Study of compartmentalization in the visna clinical form of small ruminant lentivirus infection in sheep

Eight Visna (neurologically) affected sheep of the outbreak were used. Of the 350 clones obtained after PCR amplification, 142 corresponded to CNS samples (spinal cord and choroid plexus) and the remaining to mammary gland, blood cells, bronchoalveolar lavage cells and/or lung. The diversity of the env sequences from CNS was 11.1-16.1% between animals and 0.35-11.6% within each animal, except in one animal presenting two sequence types (30% diversity) in the CNS (one grouping with those of the outbreak), indicative of CNS virus sequence heterogeneity. Outbreak sequences were of genotype A, clustering per animal and compartmentalizing in the animal tissues. No CNS specific signature patterns were found.Bayesian approach inferences suggested that proviruses from broncoalveolar lavage cells and peripheral blood mononuclear cells represented the common ancestors (infecting viruses) in the animal and that neuroinvasion in the outbreak involved microevolution after initial infection with an A-type strain. This study demonstrates virus compartmentalization in the CNS and other body tissues in sheep presenting the neurological form of SRLV infection.Small ruminant lentiviruses (SRLVs) cause arthritis, mastitis, interstitial pneumonia (Maedi) and leukoencephalitis (Visna) in sheep and goats [1]. The clinical form Visna in sheep was first described in Iceland during the Visna Maedi Virus (VMV) epidemic in the first half of the last century [2]. From then, this neurologic form has been reported only sporadically [3-5]. However, in the last few years, the neurological form of SRLV disease has been diagnosed in numerous sheep of North-Western Spain, causing production losses [6]. In this outbreak, clinical signs usually appear at 1-2 years of age, but have been detected in animals as young as 4 months [7]. However, in other geographic areas of the world, Visna appears in animals over 2 years of age [2,8]. Also, in the animals affected by Visna within the outbreak, lesions freque