Visna in a UK flock and the biosecurity risk arising from the onward sale of likely infected pedigree stock

Small Ruminant Lentivirus infections in sheep most commonly present with respiratory signs (maedi) and indurative mastitis, while primary neurological signs (visna) have rarely been reported in Great Britain. Most reports of visna describe signs referable to myelitis, although central signs associated with encephalitis may feature. In this case, visna was diagnosed in a 4-year-old ewe in a small pedigree sheep flock, recently imported to GB from northern Europe. Initial clinical findings were of a head tilt, circling, facial tremors and a unilaterally reduced menace response. These neurological signs progressed to include hyperaesthesia, ipsilateral hemiparesis and recumbency. Flock level infection had recently been diagnosed by serology, and the diagnosis in this individual case was confirmed by serology and histopathology. The subsequent sale of animals from the flock through a large national auction and at private sales raises significant ethical questions and serves as a reminder of the importance of biosecurity precautions.