Identification of porcine reproductive and respiratory syndrome virus in semen and tissues from vasectomized and nonvasectomized boars

Previous studies have indicated that porcine reproductive and respiratory s yndrome virus (PRRSV) can be identified in and transmitted through boar sem en. However, the site(s) of replication indicating the origin of PRRSV in s emen has not been identified. To determine how PRRSV enters boar semen, fiv e vasectomized and two nonvasectomized PRRSV-seronegative bears were intran asally inoculated with PRRSV isolate VR-2332. Semen was collected three tim es weekly from each boar and separated into cellular and cell-free (seminal plasma) fractions. Both fractions were evaluated by reverse transcriptase nested polymerase chain reaction (RT-nPCR) for the presence of PRRSV RNA. V iremia and serostatus were evaluated once weekly, and boars were euthanatiz ed 21 days postinoculation (DPI). Tissues were collected and evaluated by R T-nPCR, virus isolation (VI), and immunohistochemistry to identify PRRSV RN A, infectious virus, or viral antigen, respectively. PRRSV RNA was identifi ed in semen from all vasectomized and nonvasectomized boars and was most co nsistently found in the cell fraction, within cells identified with a macro phage marker. Viral replication as determined by VI was predominately found within lymphoid tissue. However, PRRSV RNA was widely disseminated through out many tissues, including the reproductive tract at 21 DPI. These results indicate that PRRSV can enter semen independent of testicular or epididyma l tissues, and the source of PRRSV in semen is virus-infected monocytes/mac rophages or non-cell-associated virus in serum. PRRSV-infected mocrophages in semen may result from infection of local tissue macrophages or may origi nate from PRRSV-infected circulating monocytes or macrophages.