Résistance a la dessiccation de Biomphalaria glabrata adultes infestés par plusieurs miracidiums de Schistosoma mansoni / Resistance to desiccation of Biomphalaria glabrata adults by polyinfection of Schistosoma mansoni miracidia

1200 adult Biomphalaria glabrata were submitted during 6 weeks to anhydrobiosis condition. Some snails were health, some were previously infected 3 days or 12 days ago with 8 ñ 2 miracidia of Schistosoma mansoni, others were shedding cercariae . The snails were put on soil or buried into hermetically closed, or ventilated, plastic boxes. There was no survival of snails kept in sealed boxes, or among positive snails, but 44% of control health snails and 40,6% of infected (for 3 or 12 days) snails in ventilated boxes were living at the term of the desiccation stage. Survival was better for "on soil" snails than for "buried" snails, but difference was shown between 3-days and 12-days infection. The surving desiccated B. glabrata had a lesser death rate and a lesser cercarial production than infected snails kept in water. An inferior production of male cercariae comparatively to female and to "mixed" cercariae was demonstrated by statistical analysis of the cercarial sheddings. In all positive snails, periodic variations of cercarial production was shown, whatever the sex of those cercariae. In addition many pauses of the sheddings were established by the authors

[Resistance to desiccation of Biomphalaria glabrata adults infested by various miracidia of Schistosoma mansoni]. / Résistance á la dessiccation de Biomphalaria glabrata adultes infestés par plusieurs miracidiums de Schistosoma mansoni.

1200 adult Biomphalaria glabrata were submitted during 6 weeks to anhydrobiosis condition. Some snails were healthy, some were previously infected 3 days or 12 days ago with 8 +/- 2 miracidia of Schistosoma mansoni, others were shedding cercariae. The snails were put on soil or buried into hermetically closed, or ventilated, plastic boxes. There was no survival of snails kept in sealed boxes, or among positive snails, but 44% of control healthy snails and 40.6% of infected (for 3 or 12 days) snails in ventilated boxes were living at the term of the desiccation stage. Survival was better for "on soil" snails than for "buried" snails, but no difference was shown between 3-days and 12-days infection. The surviving desiccated B. glabrata had a lesser death rate and a lesser cercarial production than infected snails kept in water. An inferior production of male cercariae comparatively to female and to "mixed" cercariae was demonstrated by statistical analysis of the cercarial sheddings. In all positive snails, periodic variations of cercarial production was shown, whatever the sex of those cercariae. In addition many pauses of the sheddings were established by the authors.

[The influence of anhydrobiosis on the infestation of Biomphalaria glabrata by Schistosoma mansoni miracidium]. / Influence de l'anhydrobiose sur l'infestation de Biomphalaria glabrata par un miracidium de Schistosoma mansoni.

410 Biomphalaria glabrata (Caribbean strain of Guadeloupe) have been infected with one miracidium of Schistosoma mansoni, 110 snails, used as controls have been kept into water; the survival rate was 96.4% after 4 weeks and 25.4% produced cercariae. 300 snails were kept on wet soil, and submitted for 6 weeks to progressive desiccation. The survival rate was 23.4% but only 9 of them produced cercariae. Periodic variations of the production of male and female larvae have been shown by the weekly test of the cercariae productions. In previously desiccated snails, the production of male and female cercariae is similar while in controls the production of female larvae is more important. In experimental snails, the larval development seems to be stopped during anhydrobiosis. The production of cercariae is just delayed for the length of the dry keeping.

Weight loss and survival of Biomphalaria glabrata deprived of water.

Immature and mature Biomphalaria glabrata are kept out of water at relative humidities varying from 0 to 100%. When snails are submitted to a saturated atmosphere, they show a slow weight loss and survival may be long. If relative humidity (RH) decreases, weight loss becomes important and survival is short. A reduced RH (0 to 65%) produces similar effects. During desiccation, fasting has no noticeable effect; survival depends essentially on weight loss.