The sudden death of Diallo BB, a top grand prix dressage horse owned by German Olympian Jessica von Bredow-Werndl, has drawn attention to equine Borna disease virus, though the virus was later ruled out as the cause. The 11-year-old Hanoverian gelding's illness remains unexplained, prompting interest in the rare neurotropic virus primarily affecting Central Europe. With fatality rates of 80 to 100 percent in horses, the disease underscores ongoing veterinary challenges.
Diallo BB's death has reignited discussions about equine Borna disease virus (BDV), also known as Borna disease virus 1 (BoDV-1), a pathogen that targets the central nervous system of horses and other mammals. First documented in the late 19th century after a major outbreak in 1885 among cavalry horses in Saxony, Germany—near the town of Borna from which it takes its name—the virus causes progressive neurological disorders. Early symptoms in horses include subtle behavioral changes like anxiety or reduced responsiveness, escalating to ataxia, head pressing, circling, impaired vision, tremors, muscle weakness, difficulty swallowing, and seizures in advanced stages.
Transmission occurs through exposure to contaminated bodily fluids, saliva, or excretions from small mammals such as the bicolored white-toothed shrew, which act as reservoirs. There is no evidence of direct horse-to-horse spread under normal conditions, with infections typically resulting from wildlife spillover. The disease is most prevalent in Central Europe, including Germany, Switzerland, Austria, and Liechtenstein, where most equine cases are recorded. Sporadic infections have been noted in other species, and rare human cases of severe encephalitis have emerged in Germany over the past decade, though no horse-to-human transmission is confirmed.
No specific antiviral treatment exists for BoDV-1 in horses; care is limited to supportive measures like hydration, nutrition, anti-inflammatories, and seizure control. Once symptoms appear, the prognosis is poor, with historical fatality rates ranging from 80 to 100 percent, and survivors often facing lasting neurological deficits. For imports to North America from affected regions, regulations require health certifications confirming no recent exposure on premises with reported cases, alongside physical inspections, but BoDV-1 testing is not mandatory.
Ongoing research focuses on viral reservoirs, transmission routes, and potential antivirals to mitigate risks to equine health and address zoonotic concerns.
