Mice infected with about 90 cercariae of Schistosoma mansoni (LE strain) were treated during five consecutive days with dexamethasone (50 mg/Kg, subcutaneously), starting on the 42th day of infection. Groups of five mice were then daily sacrificed from the first day after onset of treatment until the first day after. The perfusion of the portal system was performed and a piece of the intestine was processed for qualitative and quantitative oograms. This treatment carries to larger numbers of eggs in the tissues of treated mice, when compared with untreated groups. No changes were observed in the kinetics of oviposition, as all stages of viable eggs were observed in the tissues of treated and control mice. These data reinforce the hypothesis of a partial blockade of the egg excretion in immunossupressed mice.

Cercárias de Schistosoma mansoni, inoculadas na cavidade peritoneal de camundongos da linhagem AKR/J, conseguiram sobreviver in situ e chegar à maturidade sexual. Ao contrário da linhagem convencional (SWISS), onde as fêmeas que se desenvolveram no peritônio não produziram ovos, 7,7% das fêmeas retiradas da cavidade peritoneal de camundongos AKR/J apresentavam ovo normal no útero. Os parasitos recuperados da cavidade peritoneal de ambas as linhagens não apresentaram pigmento hemoglobínico, indicando que os mesmos sobrevivem na cavidade peritoneal de camundongos sem a necessidade de ingestão de hemácias. O desenvolvimento do parasito na cavidade peritoneal de camundongos AKR/J, com produção de ovos normais, reforça os dados, já existentes na literatura, que mostram que o ciclo evolutivo do parasito pode ser completado sem a necessidade da fase pulmonar.

Morphometric analysis of Schistosoma mansoni male worms obtained from AKR/J and Swiss mice was carried out. Rodents infected by the intraperitoneal route with 80 cercariae of the schistosome (LE strain) were killed by cervical dislocation at 45 and 60 days post-infection and both peritoneal lavage and perfusion of the portal system were performed for the recovery of adult worms. Characteristics including total body length, the distance between oral and ventral suckers, extension of testicular mass and the number of testes were considered in the morphological analysis. Changes that occurred in S. mansoni recovered from the peritoneal cavity or from the portal system of AKR/J and Swiss mice included total body length and reproductive characteristics. Significant morphometric alterations were also observed when worms recovered from the portal system of both strains of mice were compared with the schistosomes obtained from hamsters (Mesocricetus auratus), the vertebrate host in which the LE strain had been adapted and maintained by successive passages for more than four decades. The present results reinforce the idea that S. mansoni has high plastic potential and adaptive capacity.

The schistosome oviposition and granuloma constitution in the peritoneal cavity of AKR/J mice were evaluated. Groups of mice intraperitoneally infected with cercariae of Schistosoma mansoni were weekly euthanized during the acute (56 to 84 days post-infection (DPI)) and chronic (147 to 175 DPI) phase of infection. Schistosome developmental stages obtained via peritoneal lavage and perfusion of the portal system were inspected, counted and fixed, and peritoneal granulomata were then processed for histology. The morphological characterization and quantitative analysis of peritoneal schistosome eggs and granulomata were for the first time performed, such as the demonstration of the viability of miracidia obtained there from. Eutopic and ectopic mature schistosomes and normal pattern of worm oviposition were observed in all periods studied. However, the size of schistosome eggs from peritoneal cavity was smaller than observed for eggs laid by female worms from the portal system. The numbers of S. mansoni eggs and/or granulomata recovered from the peritoneal cavity was higher in chronic than acute infection, while the mean diameter of peritoneal chronic granulomata was smaller than for peritoneal acute granulomata. The constitution and evolution of these cellular reactions at histology were similar to that of hepatic granuloma, and peritoneal granulomata were subject to the host immunomodulation. In addition to the standardization of this experimental approach, which allows the obtaining of free schistosomal granulomata from peritoneal cavity of AKR/J mice, the potential use of these granulomata in ex vivo and in vivo studies is discussed.

The present study aims to elucidate in a sequential manner the changes of the blood coagulation process at different phases of experimental schistosomiasis, comprising the pre-patent, acute, intermediate and chronic phases, and the effect of chemotherapeutic cure, at the acute and chronic phases, on reversion of changes related to the coagulation factors. Mice were infected with Schistosoma mansoni cercariae, and were divided into four groups. Blood samples from these groups were collected 32, 70, 100, and 140 days after infection, corresponding to the pre-patent, acute, intermediate and chronic phases, respectively. Simultaneously, other infected groups were given oxamniquine, 70 and 140 days after infection. At the same time as blood collection from infected and/or treated animal groups, other uninfected control animal groups were punctured and maintained under the same conditions as the infected animals. The vitamin-K-dependent clotting factors were found to be more sensitive to infection at different phases, while factors VIII and XI presented hyperactivity. Results obtained 90 days after chemotherapeutic treatment with oxamniquine, administered at the acute and chronic phases, presented noticeable reversion of the main alterations in the coagulation mechanism. The present study provides unquestionable data on the development of hemostatic changes throughout the course of S. mansoni infection.

No abstract

Treatment with dexamethasone (DMS) in the early phases of the experimental Schistosoma mansoni infection causes an indirect effect on the cercaria-schistosomulum transformation process. This is observed when naive albino mice are treated with that drug (50 mg/Kg, subcutaneously) and infected intraperitonealy 01 hour later with about 500 S. mansoni cercariae (LE strain). An inhibition in the host cell adhesion to the larvae, with a simultaneous delay in the cercaria-schistosomulum transformation, is observed. This effect is probably due to a blockade of the neutrophil migration to the peritoneal cavity of mice, by an impairment of the release of chemotactic substances. Such delay probably favors the killing of S. mansoni larvae, still in the transformation process, by the vertebrate host defenses, as the complement system.

In the experimental schistosomiasis mansoni glucocorticoids cause a reduction in the worm burden when administered in the week of infection or, the longest, at the next week. In order to determinate the probable(s) site(s) of reduction of the worm burden, mice were infected with cercariae of LE strain of S. mansoni and dexamethasone was administered daily (50 mg/kg, subcutaneously) starting 1 hour before infection until the eighth day. Mice were sacrificed daily starting on the third day after infection until the ninth day, and schistosomula from lungs were collected. Six weeks after infection, the remaining mice were sacrificed and perfused for adult worm recovery. Analysis of the results showed that the non-treated mice presented larger numbers of lung larvae than the treated ones, and this difference was also found later in the worm burden in the portal system. This difference may reflect the early death of larvae in treated animals, before or after reaching the lungs.