Amyloidosis in Domestic Animals: Pathology, Pathogenesis, Gross and Microscopic Lesions and Clinical Findings

Amyloidosis refers to a group of protein misfolding diseases characterized by deposition of a particular amyloid protein in various organs and tissues of animals and humans. Although there are other components present in the deposit, the amyloid protein fibril is the main component of the amyloid substance. The amyloid substance differs in protein composition depending upon the types of amyloidosis (AA amyloidosis or AL amyloidosis) and the different clinical forms. Each clinical entity or form of amyloidosis may be manifested by a distinct clinical form with chemically specific amyloid fibril protein. This indicates that amyloid is a biochemically heterogeneous substance, although there are similarities in properties and staining characteristics. Amyloidosis involving several tissues and organs throughout the body is referred to as systemic amyloidosis. This may be AA amyloidosis (including familial amyloidosis) or AL amyloidosis. Systemic amyloidosis can be deposited in several vital organs and tissues and may entail severe damage. Amyloid substance may be confined at a given area in the body in the form of localized amyloidosis. The pathogenesis, pathology and clinical presentations of amyloidosis are protean consequent to the diverse underlying causes of its various forms, species of animals affected and the severity of functional disruption in different tissues and organs involved. The diagnosis of amyloidosis requires histopathologic identification of amyloid deposits in the affected tissues. This is confirmed by Congo red staining and green birefringence under polarized light. In this chapter, the pathology, pathogenesis, lesions, and clinical syndromes encompassing various forms of amyloidosis in animals will be covered. Current knowledge available on amyloidosis in animals, which would be of importance as a reference for veterinary professionals and practitioners, and veterinary students will be elucidated in the chapter.