Immune and pathophysiological responses to different strains of Giardia duodenalis in neonatal mice

Numerous studies have demonstrated various strain differences between Giard ia isolates, but little is known about the immunology and pathogenesis of i nfections. This study aimed to compare host responses to strains of Giardia duodenalis differing in levels of virulence and pathogenicity and, by doin g so, elucidate the mechanisms via which pathogenic strains establish infec tions. Marked differences were found in the infection dynamics, histopathol ogical responses and serum antibody responses of neonatal mice infected wit h either G. duodenalis strain BRIS/83/HEPU/106 (isolated from a human) or B RIS/95/HEPU/2041 (isolated from a sulphur-crested cockatoo, Cacatua galerit a). Infections with the bird strain were more intense (6.7-times greater) a nd persisted longer (by 14 days) than infections with the human strain. The bird strain was more pathogenic and caused greater pathophysiological alte ration to the gut mucosa, including increased villous atrophy, hyperplasia of goblet cells and vacuolated epithelial cells. Mice infected with the bir d strain produced less serum anti-Giardia IgA and IgM, but more total (non- specific) serum IgA than those infected with the human strain of Giardia. T his suggests that avian G. duodenalis strains are infective for mammalian h osts and may contribute to zoonotic infections. Furthermore, infection of m ice with BRIS/95/HEPU/2041 serves as a good experimental model to provide f urther insight into the mechanisms via which G, duodenalis causes disease. (C) 2000 Australian Society for Parasitology Inc. Published by Elsevier Sci ence. All rights reserved.