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Experimental infection of sheep with visna/maedi virus via the conjunctival space

Heide Niesalla

Tom N. McNeilly

Division of Veterinary Biomedical Sciences, College of Medicine and Veterinary Medicine, University of Edinburgh, Summerhall, Edinburgh EH9 1QH, UK

Correspondence
Gordon D. Harkiss
gordon.harkiss{at}ed.ac.uk

Experiments were performed to determine whether visna/maedi virus (VMV), a small ruminant lentivirus (SRLV), could infect sheep via ocular tissues. The EV1 strain of VMV was administered into the conjunctival space of uninfected sheep, and the animals monitored for the presence of provirus DNA and anti-VMV antibodies in blood. The results showed that provirus DNA appeared in peripheral blood mononuclear cells of all animals within a few weeks of receiving either 10⁶ TCID₅₀ or 10³ TCID₅₀ of VMV. Of the animals receiving the higher dose of virus via the conjunctival space, two seroconverted by 7 and 10 weeks post-infection, one seroconverted 8 months post-infection, and one had not seroconverted by 15 months post-infection. With the lower virus dose, the animals infected via the trachea seroconverted by 4 and 14 weeks, respectively. After ocular infection with this dose, one animal showed a transitory seroconversion with low levels of antibody, peaking at 2 weeks post-administration. The remaining three of the animals infected via the eyes did not seroconvert over a period of 13 months. At post-mortem, evidence for the presence of proviral DNA was obtained from ocular tissue, lungs or mediastinal lymph node in both groups of animals. Histological analysis of lung tissue from animals receiving the lower dose of virus showed the presence of early inflammatory lesions. The results thus show for the first time that transmission of VMV can occur via ocular tissues, suggesting that the conjunctival space may be an additional route of natural transmission.

Published online ahead of print on 11 March 2008 as DOI 10.1099/vir.0.2008/000133-0.

Present address: Institute of Biotechnology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QT, UK.

Present address: Division of Parasitology, Moredun Research Institute, Pentlands Science Park, Penicuik, Midlothian EH26 0PZ, UK.