Ovine pulmonary carcinoma (OPC) is a contagious pulmonary neoplasia with a suspected retroviral etiology. The major core protein (P27) of the putative OPC virus cross-reacts with antibodies to P27 of the Mason-Pfizer monkey virus (MPMV), a type-D retrovirus. This serological reactivity serves as the only accepted biological marker for OPC. In order to make a useful reagent for the detection of the OPC marker for serodiagnosis and epidemiological studies, the MPMV-P27 coding region was cloned and expressed in Escherichia coli. Gel purified recombinant MPMV-P27 protein was used to develop an immunoassay. This recombinant enzyme-linked immunosorbent assay (ELISA) was then used to screen 223 sera from US sheep and 176 sera from Italian sheep. In this study, we found: (1) a high prevalence of infection with the putative OPC retrovirus in sheep with chronic pneumonia; (2) a subclinical infection with OPC virus may be more common in US sheep than indicated by the rare recorded occurrence of pulmonary carcinoma; (3) an apparent association between ovine lentivirus (OLV) and OPC infection.
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