Schistosoma mansoni: avaliação da fibrose hepática em camundongos submetidos quimioterapia e reinfectados / Schistosoma mansoni: assessment of hepatic fibrosis in mice undergoing chemotherapy and reinfected

A esquistossomose mansônica é uma doença parasitária tropical. Causadas por helmintos do gênero Schistosoma. Com a intenção de conter a doença, diversos institutos e organizações vêm desenvolvendo medidas de controle para tratar indivíduos infectados e evitar a ocorrência de novas infecções. Estratégias de administração de medicamentos em massa são eficazes na cura da doença, entretanto o tratamento com drogas anti-helmínticas não previnem a possibilidade da ocorrência de reinfecções. Diante desta questão, neste trabalho propusemo-nos a analisar a cinética da fibrose hepática em camundongos esquistossomóticos tratados e submetidos à reinfecção. Para alcançar este objetivo, 70 camundongos Swiss foram infectados com 50 cercárias de S.mansoni, posteriormente tratados com Oxamniquine ou Praziquantel e reinfectados quatro meses após tratamento. Os fígados destes animais foram submetidos a técnicas de imunohistoquímica e imunofluorescência e microscopia eletrônica de transmissão para avaliação da expressão e participação de componentes envolvidos no processo fibrogênico. Para verificar os índices de colágeno entre os grupos utilizou-se a análise morfométrica. A análise histológica revelou que camundongos esquistossomóticos submetidos à quimioterapia específica desenvolveram altos índices de fibrose durante a reinfecção. A imunomarcação para alfa actina de músculo liso (α-SMA) revelou que grande parte do parênquima hepático dos animais tratados e reinfectados exibiam células com perfil miofibloblástico. A imunofluorescência demonstrou que o padrão de marcação para laminina estava alterado em animais com esquistossomose. A análise morfométrica revelou que reinfecção destes animais ocasionou uma intensa deposição de fibras colágenas no parênquima hepático. Os dados obtidos demonstraram que a reinfecção em animais previamente tratados, foi capaz de induzir uma resposta fibrótica semelhante a encontrada nos animais com infecção primária.

Susceptibility and resistance to Schistosoma mansoni reinfection: parallel cellular and isotypic immunologic assessment.

Cellular and humoral immune responses to Schistosoma mansoni antigen preparations were evaluated in individuals presumed to be susceptible or resistant to reinfection after chemotherapeutic cure. A consistent proliferative increase in the response to soluble egg antigen (SEA) was observed post-treatment in both the susceptible and resistant groups. However, this change was not related to resistance. Isotype studies showed that IgM antibody levels to soluble worm antigen preparation (SWAP) and cercariae antigens were significantly higher in the resistant group than in the susceptible group. Post-treatment, an increase in IgE anti-SWAP and anti-schistosomular tegument (STEG) responses and a decrease in IgG4 anti-SEA and anti-STEG responses were observed in the resistant group. These finding are similar to those we have reported previously for a putative resistant group termed endemic normals, and are compatible with immunologic studies in different endemic areas. Together, these findings indicate that even on the population level, high IgE specificities coupled with low IgG4 specificities correlate well with documented resistance to reinfection.

[Measures for control of schistosomiasis adopted by the National Health Foundation]. / Medidas de controle.

The control measures used by the Ministério da Saúde/Fundação Nacional de Saúde for 1990/1991, started to have a new focus when significant advances were evidenced in the two last decades and after internal meetings with participation of the scientific community interested in accompanying the actions directed to the control of schistosomiasis in our country. Since then, the priority started to be the suppressing of the occurrence of advanced clinical forms, having as an objective, the detection and treatment of all carrier of Schistosoma mansoni. Beyond the control measures, factors that may interfere in the application of those measures were also studied, the diverse phases of field operations, the work methodology and results obtained in the first semester of 1991.

Schistosomiasis in a mining area: intersectoral implications.

The high prevalence (greater than 90%) and intensity of infection (50% of those infected excreted greater than 600 eggs per gram of faeces) of schistosomiasis in a tin mining area in eastern Zaire is related to extensive man-made ecological changes and intensive man/water contact. Construction of latrines, water supply and availability of diagnosis and treatment through occupational health services have been used in control efforts. The integration of environmental measures is limited by their high costs. The control of schistosomiasis in this area of intense transmission would require repetitive chemotherapy and other measures which are beyond available resources.

Cost-effectiveness of different ways of controlling intestinal schistosomiasis: a case study.

Intestinal schistosomiasis is highly prevalent among the labourers and their families in many of the miners' villages in Maniema, Zaire. Following treatment, a quick re-infection can be observed if no measures are taken to reduce transmission. It is shown that the rate of re-infection is reduced when the water bodies around an endemic village are properly molluscicided. When, in addition to chemotherapy, a strategy of focal mollusciciding was adopted beneficial effects were visible 12 months after treatment but no longer at 20 months. In view of the comparatively small size of the human populations in the endemic villages, and due to the extent and the variety of the snail-infested water bodies, chemotherapy only, without additional measures, would seem to be the most cost-effective type of control, under the prevailing conditions. This conclusion should be revised when long term health-planning could be effectively envisaged for the area.

Schistosoma mansoni control in Cul de Sac Valley, Saint Lucia. II. Chemotherapy as a supplement to a focal mollusciciding programme.

After an intensive area-wide mollusciciding campaign, over four and a half years, transmission of Schistosoma mansoni was reduced. A cheaper scheme suitable for the follow-up or consolidation stage of control was evaluated and two selective population chemotherapy campaigns using hycanthone (2 mg/kg b.w.) and oxamniquine (15 mg/kg b.w.) were mounted. Prevalence dropped to 6% and 3% in areas with previously high and low levels of transmission respectively. Calculations suggested that these figures were falsely low and that perhaps 20% of the population were still excreting S. mansoni ova in small numbers. The unco-operative groups in the population are probably more important in maintaining a reservoir of infection in the community than persons with light infections undetected by the sedimentation concentration stool examination technique used. The benefit of more sensitive but more costly examination techniques is not clear since the importance of very light infections in transmission is uncertain. Case detection absorbs an increasing proportion of the total cost of chemotherapy programmes with fewer cases being found amongst the same number screened. Using hycanthone (649 treated) the cost per person protected was $0.74 and using oxamniquine (264 treated) $0.94. The need to develop low cost consolidation or follow-up procedures for preventing a resurgence of transmission after successful control, when the infection is no longer of public health importance, is stressed.

Control of Schistosoma mansoni transmission by chemotherapy in St. Lucia. I. Results in man.

Control of Schistosoma mansoni transmission solely by treatment of all infected persons was attempted in Marquis Valley (population about 3,100), St. Lucia. Two-year results are reported. Excluding 26 pregnant patients, 709 to 729 persons who were found to be infected received treatment the first year. Most of these, 677, were given a single injection of hycanthone (2.5 mg/kg of body weight), and the same treatment was administered to 159 patients the second year. Side effects were not severe; the major side effect, vomiting, occurred in about 22% on both occasions. In villages with initially high transmission rates, the incidence of new infections in children 0 to 14 years fell from 20.8% before chemotherapy to 7.4% after 1 year and to 3.7% after 2 years. This pattern was significantly different from that in the comparison area where no control scheme exists. Chemotherapy alone appears to be a rapid, effective, and comparatively inexpensive method of controlling S. mansoni transmission in St. Lucia.