The pathogenic potential of Blastocystis sp. in experimental models
requires further investigation. In this work, the pathogenicity of this parasite in
the gastrointestinal tract of male Swiss mice was evaluated according to the inoculum
size and period of infection. Animals were infected intragastrically, with 100, 500,
1,000, 5,000 and 10,000 Blastocystis sp. vacuolar forms obtained
from a mixture of eight human isolates cultured axenically in Jones' medium. After
seven, 14, 21, 28 and 60 days of infection, the animals were sacrificed and fragments
of the small intestine (duodenum), large intestine, and cecum were subjected to
histopathological analysis. Blastocystis sp. triggered an
inflammatory response in the different tissues analyzed, with a predominance of
mononuclear cells. The parasite was found in the muscular layer of the cecum, showing
its invasive character. Larger inocula triggered inflammatory processes earlier
(seven days) than smaller ones (from 21 days). We conclude that, in the proposed
model, the pathogenicity of Blastocystis sp. isolates that were
studied is related to inoculum size and period of infection.