Mechanism of Attraction and Penetration of Schistosoma Mansoni Cercariae Into Mammalian Skin.

Abstract

Cercariae showed a progressive decline in their capacity to penetrate excised mouse abdominal skin from previously uninfected BALB/c mice that ranged from 31.1% in 1 week old animals to 9.8% in one year old mice. The most dramatic decline in penetration occurred within the first 4 weeks of age. The percentage of cercariae that were attracted to and penetrated into the skin also declined with age; 95.1% penetrated into 3 week old mice compared to 90.9% in 6 month old mouse skin (p < .001). Selective alteration of the basement membrane in excised mouse abdominal skin from 8 month old mice by trypsin treatment resulted in increased cercarial penetration of 24.1% (untreated controls = 9.2%, p < .001) to a level comparable to untreated 3 week old mice of 28.2%. Mice placed on a lathyrogenic diet of showed a significant increase in cercarial penetration through excised mouse skins compared to controls (44.6% vs 25.4%, p < .001). These results suggest that alterations in collagen molecules with age in the skin basement membrane impair cercarial penetration. Age-related changes in skin surface lipids might also contribute to a decline in cercarial penetration with age. Gas-liquid chromatographic analysis of skin surface lipids showed a greater proportion of potent stimulants of cercarial penetration in young mice compared to older mice. Mice placed on an essential free fatty acid deficient diet that altered the amount of unsaturated free fatty acids stimulatory to cercariae showed a significantly decreased cercarial penetration compared to controls (25.2% vs 36.9%, p < .02).</p> Cercariae were found to be attracted to bicarbonate ions in the underlying media of the penetration chambers. Attraction to bicarbonate ions was a stronger stimulus than a temperature differentiated environment. Other major components in human sweat failed to attract cercariae. Pure lipid st and ards of free fatty acids found in skin surface lipid were evaluated for their ability to stimulate cercariae to either penetrate into agar, release their preactabular gl and contents or stimulate increased cercarial activity. Docosahexaenoic acid was the most potent stimulus for cercarial penetration into agar and linolenic acid the most potent stimulus for preactabular gl and release. Both compounds were significantly more potent stimuli in all three types of cercarial behavior than other free fatty acids tested. More highly unsaturated free fatty acids were generally more potent stimuli, although position of the double bonds in the free fatty acids was also important. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI