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ARS Home » Midwest Area » Ames, Iowa » National Animal Disease Center » Virus and Prion Research » Research » Publications at this Location » Publication #326166
Title: Prion infectivity detected in swine challenged with chronic wasting disease via the intracerebral or oral route

Author
item MOORE, S - Orise Fellow
item Kunkle, Robert
item SMITH, JODI - Iowa State University
item WEST-GREENLEE, M - Iowa State University
item Greenlee, Justin

Submitted to: Prion
Publication Type: Abstract Only
Publication Acceptance Date: 4/4/2016
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Chronic wasting disease (CWD) is a naturally-occurring, fatal neurodegenerative disease of North American cervids. The potential for swine to serve as a host for the agent of chronic wasting disease is unknown. In the US, feeding of ruminant by-products to ruminants is prohibited, but feeding of ruminant materials to swine, mink, and poultry still occurs. In addition, scavenging of CWD-affected cervid carcasses by feral pigs presents a potential risk for CWD exposure. The purpose of this study was to investigate the susceptibility of swine to the CWD agent following oral or intracranial experimental challenge. At 8 weeks of age, crossbred pigs were challenged by the intracranial route (n=20), oral route (n=19), or were left unchallenged (n=9). At approximately 6 months of age, the time at which commercial pigs reach market weight, half of the pigs in each group were culled (<6 month challenge groups). The remaining pigs (>6 month challenge groups) were allowed to incubate for up to 73 months post challenge (mpc). At death a complete necropsy examination was performed, including testing of tissues for misfolded prion protein (PrPcwd) by western blotting (WB), enzyme-linked immunosorbent assay (ELISA), and immunohistochemistry (IHC). None of the pigs developed clinical signs consistent with prion disease. Four >6 month intracranially challenged pigs (survival times 45-73 mpc) were positive by ELISA, two were also positive by WB, and one was positive by IHC. One >6 month orally challenged pig (64 mpc) was positive by ELISA. To further investigate the potential for infectivity, brain tissue from selected pigs was bioassayed in mice expressing porcine PRNP. Tissue from the two WB-positive >6 month intracranially challenged pigs produced positive bioassay results, albeit with low attack rates and variable incubation periods. Interestingly, bioassay of material from the longest surviving >6 month orally challenged pig (72 mpc), which was negative for PrPcwd by all other tests, produced a positive bioassay result. Bioassay of material from additional animals is currently underway. This study demonstrates that pigs can serve as potential hosts for CWD, although with low attack rates and scant PrPcwd accumulation. Detection of infectivity in orally challenged pigs using mouse bioassay raises the possibility that naturally exposed pigs act as a reservoir of CWD infectivity, even though affected pigs do not develop overt clinical signs or readily detectable PrPcwd.