Characterization of Pestivirus scrofae infection in the tissues of a persistently infected boar

Pestivirus scrofae (previously atypical porcine pestivirus, APPV) is a member of the genus Pestivirus within the family Flaviviridae. This virus has been established as the etiological agent of congenital tremor (CT) type AII, a neurological disorder in newborn piglets characterized by generalized tremors. Despite this association, the epidemiological characteristics of the virus, including its transmission dynamics and patterns of spread between herds, remain poorly understood. It has already been confirmed that, similarly to other flaviviruses, APPV can be shed by semen. Previously, we have identified interstitial Leydig cells, the peritubular myoid cells and smooth muscle cells of medium-sized arteries as target cells of APPV in the testicles of newborn, congenitally infected, CT-affected piglets.

In our present study, we examined FFPE tissue samples obtained from a persistently infected 6-months-old, sexually mature boar, born with CT, that was still shedding 2.1 × 10⁹ GE/mL APPV in its semen. We detected viral genome by RNAscope in situ hybridization method in the T-cell zones of the lymph nodes draining the reproductive organs and the GALT of the ileum, periarteriolar lymphoid sheaths of the spleen and in cells of the intestinal crypts in the ileum. We also identified positive cells in the molecular, granular and the Purkinje-cell layer of the cerebellum, and in the neurons of the spinal cord and the cerebral cortex. We found weak positive signal in the colon, but none in the lungs and the liver. Interestingly, positive signals were detected in the outer layers of the adrenal gland cortex (zona glomerulosa and fasciculata), as well as in the acinar cells of the exocrine pancreas. In reproductive organs, viral nucleic acid was detected in the Leydig cells and peritubular myoid cells of the testicles, in cells within the seminiferous tubules and in the epididymis. We also found positive cells in the prostate and the bulbourethral gland. The shedding of the virus in semen supports the notion that infected cells within the reproductive tract may serve as a source of the virus in semen. These affected cells of the reproductive tract could serve as source of the virus in semen.

Our results suggest that APPV is capable of crossing the blood-testis barrier, and may be associated with persistent infection, including cases likely originating from congenital exposure, in pigs and boars that can actively shed the virus. Therefore, the use of such animals for breeding purposes should be approached with caution. Further research is needed to elucidate the underlying mechanisms of persistent infection.