Worms flatworms

Parasitic stages, on the other hand, generally do not use oxygen as the final electron acceptor but use fermentative processes to obtain most of their ATP. For these stages, an uneconomical energy metabolism is not detrimental, as the host provides the nutrients. Most adult flatworms inside the final host produce end products of a fermentative carbohydrate breakdown, such as succinate, acetate, propionate and lactate. These end products are formed via malate dismutation, a fermentative pathway, which is present in all types of parasitic worms (flatworms as well as many nematodes), but which is also present in animals like freshwater snails, mussels, oysters and other marine organisms. Malate dismutation is linked to a specially... 

Flatworms (platyhelminths) tape worms (cestodes) flukes (trematodes) e.g.. Schistosoma species (bilharziasis) praziquantel praziquantel... 

The body of flatworms (phylum Platyhehninthes) consists of two external cell layers (endoderm and ectoderm) with a third layer between. A distinct excretory system is present. In addition to a nerve net resembling that of the Cnidaria, there are a cerebral ganglion and distinct eyes. One large group of flat-worms, the planaiians (typically about 15 mm in length, Fig. 1-14), inhabit freshwater streams. They are said to be the simplest creatures in which behavior can be studied. 

Many parasitic flatworms (tapeworms and flukes) attack higher organisms.124 Among them are the Schistosoma, tiny worms that are transmitted to humans through snails and which attack the blood vessels. The resulting schistosomiasis is one of the most widespread debilitating diseases on earth today, affecting 200 million people or more.125126... 

A review of platyhelminth genomes written just 10 years ago would have painted a very different picture to the one which we can write today and we would never then have predicted that we would be in the position that we currently find ourselves in, with full genome sequencing projects underway for several flat-worm species. Even if one s scientific interest falls outside the currently targeted species, these efforts should not just be viewed as stamp collecting they are revealing fundamental information of potential interest and value to the entire flatworm research community. Moreover, the methods of analysis are... 

Briefly, the flatworm brain is most commonly a ring-like or semicircular structure formed by the connection of two concentrations of nerve axons and nerve cell bodies by a well-developed commissure or commissures. These bilobed accumulations of nerves form the cerebral ganglia that occupy the lateral margins of the brain and comprise a core of nerve axons that are enveloped by a loose gathering of the associated cell bodies at least some flat-worm brains appear to be further surrounded by multilayer sheaths of mesenchyme that represent primitive glia-like cells (Sukhdeo and Sukhdeo, 1994). 

Unlike the situation in nematodes and arthropods, where hundreds of neuropeptides have been elucidated using biochemical, physiological and molecular techniques, flatworm neuropeptide discovery is still in its infancy. This is despite the characterization of the first flat-worm neuropeptide almost 15 years ago (Maule et al., 1991). Progress has been hindered by the inability to obtain large quantities of flatworm neuronal tissues and the absence, until recently, of a significant body of genomic and/or EST data for flatworms. Nevertheless, the available evidence does provide a snapshot of what appear to be the most abundant and widespread flatworm neuropeptides. 

Very little is known about lipid metabolism in parasites, although in several aspects, it is quite different from that of the mammalian host. Lipids, like phospholipids, triacylglycerols and cholesterol, are not synthesized de novo by parasitic flatworms, but are obtained directly from the host (cholesterol) or are synthesized from building blocks obtained from the host (fatty acids and in case of phospholipids, also the head groups). A schematic and partly hypothetical overview of the main pathways of lipid metabolism in parasitic flat-worms is shown in Fig. 20.3. Fatty acids are... 

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