Clinic and CNS pathology of natural Visna cases

Abstract

Summary Objective: This study summarizes the clinical, serological, pathomorphological and laboratory findings in 19 sheep with spontaneous Visna in Germany. The cases occurred over a period of 13 years in 13 flocks. In all affected sheep cytologic examination of cerebrospinal fluid (CSF) was performed. In addition in six flocks from which 12 of the Visna cases came the whole flock was tested for Maedi/Visna virus (MVV) antibodies. Material and methods: The diagnosis of spontaneous Visna with typical clinical signs was proven by serological and histopathological investigations. Serological screening for MVV antibodies was performed with the agargel-immuno- precipitation-test (AGIDT). Additionally, cerebrospinal fluid (CSF) was obtained by lumbosacral puncture and examined cytologically. Results: Nine of the 19 cases were Texels and six East Frisian Milk sheep. Six out of nine Texels came from the same flock with a MVV-antibody intra-flock prevalence of 0.94. The mean age of the sheep was 3.9 ± 2.3 years (0.5–10 years). Time between onset of clinical symptoms until euthanasia due to recumbency was 35 ± 23 days (6–102 days). In most cases clinical signs started with ataxia, staggering and circling, followed by increasing paresis of the hind legs. In the late stages of the disease 14 sheep suffered from tetraparesis. Trembling of lips or eye lids, blindness and scratching were rare signs. In all cases pleocytosis (11–876 M/l, mean = 167 M/l) with mononuclear cells, predominantly macrophages, was found. This finding provides an additional diagnostic aid to support the clinical differentiation from other infectious diseases with neurological manifestation in sheep. Histopathology of the CNS revealed in most cases a severe leukoencephalitis and demyelinisation with perivascular lymphocytic infiltration. Conclusion and clinical relevance: Visna is an important differential diagnosis in CNS disorders of sheep. It also occurs in animals younger than one year. Visna occurs especially in highly infected flocks of susceptible sheep breeds. CSF cytology can help to differentiate Visna from other CNS diseases. Clinically, Visna may be an important differential diagnosis to Scrapie.