Human polyoma virus (HPV)--a significant pathogen in renal transplantation.

Routine cytological screening of Papanicolaou-stained smears of the urinary sediment from 57 renal allografts in 51 patients has resulted in the detection of seven cases of Human Polyoma Virus (HPV) BK infection--14% of the total number. Infection was confirmed by virus isolation and electron microscopy (EM). The cytological, histological and ultra-structural data are described and related to the clinical progress of the patient. Four out of the seven cases are discussed in more detail as histological material was available; in three of these, there was evidence of stenosis of the transplant ureter with virus infected cells in the ureteric epithelium and in one case also in the renal tubules. Administration of high dose steroids may provoke active infection with HPV in ureteric epithelium damaged by ischaemia and inflammation. The similarity between the clinical features of an HPV infection and a rejection episode make it imperative to confirm the diagnosis quickly and accurately. Cytological examination of the urinary deposit by light microscopy is a simple, inexpensive procedure which provides positive diagnosis of the typical virus inclusions within an hour of receiving the urine specimen in the laboratory. This can be confirmed by removing single cells from the original cytological slide preparation and processing them for EM using a technique described by Coleman et al [1].