A final diagnosis in a horse with clinical signs of encephalopathy can be challenging despite the use of extensive diagnostics. Clinical signs are often not pathognomonic and need to be interpreted in combination with (specific) laboratory results and epidemiological data of the geographical region of the origin of the case(s). Here we describe the diagnostic pathway of tick-borne encephalitis virus infection in two horses using established molecular diagnostic methods and a novel in situ hybridization technique to differentiate between regionally important/emerging diseases for central Europe: (i) hepatoencephalopathy, (ii) Borna disease virus, and (iii) West Nile virus infections.

This case report concerns a 1-day-old, full-term Quarter Horse colt presented due to a progressive inability to rise and nurse. Besides the general weakness, a marked bradycardia was evident, which was caused by a third-degree atrioventricular (AV) block. Subsequently, the diagnosis of acute nutritional myodegeneration (NMD) was made based on clinical signs, elevated muscle enzymes, ECG findings, as well as low serum selenium and vitamin E values. Despite intensive care and supportive therapy, the foal´s condition deteriorated, and euthanasia was elected. Necropsy confirmed the diagnosis of NMD and revealed diffuse necrosis and inflammatory infiltration of the skeletal and myocardial musculature, as well as the cardiac conduction system which might have resulted in complete AV block.

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