The Life Cycle and Pathogenicity of Isospora Suis in Gnotobiotic and Conventionalized Piglets

94 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1982.To study the life cycle and pathogenicity of I. suis infections, young (mostly 2-3 day old) germfree piglets were inoculated orally with 2.4 x 10('5) sporulated oocysts. The effects of a "normal" bacterial intestinal flora on the infection was determined by conventionalization of some germfree piglets with a pathogen-free bacterial preparation. Piglets were killed and necropsied at 3, 4, 5, 6, 8, 9, 10, 11, and 14 days post-inoculation (p.i.). The early stages of the life cycle were studied in four gnotobiotic piglets infected with dosages of up to 5 x 10('7) oocysts and sacrificed and 24 and 48 hours p.i. To study the possible presence of extra-intestinal stages, liver/spleen, and intestinal lymph node homogenates from two infected piglets, killed at 24 and 48 hours p.i., were injected intraperitoneally into two germfree piglets.The results of these studies indicated that I. suis is a true pathogen of swine capable of causing a severe diarrhea associated with marked villous atrophy and necrosis of the intestinal epithelium. The presence of a bacterial flora in I. suis infected piglets markedly increased mortality, but appeared to have little influence on the histopathological changes induced. The lesions were most prominent in the distal half of the small intestine, and coincided with the distribution of the observed developmental stages. The first asexual generation observed at 1-2 days p.i. produced 2-7 merozoites per meront; the second generation at 3-4 days p.i. produced 2-14 merozoites; and the third generation at 4-5 days p.i. produced 4-24 merozoites. Mature sexual stages were most prominent at 5-6 days p.i. The clinical signs and lesions had a biphasic character and were most pronounced at 4-6 and 8-10 days p.i. Oocyst excretion also was biphasic occurring 5-8 and 11-14 days p.i. The piglet which received spleen/liver homogenates excreted oocysts at 11-12 and 16-17 days p.i. of the donor piglets; the piglet receiving intestinal lymph node homogenates excreted oocysts 10-11 days after initial inoculation of the donor piglets.These results were interpreted to indicate an extra-intestinal phase during the I. suis infection in addition to the three asexual and sexual generations observed in the intestine.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD