acute interstitial nephritis is the cause of acute renal failure in about 1520% of cases . many factors lead to interstitial nephritis , which can be categorized into different forms : drug related hypersensitivity reaction , infection , immune - mediated diseases , hereditary , metabolic and idiopathic . within these broad categories , nowadays drugs are the predominant cause of interstitial nephritis , followed by infections and idiopathic lesions . acute pyelonephritis caused by renal invasion of virulent microorganisms has to be distinguished from acute interstitial nephritis , which can occasionally be seen in the setting of systemic bacterial and viral infection as a hypersensitivity reaction , whereas it is uncommon in human parasitic infections . giardiasis is an infection of the small intestine caused by giardia lamblia ( also known as g. intestinalis ) , a flagellate protozoan . giardiasis is the most commonly reported pathogenic protozoan disease in the usa and in europe . travelers are the largest risk group for giardiasis infection , especially those who travel to the developing world . giardiasis is spread via the fecal - oral route and its prevalence rates range from 27% in developed countries and 2030% in most developing countries . the center for disease control estimates there are up to 2.5 million cases of giardiasis annually . the most common symptoms of giardia infection include diarrhea for a duration of more than ten days , abdominal pain , flatulence , bloating , vomiting , and weight loss , but approximately 50% of infections are characterized as asymptomatic . giardiasis is diagnosed by the detection of cysts or trophozoites in the feces , trophozoites in the small intestine , or by the detection of giardia antigens in the feces . we report the case of a woman who developed an impairment of renal function , after a prolonged period of slight fever and diarrhea . a 54-year - old female had fever ( maximum 38c ) and diarrhea for approximately ten days . because of an elevated serum creatinine ( 3.0 mg / dl ) , she was admitted to our unit . laboratory investigation revealed elevated c - reactive protein of 80 mg / dl ( normal range 010 mg / dl ) and elevated erythrocyte sedimentation rate of 120 mm / s . complete blood cell count revealed leukocytosis of 11,40010/ml ( normal range 410 ) with eosinophilia of 0.4510/ml ( 3.9% of white blood cells ) . testing for autoimmune antibodies , such as antinuclear antibodies , antiphospholipid antibodies , antineutrophil cytoplasmatic antibodies , antiglomerular basement membrane antibodies , as well as hepatitis b surface antigen and light chain proteinuria were negative . blood , urine , sputum and stool culture were negative . because of the prolonged period of diarrhea , a screening for parasitic infections was performed and giardia lamblia was found . therefore , a therapy with metronidazole ( 500 mg / tid per 7 days ) was administered . after an attempt to recover renal impairment by vigorous rehydratation , because of the unclear origin of the persisting renal failure , a percutaneous renal biopsy was performed . histological examination showed cortically accentuated interstitial nephritis with a dense peritubular infiltrate of lymphocytes , monocytes and granulocytes ( figure 1 ) . after successful treatment of the underlying giardia infection , clinical symptoms persisted and renal insufficiency had progressed further ( serum creatinine 5.7 mg / dl , creatinine clearance 8 ml / min ) . methylprednisolone 250 mg / die per three days was administered and followed by prednisone per os ( 0.5 mg / kg / die ) , maintained for two weeks . within three days , renal function started to improve and after six weeks , renal function had completely recovered . figure 1a ) glomerulus with regular basement membranes , typical mesangium and normal cell number . renal involvement in parasitic infections is polymorphic , ranging from direct invasion to various types of glomerulonephritis . acute interstitial nephritis as a form of hypersensitivity reaction is an uncommon manifestation in the setting of human parasitic infections . we present a case of acute interstitial nephritis in association with giardia infection of a 54-year old patient . a combination of antibiotic and steroid therapy led to eradication of the helminths and to full recovery of renal function . to date only a few cases of acute interstitial nephritis in parasitic infections ( i.e. ascaris lumbricoides infection ) have been described in the literature and this is , in our knowledge , the first case of giardiasis reported . giardia intestinalis affects about 30% of the world population , but acute interstitial nephritis is rarely seen and seems to be a quite uncommon complication in the course of infection , even when we consider that most infections occur in developing countries . in fact , in these countries medical standards are low and intermittent impairment of renal function might be underdiagnosed , as patients only have limited access to medical care . it is known that host genetics is an important determinant of the intensity and time course of most parasitic infections . a special genetic or allergic predisposition could , therefore , have been the reason for the renal involvement in this patient . it is also possible that giardia - derived antigens themselves did not lead to acute interstitial nephritis but had a permissive effect on other inflammatory stimuli in susceptible patients . in conclusion , in cases of unexplained renal failure in patients affected by parasitic infections , interstitial nephritis should be considered and a renal biopsy should be performed .
acute interstitial nephritis is a relevant cause of acute renal failure . 
 drugs are the predominant cause , followed by infections and idiopathic lesions . 
 acute interstitial nephritis as a form of hypersensitivity reaction is an uncommon manifestation in the setting of human parasitic infections . 
 we present a case of acute interstitial nephritis in association with giardia infection in a 54-year - old woman who developed an impairment of renal function after a prolonged period of slight fever and diarrhea . after an attempt to recover renal impairment by vigorous rehydratation , 
 because of the unclear origin of the persisting renal failure , a percutaneous renal biopsy was performed and a diagnosis of severe acute interstitial nephritis was made . 
 steroid therapy was started and after six weeks , renal function had completely recovered . in cases of unexplained renal failure in patients affected by parasitic infections , 
 interstitial nephritis should be considered and it is our opinion that a renal biopsy should be always performed .