PATHOGENICITY OF Blastocystis sp. TO THE GASTROINTESTINAL TRACT OF MICE: RELATIONSHIP BETWEEN INOCULUM SIZE AND PERIOD OF INFECTION

Abstract

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.

Preneoplastic proliferative changes induced by experimental blastocystosis

“…Thus, caution should be observed when choosing a suitable animal model to study blastocystosis. In our animal experimental study, and as previously reported [28,29,43,44] , 3 weeks-old mice were used successfully to produce blastocystosis. All Blastocystis spp.…”

“…In the present work, experimental blastocystosis was successfully induced in all BALB-c mice by intragastric inoculation with 1.0×10 5 Blastocystis organisms in100 μl saline. In the work of El Wakil and Hewedy [28], similar inoculum doses produced infection in only 40% of the animals while in the work of Pavanelli et al [44] , a smaller inoculum of 1.0 x 10 2 produced infection in all animals. These variations may be due to differences in infectivity of Blastocystis spp.…”

“…Similarly, in the present work in sections of the large intestine of mice in GI (4/7 mice) and GII (2/6 mice), only the lamina propria appeared to be invaded by the vacuolar forms. Invasion of the lamina propria, submucosa and reaching up to the muscular layer of the intestine by vacuolar forms was seen only with high infective doses [28,44] , demonstrating the impact of the higher dose of inoculum. Vacuolar forms of Blastocystis spp.…”

“…Positive stools examinations of mice began from 4 to 6 days PI in the three groups. Earlier diagnosis of infection of 2 to 5 days [28,44] in mice, and 3 to 4 days [6] in rats were reported depending on the inoculum size.…”

“…A similar picture with mild inflammatory reaction was noticed in mice inoculated by isolates derived from asymptomatic carriers included in our study. On the other hand, isolates from symptomatic patients have been observed, in many studies, to cause more severe and intense pathological changes with mucosal sloughing, intense inflammatory cells infiltration, and parasite infiltration of lamina propria in mice [28,30,44,49] and rats [6,27,31,55] . In addition, Hussein et al [31] and Abaza et al [6] reported the induction of a more severe degree of pathological change with polypoid projections in colonic mucosa of rats infected by symptomatic isolates, that the authors referred to as precancerous polyps.…”