Rat Model for the Human Intesinal Microsporidian Enterocytozoon bieneusi

It is always an emergency to develop a reliable animal model or an in v i f ro model for the human intestinal microsporidian Enterocytozoon bieneusi in order to assess a large number of drugs for prophylaxis or therapy, to investigate immunological modulation of this infection and to study biochemical and taxonomic characteristics of the parasite. The objective of our study is to establish a convenient adult rodent model of persistent E. bieneusi infection to assess potential anti-microsporidian compounds. The validity of the "Sprague-Dawley adult rats immunosuppressed with corticosteroids model" is supported by : i) it is used for studies of Pneumocystis carinii or cryptosporidiosis infections [1,3], ii) spontaneous microsporidiosis infections occur in several species including small rodents [8,10], microsporidia of genus Encephalitozoon and Nosema infect both human and non human hosts [2], iii) it is easily adaptable in laboratory. MATEFWLS AND METHODS. Fresh stools tiom HIV-infected patients containing microsporidia spores were stored in 2.5% (v/v) potassium dichromate solution at 4 C and concentration of spores was obtained by a new filtration-centrihgation technic. Species identification of microsporidia was confirmed by TEM examination. Immunosuppression was induced by a regimen of 25 mg of hydrocortisone acetate injected subcutaneousely twice a week, 5 weeks before and during 6 weeks after the microsporidia challenge [ 11. Pneumocystosis prophylaxis was assured by administration in drinlung water of trimethoprim (50 mgkg) and sulfamethoxazole (250 m a g ) per day [4]. Four groups of 6 adult male SpragueDawley rats (Janvier, France) were constituted, 6 non immunosuppressed non challenged (NISNC), 6 non immunosuppressed challenged (NISC), 6 immunosuppressed non challenged (ISNC) and 6 immunosuppressed challenged (ISC). Microsporidia inoculation was performed at day 0, by gastric gavage, with a single dose of 4. lo6 spores in 1 ml volume. Spores shedding was evaluated quantitatively by counting spores under 1.000 X magnification on 100 fields, on total stools from each rats collected at days 0, 1,2, 3 and then every 2-3 days until day 40 and stained using : tluorochrome Uvibio stain [13], Weber's modified trichrome stain [6]. For the intestinal idection detection procedure, with rats sacrificed at different times after microsporidia challenge, duodenal and jejunal histological sections and imprints were performed and examined after hematoxylin-eosin and Weber's modified trichrome stairmg. RESULTS AND DISCUSSION. Rats shed spores from days 2 after destat ion but only developed a chronic and asymptomatic parainfection with a weak excretion of spores in feces (Fig. 1). In imprints obtained from all the 6 challenged rats necropsied at day 40 post-inoculation, a few spores of E. bieneusi were observed in the duodenum (2 rats), proximal jejunum (3 rats) or in the 3 different parts of the small intestine (1 rat). In parallel, the study of histological sections, showed, at the same levels, extensive vacuolization in the apical pole of enterocytes. Neither parasites, nor histological lesions were observed in the small intestine of unchallenged control-rats necropsied at day 40. Fig. 1 : Intensity of Enterocytozoon bienezcri spores fecal shedding in experimentally infected Spragpe-Dawley adult rats immunosuppressed (ISC) or not (NISC) by corticotherapy.