ABSTRACT
A study was undertaken to investigate the occurrence of ovine lentivirus (OvLV) infection in sheep with chronic respiratory disease on the Laikipia Plateau, Kenya. All seven Merino crossbred sheep with chronic dyspnoea and emaciation examined for gross and microscopic lesions had lymphoid interstitial pneumonia (LIP), and one also had pulmonary abscesses. Two of the sheep with LIP also had lesions of ovine pulmonary carcinoma (OPC, jaagsiekte). Using in situ hybridization, OvLV DNA localized to a high proportion of pulmonary macrophages in lungs with lesions of LIP. Lung tissue samples from six of these sheep were positive for a syncytium-inducing virus in cultures of lamb testis cells. Thin-section electron microscopy of infected cells showed virions with morphogenesis typical of lentiviruses. In a western blotting assay, monoclonal antibodies to the OvLV capsid (CA, p27) and matrix (MA, p15) proteins of a North American OvLV isolate reacted with similar-sized bands of the virus, and serum from six of the sheep were reactive with CA from the Kenyan viral isolate. Using an OvLV agar gel immunodiffusion (AGID) test, all seven sheep were positive for serum antiviral antibody, as were 29% of 63 clinically normal sheep from Laikipia District. However, when sera from the healthy sheep were tested in a western blot assay, only 52% had IgG reactive to the OvLV CA, indicating a high rate of false negative reactions with the AGID test. Serum samples from 87 Red Maasai or Dorper crossbred sheep from two farms in other parts of Kenya were OvLV seronegative by both the AGID test and the western blot assay. These results document the first identification of OvLV as a cause of chronic respiratory disease in sheep in Kenya and show a high rate of infection in sheep flocks, with a high prevalence of chronic respiratory disease.
Subject(s)
Lentivirus Infections/veterinary , Lentiviruses, Ovine-Caprine/isolation & purification , Lung Diseases/veterinary , Sheep Diseases/virology , Animals , Antibodies, Viral/blood , Blotting, Western , DNA, Viral/chemistry , DNA, Viral/isolation & purification , Histocytochemistry/veterinary , Immunodiffusion/veterinary , Lentivirus Infections/pathology , Lentivirus Infections/virology , Lentiviruses, Ovine-Caprine/ultrastructure , Lung Diseases/pathology , Lung Diseases/virology , Microscopy, Electron/veterinary , Nucleic Acid Hybridization , Polymerase Chain Reaction/veterinary , Sheep , Sheep Diseases/pathologyABSTRACT
Blood-brain barrier dysfunction has been postulated to be important in the pathogenesis of HIV dementia. This study used an in vitro model of the blood-brain barrier to determine the effects of ovine lentivirus (OvLV) infection on endothelial cells. The replication of two American OvLV isolates and two lcelandic OvLV isolates in pure cultures of endothelial cells isolated from brain was compared to replication in endothelial cells from adipose, lung, and aorta. Inoculation with the two American isolates resulted in 100 times greater reverse transcriptase (RT) activity in supernatant of the microvascular endothelial cells (brain, lung, and adipose) than in the macrovascular endothelial cells (aorta). Conversely, inoculation with the two lcelandic isolates resulted in 100 times higher RT activity in aortic, lung, and adipose endothelial cells than in the brain endothelial cells. Transmission electron microscopy of the brain capillary endothelial cells infected with the American isolates revealed polarized viral budding from the lateral cell membrane and a loss of tight junctions. Replication of OvLV in brain capillary endothelial cells could play a role in the pathogenesis of lentiviral encephalitis by altering blood-brain barrier integrity.
