Abstract

Atherosclerosis and nephrosclerosis have been described in captive and wild howlers.^5,7 This report describes the occurrence of glomerular atherosclerosis and nephrosclerosis in five black howlers (Alouatta caraya), three red howlers (Alouatta seniculus sara) and one golden howler (Alouatta seniculus straminea) from two zoological facilities in the United States. Table 1 summarizes the signalment and history for each animal. Two were males and seven were females. Age at necropsy ranged from 5–26 years, and average age was 16.1 years. Five animals died and four were humanely euthanatized. The most common reported historic findings included chronic renal failure (three animals), protein-losing nephropathy (two animals), weight loss (three animals), depression or lethargy (three animals) and constipation (two animals). Serum chemistries were available for seven monkeys and abnormal values included azotemia (seven animals), elevated serum creatinine (seven animals), hypoalbuminemia(seven animals), hypoproteinemia (six animals), hypercholesterolemia (five animals), and hyperphosphatemia (five animals). Urinalyses were available for four monkeys and abnormal values included proteinuria (three animals), hematuria (three animals), and glucosuria (three animals).

Table 1. Signalment and history for howler monkeys with glomerular disease

^aM=male; F=female.
^bAnimal was on fluid therapy at time urinalysis was obtained.
^cNot available.
^dMost recent bloodwork was 5 months prior to death.

Table 2 summarizes the gross and histologic findings for each animal. The most common gross findings were small, shrunken or scarred kidneys (seven animals), globoid or hypertrophic heart (four animals), thoracic or pleural effusions (four animals), aortic or valvular plaques (two animals), endocardiosis (two animals) and yellow fat (two animals). Histologically, all animals had varying and generally severe glomerular and renal vascular atherosclerosis, membranoproliferative and mesangioproliferative glomerulopathy, renal tubular protein casts, nephrosclerosis, and chronic interstitial nephritis. Extra-renal arteriosclerosis and atherosclerosis were detected in seven animals, especially in the heart and aorta. Eight animals had varying degrees of myocardial fibrosis. Some additional histologic findings included chronic enteritis or enterocolitis (six animals), pancreatic acinar cell atrophy (four animals), hemosiderosis in lymph nodes gut or liver (three animals), atrophy of fat (three animals), islet cell hyperplasia (two animals), and hyperplastic goiter (two animals).

Table 2. Gross and histologic lesions associated with glomerular disease in howler monkeys

^aMembranoproliferative glomerulonephritis.
^bChronic interstitial nephritis.

The renal lesions in these howlers were attributed to atherosclerosis, hypertension, ischemia, and aging. Glomerular protein leakage and tubular protein casts were attributed to glomerular atherosclerosis and glomerulosclerosis. The nephrosclerosis and chronic interstitial nephritis were attributed to tubular abrogation associated with protein casts as well as ischemic change associated with hypertension and atherosclerosis. The presentations in these animals are similar to various nephropathies described in humans that are associated with acquired derangements in lipid metabolism, atherosclerosis, diabetes mellitus, and hypertension.^2-4,8-10 High circulating levels of low-density lipoproteins, glomerular-free radical injury, and ischemia are believed to play important roles in the development of chronic renal disease in humans.^2-4,8-10 Chronic renal disease with protein losing nephropathy and atherosclerosis appear to be over-represented in captive howler monkeys fed diets that may not be considered atherogenic in other species, indicating that these animals may be exquisitely sensitive to the affects of hypercholesterolemia, atherosclerosis, and associated development of renal disease.^1,5-7,11 Strict dietary management and periodic monitoring of serum cholesterol levels may be indicated for howler monkeys.

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