 2019). Epidemiologically, TBEV affects different species including humans, cattle, dogs, wildlife and small mammals, in which the virus can infect them as primary or reservoir hosts (Kaiser, 2008, 2012; Kleeb et al ., 2021; Pfeffer & Dobler, 2011; Phipps & Johnson, 2022; Riccardi et al ., 2019; Yoshii, 2019). Few clinical cases of TBE in dogs have been reported in non‐endemic areas such as areas of Southern Europe and Scandinavia (Andersson et al ., 2020; Pfeffer & Dobler, 2011; Weissenböck & Holzmann, 1997).…”

“…The incidence of human cases has been gradually increasing in the last decade (Pfeffer & Dobler, 2011; Riccardi et al ., 2019), reporting sequelae in 20% to 25% of the surviving human patients (Czupryna et al ., 2018; Nygren et al ., 2023), and a fatality rate of 2% (Bogovic & Strle, 2015). Scant information is available about survival and sequelae in dogs (Kleeb et al ., 2021).…”