Luciana M. Silva

Chemotherapeutic effects on larval stages of Schistosoma mansoni during infection and re-infection of mice

The sensitivity of the larval stages of Schistosoma mansoni to chemotherapy with praziquantel and oxamniquine was tested in mice during primary and secondary infections and after different intervals from cercarial exposure. Worm recovery by perfusion of the porto-mesenteric system, followed by counting and a morphometric study of the parasite, allowed the conclusion that the relative resistance of the larval stages of S. mansoni to schistosomicide drugs, demonstrated in primary infections, also persists when the host is already infected. This indicates that a therapeutic failure may result when an infected host is treated some time after being re-infected, because of the presence of migrating, drug-resistant, immature forms of the parasite.

Pathogenesis of schistosomal ‘pipestem’ fibrosis: a low-protein diet inhibits the development of ‘pipestem’ fibrosis in mice

Mice maintained on a low protein diet for 30 days and then infected with Schistosoma mansoni for 16 weeks completely failed to develop ‘pipestem fibrosis’ of the liver, whereas 50% of well nourished controls did. Usually mice with relatively mild and prolonged S. mansoni infection develop two different pathological pictures: one consisting of disseminated portal fibrosis caused by periovular granulomas concentrated at the portal spaces (pipestem fibrosis), the other represented by scattered hepatic granulomas. The reason for this dual response is poorly understood. Combined results from parasitological, histopathological, biochemical and morphometric data revealed that peri‐ovular granulomas of undernourished mice were smaller, inflammation was less intense and there was minimal fibrosis in comparison with those of controls, which suggest that a vigorous host response is necessary for the pathogenesis of schistosomal portal fibrosis.

Decreased humoral and pathologic responses in undernourished mice infected with Schistosoma mansoni

We previously demonstrated that mice subjected to a hypoproteinic diet showed milder chronic lesions on infection with Schistosoma mansoni than normally fed mice. Here we compare the immune response of well-nourished and undernourished mice with chronic S. mansoni infection. The proliferative response and cytokine (IFN-γ and IL-5) production of splenocytes from undernourished mice against the soluble egg antigen (SEA) of S. mansoni or concanavalin A was similar to that of well-nourished mice. The levels of SEA-specific IgG1, IgG2b and IgG3 antibodies were significantly higher in the sera of well-nourished mice in comparison with undernourished mice. Undernourished animals also exhibited diminished periovular granuloma size compared to well-nourished infected controls. Our results support the importance of host nutritional status in the humoral immune response of mice and its effects on the development of periovular granulomas in malnourished animals infected with S. mansoni.

Hepatic capillariasis in rats: a new model for testing antifibrotic drugs

Rats infected with the helminth Capillaria hepatica regularly develop septal hepatic fibrosis that may progress to cirrhosis in a relatively short time. Because of such characteristics, this experimental model was selected for testing drugs exhibiting antifibrosis potential, such as pentoxifylline, gadolinium chloride and vitamin A. Hepatic fibrosis was qualitatively and quantitatively evaluated in liver samples obtained by partial hepatectomy and at autopsy. The material was submitted to histological, biochemical and morphometric methods. A statistically significant reduction of fibrosis was obtained with pentoxifylline when administered intraperitoneally rather than intravenously. Gadolinium chloride showed moderate activity when administered prophylactically (before fibrosis had started), but showed a poor effect when fibrosis was well advanced. No modification of fibrosis was seen after vitamin A administration. Hydroxyproline content was correlated with morphometric measurements. The model appears to be adequate, since few animals die of the infection, fibrosis develops regularly in all animals, and the effects of different antifibrotic drugs and administration protocols can be easily detected.

Experimental neuroschistosomiasis: inadequacy of the murine model.

Neuroschistosomiasis is rarely observed in human pathology, but it is of considerable importance. To investigate its pathogenesis, consequences and response to treatment, an experimental model would be desirable, but is not yet available, in spite of a few indications of a suitable mouse model in the literature. Severe, recent and late Schistosoma mansoni infections in outbred and inbred strains of mice revealed widespread distribution of parasite eggs in several organs, but only exceptionally did eggs reach the encephalus, thus revealing the inadequacy of the mouse as an experimental model for neuroschistosomiasis.

Immunostimulation as adjuvant for the chemotherapy of experimental schistosomiasis.

Immunosuppressed animals respond poorly to schistosomal chemotherapy and a proper response can be restored by the administration of immune serum. Present study attempts to search whether immunological stimulation would increase drug effectiveness. Swiss mice infected with 50 S. mansoni cercariae were later treated with complete Freunds adjuvant. Treatment with oxamniquine was made with 100 mg/kg.b.w., 25 mg/kg.b.w. and 50 mg/kg.b.w., the last two doses representing a fourth and a half of the recommended curative dose. Appropriate controls for the drug, the adjuvant and the infection were also studied. The serum-level of anti-S. mansoni antibodies (ELISA) and recovery of worms by perfusion of the portal vein system were the evaluated parameters. Statistical analysis of the results failed to reveal significant differences in worm recovery between adjuvant-stimulated animals treated with oxamniquine and any of the treated controls receiving the same amount of the drug. Although total lack of immunity interferes with curative treatment the usual immune response seems to be sufficient to allow for curative drug action in schistosomiasis and thus apparently does not need to be artificially stimulated.

Primary culture of Rhodnius prolixus (Hemiptera: Reduviidae) salivary gland cells

In the present paper, we developed a primary culture of Rhodnius prolixus salivary gland and main salivary canal cells. Cells remained viable in culture for 30 days. Three types of cells were indentified in the salivary gland cultures, with binuclear cells being the most abundant. The supernatants of salivary cultures contained mainly 16-24 kDa proteins and presented anticoagulant and apyrase activities. Secretion vesicles were observed budding from the cellular monolayer of the main salivary canal cells. These results indicate that R. prolixus salivary proteins may be produced in vitro and suggest that the main salivary canal may have a possible secretory role.

Repair of schistosomal intestinal vascular lesions after curative treatment

The process of repairing intestinal vascular lesions induced by schistosomiasis in mice was studied before and after curative chemotherapy, by means of histopathology coupled with injections of the mesenteric veins with India ink or plastic, in this case followed by corrosion in strong acid. The granulomas were avascular, mainly formed while within blood vessels, and were associated with distortion of the intestinal vasculature in their proximity, represented by tortuosities, focal dilatation, narrowing, and anastomosis of the mucosal and submucosal veins. Two to four months after cure of schistosomiasis involuting granulomas were seen to be slowly vascularized, a process going from the periphery toward the center of the granulomas. No intravascular granulomas were seen four months after treatment. The previously distorted mucosal and submucosal veins gradually regained their normal appearance, only a slight tortuosity remaining.