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Development of Microalbuminuria in Dogs with Heartworm Disease

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SUMMARY:

• Heartworm infection is a well established model of kidney disease. Circulating antigen-antibody complexes damage glomeruli.
• Dogs became positive for microalbuminuria within 2-3 months of becoming positive for circulating heartworm antigen.
• Presence of microalbuminuria correlated with presence of histologic lesions in glomeruli of heartworm infected dogs.
• Study demonstrates microalbuminuria as sensitive indicator of glomerular damage.

The presence of microalbuminuria (MA) has been shown to be an accurate predictor of subsequent renal disease in human beings with both systemic hypertension and diabetes mellitus. MA has also been observed in human beings with systemic diseases that are associated with glomerulopathy. Previous studies in dogs have shown the prevalence of MA in apparently healthy dogs and soft coated wheaten terriers genetically predisposed to developing glomerular disease to be 19% and 76%, respectively. The purpose of this study was to determine the prevalence of MA in dogs with experimentally infected heartworm disease. Twelve six-month male beagles were randomly divided into two groups of six. Group A was fed a diet with a 50:1 n-6: n-3 fatty acid ratio and group B was fed a diet with a 5:1 n-6: n-3 fatty acid ratio. All of the dogs were infected subcutaneously with 75 Dirofilaria immitis infective larvae. Urine collections via urethral catheterization were performed monthly for 14 to 23 months post infection. Urine albumin concentrations were measured using an antigen capture ELISA. To account for varying urine concentrations, results were normalized to a specific gravity of 1.010. MA was defined as urinary excretion of albumin greater than 1.0 mg/dl but less than 30.0 mg/dl.

All dogs developed MA; the initial month of detection of MA was different between groups as measured by ANOVA (Group A 7.5±1.9 vs Group B 9.7±1.0, P=0.032). After the initial episode of MA, 67/82 (82%) of samples from Group A dogs had MA and 4/82 (5%) samples had overt proteinuria (>30 mg/dl). The average concentration of urine protein in these 82 samples was 7.7±11 mg/dl. In comparison, after the initial episode of MA, Group B dogs had 45/68 (66%) samples with MA and 7/68 (10%) samples with overt proteinuria. The average concentration of urine protein in these 68 samples was 8.3±14 mg/dl. In both groups MA increased over time and MA preceded overt proteinuria when it occurred. The overall number of proteinuric urine samples (>1.0 mg/dl) in both groups after the initial onset was 123/150 (82%) with 75% of the samples having MA and 7% having overt proteinuria. Eleven of these 12 dogs had histologic evidence of glomerular lesions on light microscopic and/or immunocytochemical evaluation.

This study shows that the prevalence of MA in dogs with experimentally infected heartworm disease is higher than that observed in apparently healthy dogs and similar to that observed in soft coated wheaten terriers. Further study is necessary to determine if all heartworm-infected dogs with MA will progress to develop overt proteinuria.

Reproduced with permission of the Journal of Veterinary Internal Medicine.