Abstract

A captive, 8-yr-old, intact, male pygmy marmoset (Callithrix pygmaea) was evaluated during an annual exam. While no prior health issues had been appreciated, the animal was thin and blood tests demonstrated azotemia. Subsequent testing showed azotemia with isosthenuria and proteinuria, leading to a diagnosis of renal disease, tentatively involving the glomerulus and tubules. Diagnosis of renal disease in callitrichids is possible utilizing standard techniques; however, patient size makes it difficult to run all urine tests at one time. Routine behavioral training protocols were essential in managing this case. A target station provided a physical platform for regular urine collection and training sessions allowed routine weight evaluation and individualized medication administration. Routine monitoring for proteinuria may be utilized as a screening tool for renal disease.

Introduction

The presence of azotemia in association with isosthenuria is highly suggestive of renal insufficiency.⁵ Tubular and glomerular disease may exist concurrently, and glomerular disease will frequently progress to severe tubular damage.⁵ Significant functional loss occurs prior to elevations in blood chemistry values.⁵ In glomerular disease such as glomerulonephritis, the urine protein:creatine ratio (UPC) may be utilized to detect problems before azotemia develops.⁵ Urine protein:creatine ratio values greater than 1.0 are indicative of renal disease, including some tubular disease, with higher values being associated with glomerular disease. Urine protein:creatine ratio needs to be evaluated in combination with urine sediment as significant levels of red or white blood cells will increase the ratio. In addition, cases should be evaluated for extrarenal sources of protein.^4,5 Definitive antemortem diagnosis of renal disease requires kidney biopsy.⁵

A syndrome linking glomerulonephritis, presumed hypertension, heart failure and death has been described in callitrichids.⁸ While postmortem diagnosis of immune complex deposition and renal failure in callitrichid species exists in the literature, antemortem description of renal disease is lacking.^1,2,8,11 Early diagnosis of renal disease can improve management options for animals and lead to better understanding of disease progression.^4-7,9,10

Case Report

An 8-yr-old, male pygmy marmoset was evaluated during a routine exam. The animal was housed with one other adult male pygmy marmoset in the Amazon Exhibit of the John G. Shedd Aquarium. Keeper staff did not identify health concerns prior to sedation but body condition appeared thin on physical exam. Isoflurane (lso-thesia, Abbot Laboratories, North Chicago, IL, USA, 1–5%) in oxygen administered in a chamber, then via facemask, was utilized for anesthesia. Serum chemistry analysis showed azotemia (Table 1). Whole body radiographs were considered normal. A voided urine sample collected 3 days later was isosthenuric, with proteinuria and negative sediment (Table 2). A second voided sample collected on day 6 showed isosthenuria and proteinuria. A tentative diagnosis of renal disease, possibly glomerulonephritis, was made based on azotemia, isosthenuria, and proteinuria with inactive sediment. A urine protein:creatine ratio run on day 12 was 13.6.

On day 15, the animal was re-sedated in an attempt to collect blood and urine for evaluation on the same day. Bloodwork showed anemia, azotemia, and hypoalbuminemia. Voided urine collected on the same day was isosthenuric with inactive sediment but no protein was present. A drop of urine expressed from the bladder was cultured and yielded scant growth of three organisms, considered to be contaminants. Ultrasound showed small, hyperechoic kidneys. Measurements were not taken due to concerns over patient stability.

Table 1. Selected CBC and serum chemistry values for a pygmy marmoset (Callithrix pygmaea)

^aHematocrit.
^bBlood urea nitrogen.
^cInternational Species Information System, Apple Valley, Minnesota, 55124 USA; Callithrix pygmaea; physiologic reference ranges for males >2 yr old, March 2002.

Table 2. Selected urine values for a pygmy marmoset (Callithrix pygmaea)

^aUrine specific gravity.
^bNegative.
^cWhite blood cells/high power field.
^dRed blood cells/high power field.

Enalapril maleate suspension (Martin Avenue Pharmacy, Naperville, IL, USA, 0.5 mg/kg PO every 12 h) was used to treat for renal failure related to possible glomerulonephritis as it has been associated with increased longevity in some cases.^3,5 Derm® Caps ES (DVM Pharmaceuticals, Inc., Miami, FL, USA, 1 drop PO every 25 h) was used to supply omega 3 fatty acids, which may be renoprotective.³ Supplemental feeding with Ensure® liquid (Abbott Laboratories, North Chicago, IL, USA) was begun to increase caloric and fluid intake.

Subsequent monitoring included sedation with sevoflurane in oxygen via chamber and facemask (SevoFlo, Abbott Laboratories, North Chicago, IL, USA, 3–7%) on day 43 for a repeat examination. Bloodwork demonstrated progressive azotemia and continued anemia. Blood pressure was measured noninvasively using a modified digit cuff (Pedisphyg, CAS Medical Systems, Inc., Branford, CT, USA). A systolic value of 100 mm Hg was obtained. Ultrasound of the heart demonstrated adequate contractility although measurements were not obtained due to concerns over patient stability. Three subsequent urine samples were collected opportunistically for UPC (4.7–18.7) and two fecals were negative for occult blood.

Seventy-two days after initial evaluation, cimetidine hydrochloride (Cimetidine Hydrochloride Injection 150 mg/ml, Endo Pharmaceuticals Inc., Chadds Ford, PA, USA, 4 mg/kg PO every 8 h) and metoclopramide (Metoclopramide Injection 5 mg/ml, Endo Pharmaceuticals, Inc., Chadds Ford, PA, USA, 0.1 mg/kg PO every 6 h) were started to alleviate possible nausea. The animal died 97 days after initial exam.

Necropsy and histopathology were completed. Histopathology showed diffuse, severe interstitial fibrosis and tubular loss with marked tubular and glomerular ectasia ("end stage" renal disease).¹⁰ Mild, multifocal lymphoplasmacytic interstitial nephritis was also noted. Moderate, multifocal arteriosclerosis was present in the renal blood vessels and left ventricular hypertrophy with mild, multifocal interstitial fibrosis was evident grossly. The cardiac changes were attributed to possible hypertension secondary to renal disease.

Discussion

Ideally, blood and urine tests are run from samples collected at the same time. Urinalysis with sediment exam, culture, and UPC are run on the same clean, free-catch, catheterized, or cystocentesis sample. Due to small sample size in this patient, however, it was difficult to monitor all urine parameters at one time. Attempts to overcome this were made by running tests multiple times and running different tests in a short time period. Overall, six of seven urine tests for protein (UPC and dipstick combined) demonstrated significant protein elevation. A simple method for collecting samples from an awake animal was developed. Urine samples were collected opportunistically from a plastic platform hung in the cage during daily training sessions. Samples could be obtained reliably and did not involve altering feeding or drinking schedules. Platforms were cleaned, then washed with copious amounts of water after each session. Urine samples obtained in this manner from a healthy conspecific had UPCs consistently <1.0.

The animal in this report had severe interstitial disease and glomerular ectasia. Glomerular disease, such as glomerulonephritis, in other species is associated with UPCs well over 1.0,^4,5 as seen in this case. The lack of obvious glomerular membrane change is interesting in this individual. One possible explanation is the presence of minimal change glomerulonephritis in which glomerular damage without obvious membrane change is present.³ Electron microscopy and immunohistochemical staining of kidney samples are needed to evaluate the full extent of glomerular lesions. Extraglomerular sources of urine protein and contamination^3,4 were not believed to be contributing to urine protein value measurements but cannot be completely ruled out. Urine obtained in the same manner from a normal conspecific consistently had UPC <1.0.

The renal vascular and cardiac changes seen at necropsy and on histopathology were supportive of possible hypertension.⁸ Hypertension is commonly seen with renal disease but is defined in antemortem testing.¹⁰ There is value to measuring and recording blood pressure in individual animals using a standard site-specific protocol. Evaluating pressure trends over time contributes to better monitoring of disease development as well as response to treatment. In this case, we only obtained one value, so were unable to evaluate a trend.

Renal biopsy is needed to definitively diagnose renal disease antemortem; however, obtaining a renal biopsy in small patients can be associated with severe hemorrhage and ischemic injury to the kidney and would be challenging in this species.⁴ Investigation of microsurgical or laparoscopy techniques may be warranted for this procedure.

Behavioral training was essential in case management. Weights could be obtained frequently and daily training sessions facilitated urine collection and medication administration.

Conclusion

Given the reported prevalence of renal disease in this species, regular monitoring for proteinuria is warranted. Urine can be collected reliably from awake animals with training. At the John G. Shedd Aquarium, UPC evaluation is currently performed monthly. Consistent elevations in protein warrant closer evaluation for renal disease. Early diagnosis may be helpful in improving quality of life, prolonging life, and better defining disease syndromes in this species.^4,5

Acknowledgments

Special thanks to Allan Pessier, DVM, Dipl ACVP, of the University of Illinois Zoo Pathology Program for his support in consultations on this case and for performing the necropsy and histopathology. The animal care staff of the aquarium and marine mammal collections at the John G. Shedd Aquarium was diligent in their care of this animal and have consistently advanced the level of behavioral training with this species.

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