Neurological disease suspected to be caused by tick-borne encephalitis virus infection in 6 horses in Switzerland.
Authors: Magouras Ioannis, Schoster Angelika, Fouché Nathalie, Gerber Vinzenz, Groschup Martin H, Ziegler Ute, Fricker Raffael, Griot Christian, Vögtlin Andrea
Journal: Journal of veterinary internal medicine
Summary
Between 2011 and 2019, six horses in Switzerland presented with acute neurological disease characterised by ataxia and proprioceptive deficits, prompting investigation for tick-borne encephalitis virus (TBEV) infection in a region where human cases had been documented. Retrospective examination of clinical and microbiological data revealed that five horses tested positive for TBEV-specific IgM antibodies (laboratory unit values 30–56), with a sixth horse included based on borderline serology (LU 22.3) and clinical presentation consistent with transitional acute-to-chronic infection. All affected animals originated from TBEV-endemic areas of Switzerland where tick exposure was epidemiologically plausible. The findings underscore that whilst TBEV infection in horses remains rare, it warrants consideration as a differential diagnosis for acute neurological disease in endemic regions, particularly where human cases provide epidemiological context. Standardised diagnostic criteria for TBEV and related Flaviviruses in equine patients would substantially improve clinical decision-making and case identification, especially given the challenges of distinguishing acute infection from cross-reactive antibody responses in tick-exposed populations.
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Practical Takeaways
- •Include TBEV in your differential diagnosis list for horses presenting with acute neurologic signs (ataxia, proprioceptive deficits) if they are from or have travelled through endemic regions of Switzerland or other TBEV-endemic areas
- •Tick prevention and control measures are essential for horses in TBEV endemic regions, as the virus is transmitted by tick bites to multiple species including humans and horses
- •Request appropriate serological testing (virus neutralization test and TBEV-specific IgM antibodies) when neurologic disease is suspected in at-risk populations, as standardized diagnostic criteria are currently lacking
Key Findings
- •Six horses from TBEV endemic regions of Switzerland presented with acute neurologic disease (ataxia and proprioceptive deficits) between 2011 and 2019
- •All horses tested positive for TBEV via virus neutralization test, with 5 of 6 horses confirming TBEV-specific IgM antibodies (LU values 30-56)
- •All affected horses originated from areas where humans with confirmed tick-borne encephalitis had been bitten by ticks, suggesting geographic and epidemiologic association
- •Acute TBEV infection should be considered as a differential diagnosis in horses with neurologic signs from endemic areas, despite limited prior reports in equine medicine