Acute interstitial nephritis in dogs is caused most often by Leptospira interrogans (see Leptospirosis in Dogs Leptospirosis in Dogs Dogs are the primary host of Leptospira serovars, and many other mammal species can also be infected. Clinical signs range from mild, subclinical infection to multi-organ failure and death.... read more ). Cats rarely develop leptospirosis, and clinical signs are less severe than in dogs. Other infectious causes of nephritis in dogs include Leishmania donovani and Borrelia burgdorferi. These systemic vectorborne diseases are endemic in specific geographic areas. Glomerulonephritis is the predominant renal pathology, so these are considered immune complex diseases rather than true urinary tract infections. Toxoplasmosis can cause pyogranulomas in the kidneys or elsewhere in the urinary system. Systemic infectious diseases that cause vasculitis in cats or dogs (eg, feline infectious peritonitis, Rocky Mountain spotted fever) may also cause kidney disease.