Cercaria of Schistosoma
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| Year of publication | 2016 |
| Type | Chapter of a book |
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| Citation | |
| Description | Cercaria of the genus Schistosoma represents a free-swimming developmental stage that to complete its life cycle must contact the mammalian skin. Thereafter, it penetrates the skin and transforms into an intravertebrate stage – the schistosomulum. Therefore, the cercaria represents an infective stage, a link between the intermediate (snail) and the definitive (mammal) hosts. The cercaria lives for only a brief time in fresh water; it apparently does not feed and if it fails to rapidly penetrate the host and continue development its stored energy resources become exhausted and it dies (Coles 1972; Dorsey et al. 2002; McKerrow et al. 2006). The following account of the morphology and ultrastructure of the cercaria of Schistosoma is based on a high number of fundamental historical works, such as those written by, e.g., Morris (1971), Yamaguti (1971), Stirewalt (1974), Samuelson and Caulfield (1985). Among recent contributions in the field it is necessary to mention comprehensive works of Dorsey et al. (2002) and Collins et al. (2011). In addition to outlining the morphology and anatomy, this chapter investigates dispersal of cercariae and selection of the definitive host, temporal correlation with the host activities, shedding (emergence) from the snail intermediate host, longevity and infectivity of cercariae, behavior after contact with the host and the penetration process as the key point in host invasion. Many of the processes mentioned above are dependent on the action of molecular factors produced by cercariae; therefore, the data on important proteins, saccharides and other substances and their expression in the cercarial body will also be presented. Origin of the cercaria from the sporocyst is briefly discussed by Yoshino et al. (Chapter 7) and its transition into the schistosomulum by Gobert and Nawaratna (Chapter 9). |
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