Heartworm Effects on the Kidney

Persistent proteinuria is predictive of worsening prognosis in cats and dogs with chronic renal failure. Dogs infected with heartworms may develop proteinuria from renal lesions. This study evaluated proteinuria in cats infected with heartworm disease. Group 1 cats (n = 80) were experimentally infected as part of a drug safety study. Group 2 cats (n = 31) were naturally infected cats that were studied retrospectively. Each group included a control population. Cats in group 1 were inoculated with 60 Dirofilaria immitis larvae. Heartworm serum antigen and antibody testing and modified Knott’s tests were conducted approximately 8 months after infection. Urine samples from 64 of 80 cats were collected at 8 months and/or 12 months after infection. Ten of these cats were microalbuminuric at 8 months after infection. None of the control cats or cats refractory to infection with larvae had protein in its urine. There was a subtle but significant association between worm burden and proteinuria. In group 2 cats, proteinuria was quantified retrospectively from urine dipstick results. These cats had a significantly greater incidence of proteinuria (90% vs 35%) as compared with age- and gendermatched controls. Although the clinical relevance of proteinuria has yet to be determined, cats infected with mature adult heartworms are at risk for proteinuria. Study supported by Bayer Animal HealthCare LLC, HESKA Corporation, and IDEXX Laboratories

Commentary: Another concern about heartworm infection in cats is suggested by this study. Clinical signs of heartworm infection can be nonspecific and mimic other diseases. Cats infected with heartworm may vomit, be lethargic, lose weight, cough, or have asthma-like clinical signs (labored, rapid breathing). Diagnosis from clinical signs alone is almost impossible, so many cases may be missed. Although the clinical relevance of heartworm-associated proteinuria is unknown, the long-term effects on the kidney should be further evaluated.—Patricia Thomblison, DVM, MS

Renal effects of Dirofilaria immitis in experimentally and naturally infected cats. Atkins CE, Vaden SL, Arther RG, et al. VET PARASITOL doi: 10.1016/j.vetpar.2011.01.016.