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

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 TCID 50 or 10 3 TCID 50 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. INTRODUCTIONVisna/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). Lymphoid tissue hyperplasia is also a feature, and more rarely lesions can be found in other tissues such as the kidneys, liver and heart (Georgsson & Palsson, 1971;Brellou et al., 2007). Recently, evidence for involvement of ocular tissues has been provided in natural cases of VMV infection (Capucchio et al., 2003).The SRLV show a distinct tropism for cells of the monocytemacrophage lineage and hence target organs rich in these cell types (Narayan et al., 1982;Gendelman et al., 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 (Cutlip et al., 1985;Adams et al., 1983;Palsson, 1976). 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 also been shown that infection via the distal lung tissues is very efficient compared with tracheal (McNeilly et al., 2007) or nasal tissues (Torsteinsdó ttir et al., 2003). The available information ...

Maedi in slaughtered sheep: A pathology and polymerase chain reaction study in southwestern Iran

“…In addition, the flock should also be tested for MVV, and seronegative and seropositive sheep should be isolated from each other. Aerosol transmission through respiratory tract and experimentally via ocular tissue is another route of viral transmission (Peterhans et al 2004;McNeilly et al 2007;Niesalla et al 2008). Complete eradication of the infection will be possible when detailed information on the genetic characteristics (in many geographical regions) of infected flocks and individual animals become available.…”

Small Ruminant Lentiviruses and Human Immunodeficiency Virus: Cousins that Take a Long View

“…The susceptibility of the latter to infection shows a gradation with nasal transmission being the least efficient followed by the trachea then the lower lung [97,99]. Recently, infection via conjuctival tissues has been demonstrated experimentally with an efficiency estimated to be intermediate between tracheal and lower lung infection [100]. This suggests that respiratory aerosols generated by coughing may transmit infection via a conjunctival route.…”

“…Viral DNA and antigen were detected in affected eyelids. Recently, it was shown that infection and inflammatory disease in conjunctival tissue can be induced experimentally in sheep [100]. No equivalent conjunctivitis has been described in HIV infections to date, despite the presence of virus in tears and conjunctival cells [103].…”

Small Ruminant Lentiviruses in Sheep: Pathology and Tropism of 2 Strains Using the Bone Marrow Route

“…15 Successful experimental infections with SRLVs have been performed using viral strains isolated from natural field infections 25,48 using different inoculation routes such as intravenous, intratracheal, intracerebral, intra-articular, or conjunctival. 25,32,40 However, more studies are needed to evaluate tissue/organ tropism upon experimental infection with SRLVs to enhance our understanding of the pathogenesis of the different clinical forms. The main objective of this work was to study comparatively the tissue tropism and the associated pathology of two autochthonous SRLV field strains of different tissue origin using an experimental infection in sheep via the bone marrow route and to determine if SRLV lesions could be produced in this experimental model.…”