Distribution of atypical porcine pestivirus in the cerebellum of newborn piglets following in utero inoculation

Authors: Falkenberg, Shollie; ARRUDA, PAULO - Iowa State University; MAGSTADT, DREW - Iowa State University; SCHWARTZ, KENT - Iowa State University; Palmer, Mitchell; Greenlee, Justin; Neill, John; Ridpath, Julia; GATTO, IGOR - Sao Paulo State University (UNESP); ARRUDA, BAILEY - Iowa State University

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 7/17/2018
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Recently, a growing number of putative pestivirus species have been discovered, one of these, is a genetically distinct pestivirus designated atypical porcine pestivirus (APPV). It has been demonstrated by experimental inoculation and in field outbreaks that APPV is associated with congenital tremors (CT) in neonatal pigs, but APPV associated CT resolves over time in surviving piglets. Detection of APPV by RT-qPCR in the cerebellum of experimentally inoculated piglets has been noted, but virus distribution in the cerebellum and microscopic observation of virus infected areas have not been described. The aim of this study was to conduct a retrospective analysis of cerebellum samples from experimentally inoculated piglets to evaluate viral distribution of APPV and the potential implications associated with localization of the virus. To accomplish this objective, an RNAscope' assay was used for detection of viral RNA in the cerebellum. Piglets (n=36) infected in utero at 45 or 62 days of gestation with APPV or PBS were euthanized at 2 days of age were evaluated for viral staining patterns. Boars (n=2) infected in utero at 62 days of gestation with APPV were maintained after resolution of CT and euthanized at approximately 11 months for viral staining. RNAscope' probes were designed specific for the Npro-Erns coding region of the APPV strain used for experimental inoculation. In piglets viral RNA had multifocal distribution within granular layers that extended into the adjacent molecular layer, but rarely within the white matter or Purkinje cells. The degree of labeling varied between animals, ranging from one to several small foci to larger locally extensive areas. In the boars, extensive staining of the molecular and granular layers were observed with minimal to no areas that lacked viral staining. Minimal to no viral RNA was noted in the white matter of either piglets or boars, but variable numbers of vacuoles were observed in sections with increased virus labeling. This data highlights the inconsistency in the distribution of the virus in the cerebellum of piglets inoculated in utero and the extensive staining observed in boars in which CT have resolved. The variability in viral distribution observed in the piglets could impact RT-qPCR Cq values depending on the sample area collected. Further, the multifocal distribution in the piglets could provide insight into the process by which APPV infection in the cerebellum transitions from abnormal signals that may relate to control of the virus to localized regions to complete dissemination of the virus and tolerance of the persisting virus. It is unknown if resolution of CT correlates to complete dissemination of the virus in the cerebellum. Clinical evidence implicates the presence of an underlying abnormality of cerebellar function in CT as CT is characterized as an intention (i.e., “cerebellar”) tremor. The absence of clinical signs attributable to CT in the boars despite the extensive viral distribution is of interest. Investigations elucidating the cascade of biochemical and cellular events occurring in the cerebellum in CT as well as the physiological effects of secondary remodeling/rewiring that may be occurring in piglets with CT that result in resolution of clinical disease despite persistent infection of cells in the cerebellum may allow for translational avenues in tremor disorders.