Acta Neuropathologica

, Volume 57, Issue 2–3, pp 171–178 | Cite as

Primary demyelination in visna

An ultrastructural study of Icelandic sheep with clinical signs following experimental infection
  • G. Georgsson
  • J. R. Martin
  • J. Klein
  • P. A. Pálsson
  • N. Nathanson
  • G. Pétursson
Original Works


Two Icelandic sheep with clinical signs of visna appearing 6–7 years after intracerebral infection with visna virus were killed, fixed by perfusion and the central nervous system lesions examined by light and electron microscopy. Both sheep showed similar pathological changes. In the brain there was a severe periventricular inflammatory process with small foci of liquefaction necrosis and scattered small granulomas. In some areas of inflammation there was evidence of primary demyelination but it was not prominent. In the spinal cord there were focal plaques of primary demyelination. At the ultrastructural level the spinal cord lesions showed unambiguous primary demyelination with many naked axons; various stages of remyelination with peripheral type of myelin were also common.

These observations indicate that the CNS lesions of visna, as seen in Icelandic sheep, fall into two categories: (a) an inflammatory process which often begins within weeks of infection and which occurs in the majority of infected animals in the absence of clinical paresis; and (b) focal demyelinating lesions of the spinal cord which are seen in sheep with clinical paresis but are uncommon in animals prior to onset of clinical signs. Both types of lesions may coexist.

Key words

Visna Retrovirus Primary demyelination Persistent infection Multiple sclerosis 


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Copyright information

© Springer-Verlag 1982

Authors and Affiliations

  • G. Georgsson
    • 1
  • J. R. Martin
    • 2
  • J. Klein
    • 3
  • P. A. Pálsson
    • 1
  • N. Nathanson
    • 3
  • G. Pétursson
    • 1
  1. 1.Institute for Experimental PathologyUniversity of IcelandReykjavíkIceland
  2. 2.National Institute of Neurological and Communicative Diseases and StrokeNIHBethesdaUSA
  3. 3.Department of Microbiology, School of MedicineUniversity of PennsylvaniaPhiladelphiaUSA

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