Ultrastructure of renal lesions in pigs with acute leptospirosis caused by Leptospira pomona.

Twelve 4-day old, pathogen-free pigs were inoculated intraperitoneally with virulent L. pomona. Two pigs each were killed 1, 2, 3, 5, 7, and 14 days after inoculation and their kidneys examined by light and electron microscopy. Three to 5 days after inoculation there was hyperemia, edema and swelling of tubular epithelium; leptospires were detected intravascularly, in interstitium and embedded within basement membranes. At day 7, leptospires were at basal surfaces of proximal tubules and in phagosomes in tubular epithelium. Perivascular aggregates of monocytes and macrophages were prominent. At day 14, intersitial cells were chiefly plasmacytes and lymphocytes. Leptospires were only on tubular epithelial cell surface microvilli. In another experiment, all pigs receiving low-virulent strains had leptospires in the renal interstitium at 7 days after inoculation but had none at 14 days. All low-virulent strains produced degenerative changes and lymphocyte-plasmacytic infiltration. These studies indicate that non of the low-virulent isolates were acceptable for use in vaccines. Fialure of leptospires to remain attached to microvilli of proximal tubules in late stages of acute infection may be related to differences in virulence of various isolates.