Abstract
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 10(6) TCID50 or 10(3) 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.
Highlights
Visna/maedi virus (VMV) and caprine arthritis encephalitis virus (CAEV) are small ruminant lentiviruses (SRLV) that cause chronic progressive inflammatory disease in the lungs, brain, joints and mammary glands of sheep and goats (Haase, 1986)
To determine whether sheep can be infected via the ocular route, blood samples were taken at regular intervals after experimental infection of sheep via the conjunctival space Journal of General Virology 89
In sheep that received 106 tissue culture infectious dose 50 % (TCID50) VMV via the conjunctival space, the animals first became positive by seminested PCR (snPCR) at 4, 5 and 9 weeks post-infection
Summary
Visna/maedi virus (VMV) and caprine arthritis encephalitis virus (CAEV) are small ruminant lentiviruses (SRLV) that cause chronic progressive inflammatory disease in the lungs, brain, joints and mammary glands of sheep and goats (Haase, 1986). The main routes of infection are thought to be ingestion of colostrum or milk containing infected macrophages and/or free virus or via contact with respiratory aerosols It is known that alveolar macrophages are a target for infection (Gendelman et al, 1986) and it has been recently demonstrated that lung fluid from naturally infected sheep contains free virus at levels commensurate with efficient transmission via contact with respiratory secretions (McNeilly et al, 2007). It has been shown that infection via the distal lung tissues is very efficient compared with tracheal (McNeilly et al, 2007) or nasal tissues (Torsteinsdottir et al, 2003). The available information points to transmission between adult animals occurring through inhalation of aerosolized free virus and possibly aerosolized alveolar macrophages and subsequent infection of recipient alveolar macrophages or respiratory tract dendritic cells (Pepin et al, 1998)
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