Amyloid A amyloidosis associated with Streptococcus suis infection in a young commercial pig with wild-type serum amyloid A.

Amyloid A (AA) amyloidosis is a progressive disease caused by the deposition of AA, an abnormally folded protein derived from serum amyloid A (SAA), in organs throughout the body. AA amyloidosis occurs in various mammals and birds but is extremely rare in commercial pigs. A possible reason for this is that a variant SAA is crucial for the onset of AA amyloidosis in pigs. However, AA amyloidosis with wild-type SAA was recently reported in microminipigs, which are the smallest laboratory pigs, leaving the importance of this variant unclear. This is a report of the involvement of wild-type SAA in AA amyloidosis in 4-month-old three-way crossed pigs (Landrace, Large White, and Duroc: LWD). Using immunohistochemistry, transmission electron microscopy, mass spectrometry, and DNA sequencing, we determined that the amyloid fibrils were derived from wild-type SAA without detectable variant, which is a rare finding in commercial pigs. This finding suggests that AA amyloidosis can occur in commercial pigs regardless of the presence of the SAA variant.