7-year-old male Fulvous whistling duck (Dendrocygna bicolor)
Marked caudal coelomic distension with a very firm mass was noted. Otherwise, the duck showed no clinical signs. A CBC revealed a heterophilic (13,710/ul) leukocytosis (21,240/ul), and on serum chemistry analysis there was marked hypoalbuminemia (0.2 g/dl) and mildly increased uric acid (10.4 mg/dl). Radiographs confirmed a large soft tissue density extending from the mid- to caudal coelomic cavity and displacing the intestines caudally. The duck was euthanized.
A 7-year-old male fulvous whistling duck was presented in fair nutritional condition with marked firm distension of the caudal coelomic cavity due to a massively and diffusely enlarged liver (21% of body weight).Â The capsular surface of the liver was rough, slightly irregular, and tan with several indistinct irregular white foci, predominantly on the right lobe (Fig.Â 3-1).Â On cut section, these foci corresponded to firm, coalescing 0.2 to 1 cm diameter nodules with thick white capsules around brown caseous centers which replaced approximately 95% of the parenchyma of the right lobe and were scattered in small numbers throughout the left lobe (Fig.Â 3-2).Â The remaining hepatic parenchyma was pale tan, firm and waxy.Â Additional very firm, multinodular, pink and tan mottled masses composed of encapsulated caseous material were present in the fascia of cervical area, dorsal to the syrinx, and attached to the serosa of several loops of intestine.Â The spleen and kidneys were also markedly enlarged.
In two sections of liver examined, the parenchyma is moderately to severely disrupted and replaced by abundant amorphous pale eosinophilic extracellular hyaline material (consistent with amyloid) and multifocal to coalescing granulomas (Fig.Â 3-3).Â Deposition of the hyaline material variably expands the space of Disse and vessel walls, separating and disrupting cords of shrunken (atrophic) hepatocytes and occluding sinusoids.Â In other areas, coalescing sheets of hyaline material replace large areas of the parenchyma, with only small islands of hepatocytes and hyperplastic bile ducts remaining(Figs.Â 3-4, 3-5).Â Hyaline material is also frequently present within Kupffer cells and the numerous multinucleated giant cells.Â The granulomas consist of a dense core of amorphous and cellular hypereosinophilic debris mixed with large numbers of wispy, amphophilic bacterial colonies surrounded by a thick rim of multinucleated giant cells and numerous fibroblasts, lymphocytes and plasma cells with fewer heterophils.
Liver: Severe multifocal to coalescing granulomatous hepatitis with intralesional acid-fast rod bacteria (Fig.Â 3-6) (Mycobacterium avium complex)
Liver: Severe amyloidosis
With Congo red staining, the suspected amyloid was diffusely dull brick red and had a variable apple green birefringence under polarized light.Â This staining was lost when tissues were pretreated with potassium permanganate (KMnO4).Â Electron microscopy confirmed that the deposits were extracellular and composed of long, haphazardly-arranged, non-branching fibrils that were on average 10 nm in diameter.
Both Ziehl-Neelsen and Fites stains showed very large numbers of thin, variable length, acid-fast rods admixed with the debris at the center of the granulomas and occasionally within the surrounding multinucleated giant cells.Â These bacteria were gram positive with a Brown & Brenn stain.Â Immunohistochemical staining for Bacillus Calmette-Guerin (BCG) showed abundant amorphous immunoreactive material within the granulomas.Â The organism was identified as Mycobacterium avium complex by HPLC at the National Jewish Medical Center.
Mycobacterium avium; amyloidosis
This duck had systemic amyloidosis secondary to a chronic disseminated mycobacterial infection.Â In both birds and mammals with this type of amyloidosis, the liver, spleen, and kidney are most consistently involved, with variable involvement of other organs.(1,5) In addition to the liver in this case, the spleen, kidneys (interstitium and glomeruli), and adrenal glands were severely affected, but amyloid was also present in the vessel walls/interstitium of the thyroid glands, parathyroid glands, testes, bone marrow, lungs, and heart.Â As was demonstrated in this case, the deposits begin in the space of Disse (liver), within vessel walls, and along basement membranes, eventually leading to disease through compression of adjacent tissue and/or restriction of blood flow.(1,5)
The term amyloid encompasses a group of biochemically distinct proteins with a similar beta-pleated sheet conformation arranged in variable length, 7.5-10 nm wide, nonbranching filaments (visible by electron microscopy) which give amyloid its characteristic Congo red staining and green birefringence, as well as its fluorescence with thioflavin-T or S.(1,4,5) At least 17 amyloid proteins have been characterized in humans and animals, with AA (derived from serum amyloid A), AL (derived from immunoglobulin light chains), and AÎ² (Î²-amyloid protein found in cerebral Alzheimer disease lesions) being the most common in humans.(1) Of these, except for a single report of Î²-amyloid in cerebral vessels of an aged woodpecker, (7) only AA-amyloidosis has been reported in birds.(5) The precursor protein for AA, serum amyloid A (SAA), is a soluble acute phase response protein synthesized in the liver in response to inflammation via cytokines Il-1, Il-6, and TNF.(1,4,5) The mechanisms by which insoluble derivatives of SAA are deposited and accumulate are poorly understood, but because of its association with persistently elevated SAA concentrations, as occurs in chronic inflammatory conditions, this type of amyloidosis is known as secondary, or reactive, amyloidosis.
Among birds, amyloidosis has been reported in most orders, but is particularly common in captive Anseriformes where incidences may be almost 80% in ducks and 50% in geese and swans examined at necropsy.(5) In approximately 60-70% of amyloidosis cases in Anseriformes, an associated chronic inflammatory or infectious disease, such as mycobacteriosis, fungal disease, or enteric parasites, can be identified.(2,5,10) It has also been associated with bumblefoot in Pekin ducks and can be induced experimentally in ducks and chickens with injections of a variety of bacterial and adjuvant components.(5) The cases in which systemic amyloidosis is present without inflammation may be considered idiopathic or a result of nonspecific stresses associated with environmental conditions.Â For example, a study in white Pekin ducks free of chronic disease and parasites showed that increased crowding corresponded to increased rate and incidence of development of amyloidosis.(3) Amyloidosis has been seen in approximately 20% of avian mycobacteriosis cases overall, (6) and in up to 50-60% of the cases in Anseriformes.(2,8)
Mycobacteriosis in birds is predominantly caused by Mycobacterium avium-intracellulare (MAI) complex organisms or Mycobacterium genavense and is spread by fecal-oral transmission (rarely aerogenous) from environmental contamination.(9) They have low zoonotic potential, except to immunocompromised individuals, who are nevertheless more likely to acquire the infection from a common environmental source.(9) Some studies have found disproportionate susceptibility of waterfowl, especially perching ducks, to Mycobacterium sp.Â in zoologic collections.(9) The infection in this duck was systemic with severe involvement of the liver and scattered granulomas present in the spleen, on the serosal surface of the intestinal tract, and in the fascia of the cervical and syringeal regions.Â It was identified as a Mycobacterium avium complex species.Â
1.Â Liver: Granulomas, multiple, with acid fast bacilli, etiology consistent with Mycobacterium sp.
2.Â Liver: Amyloidosis, diffuse, severe, with moderate hepatocellular atrophy, loss, degeneration, and necrosis and multifocal, moderate granulomatous hepatitis
The conference discussion centered predominately on the different types of amyloid and the cytokines involved in inflammation and amyloidosis.Â Scattered granulomatous inflammation in some areas did not appear to be associated with the acid-fast bacteria.Â The contributor did an outstanding job of describing this entity.Â
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