Ebook Textbook of medical parasitology (6th edition): Phần 2
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Ebook Textbook of medical parasitology (6th edition): Phần 2
CHAPTER 9Trematodes: Flukeslennalodes are unsegnienled helminths which are flat and broad, resembling I he leal ol a tree or a llatlish (hence the nam Ebook Textbook of medical parasitology (6th edition): Phần 2me Finke, Irom the Anglo-Saxon word Hoc meaning llatlish). The name Trematode comes Irom their having large prominent suckers with a hole in the middle (Cireek trema—hole, eillos—appearance).I hey vary in size from the species just visible Io the naked eye, like I It’teropln/es to the large lleshy H Ebook Textbook of medical parasitology (6th edition): Phần 2ukes, like Fasciola and Fasciol opsis. Medically important members ol the class Trcmatoda belong to the subclass Digcnca, as they are digcnctic, i.e.Ebook Textbook of medical parasitology (6th edition): Phần 2
require two hosts. I he definitive hosts in which they pass the sexual or adult stage are mammals, humans or animals, and the intermediate hosts in whCHAPTER 9Trematodes: Flukeslennalodes are unsegnienled helminths which are flat and broad, resembling I he leal ol a tree or a llatlish (hence the nam Ebook Textbook of medical parasitology (6th edition): Phần 2 lor schistosomes ill which the sexes arc separate (Fig. 9.1).A conspic uous feature is the presence of two musc ular cup-shaped suckers (henc e called Distomata)—the mill sucker surrounding the mouth al the anterior end and the veulral suckei or acetabulum in the middle, ventrally. The body is cove Ebook Textbook of medical parasitology (6th edition): Phần 2red by anFIGURE 9.1: Morphology of a hermaphroditic trematode-1. Oral sucker 2. Pharynx 3. Genital pore 4 Ventral sucker 5. uterus 6. Caecum 7. CirrusEbook Textbook of medical parasitology (6th edition): Phần 2
8. Ovary 9. Flame cell 10. Testis 11. Excretory bladderTre mat odes : Fl likes117integument which often bears spines, papillae or tubercles. They havCHAPTER 9Trematodes: Flukeslennalodes are unsegnienled helminths which are flat and broad, resembling I he leal ol a tree or a llatlish (hence the nam Ebook Textbook of medical parasitology (6th edition): Phần 2 the oesophagus which bifurcates anterior to the acetabulum to form two blind caeca, which reunite in some species. The alimentary canal therefore appears like an inverted Y. The anus is absent, the excretory system consists ot flame cells and collecting tubules which lead to a median bladder openin Ebook Textbook of medical parasitology (6th edition): Phần 2g posteriorly. There is a rudimentary nervous system consisting of paired ganglion cells. The reproductive system is well-developed. The hermaphroditiEbook Textbook of medical parasitology (6th edition): Phần 2
c flukes have both male and female structures so that self-fertilisation takes place, though in many species cross-lertilisation also occurs. In the sCHAPTER 9Trematodes: Flukeslennalodes are unsegnienled helminths which are flat and broad, resembling I he leal ol a tree or a llatlish (hence the nam Ebook Textbook of medical parasitology (6th edition): Phần 2rface of the male, which forms the gyiuieivphoric canal.Trematodes arc oviparous and lay eggs which arc opcrculatcd, except in the case ol schistosomes. The eggs hatch in water to form the lust stage larva, the motile ciliated ntirut idtum ((keek miracidiitm—a 'little boy'). I be miracidium infects Ebook Textbook of medical parasitology (6th edition): Phần 2the intermediate host snail in which further development lakes place, the miracidium sheds its cilia and becomes the sac-like sporocyst (meaning a 'blEbook Textbook of medical parasitology (6th edition): Phần 2
adder containing seeds'). Within the sporocyst, certain cells proliferate to form the germ balls, which are responsible for asexual replication. In scCHAPTER 9Trematodes: Flukeslennalodes are unsegnienled helminths which are flat and broad, resembling I he leal ol a tree or a llatlish (hence the nam Ebook Textbook of medical parasitology (6th edition): Phần 2ut in the hermaphroditic trematodes, the sporocyst matures into a more complex larval stage name redia (alter the 17tli century7 Italian naturalist Francesco Redi), which produce cercariae. Cercariae are tailed larvae and hence their name ((keek krrktfs—tail), hl schistosomes, cercariae have a forke Ebook Textbook of medical parasitology (6th edition): Phần 2d tail and infect the definitive host by direct skin penetration, hi the hermaphroditic Hukes, the cercariae have an unsplit tail, and they encyst onEbook Textbook of medical parasitology (6th edition): Phần 2
vegetables or within a second intermediate host, fish, or crab, Io form the metacenariae, which are the infective forms, infection is acquired by ingeCHAPTER 9Trematodes: Flukeslennalodes are unsegnienled helminths which are flat and broad, resembling I he leal ol a tree or a llatlish (hence the nam Ebook Textbook of medical parasitology (6th edition): Phần 2asexual multiplication during larval development is 01 great magnitude, and in some species, a single miracidium may give rise to over half a million cercariae.Trematodes infecting humans can be classified as follows:A.Diecious blood flukes or Schistosomes which live inside veins in various location Ebook Textbook of medical parasitology (6th edition): Phần 2s:1hl the vesical and pelvic venous plexuses—Schistosoma haematobium.2hl the inferior mesenteric vein—s. mansoni3In the superior mesenteric vein—s. ịaEbook Textbook of medical parasitology (6th edition): Phần 2
poHÌciimB.Hermaphroditic flukes which live hi the lumen of various tracts:1Biliary tract (liver flukes); Clonorchis sinensis. Fasciola hepatica. OpislCHAPTER 9Trematodes: Flukeslennalodes are unsegnienled helminths which are flat and broad, resembling I he leal ol a tree or a llatlish (hence the nam Ebook Textbook of medical parasitology (6th edition): Phần 2tits waisonib.Large intestine—Gastrodiscoides hominis3Respiratory tract (Lung fluke)—Paragonimus wester multi.118Textbook of Medical ParasitologySCHISTOSOMES: BLOOD FLUKESSchistosomes are diecious trematodes in which the sexes are separate. The male is broader than the female, and its lateral border Ebook Textbook of medical parasitology (6th edition): Phần 2s are rolled ventrally into a cylindrical shape, producing a long groove or trough called the gynaccophoric canal, in which the female is held. It appEbook Textbook of medical parasitology (6th edition): Phần 2
ears as though the body ol the male is split longitudinally Io produce this canal—hence the name Schistosome (Cireek schisto—split and soma— body). ScCHAPTER 9Trematodes: Flukeslennalodes are unsegnienled helminths which are flat and broad, resembling I he leal ol a tree or a llatlish (hence the nam Ebook Textbook of medical parasitology (6th edition): Phần 2All schistosomes live in venous plexuses in the body of the definitive host, the location varying with the species (big. 9.2).FIGURE 9.2: Morphology of Schistosomes: Male and female in copula. 1. Oral sucker2. Ventral sucker 3. Uterus 4. Gynaecophoric canal 5. Testis 6. CaecumSc histosomes differ fr Ebook Textbook of medical parasitology (6th edition): Phần 2om the hermaphroditic tremakxies in many respects. they lack a muscular pharynx. Then- intestinal caeca reunite alter bilurcation to form a single canEbook Textbook of medical parasitology (6th edition): Phần 2
al. They produce non-operculate eggs. They have no redia stage in larval development, rhe cercariae have forked tails and infect by penetrating the unCHAPTER 9Trematodes: Flukeslennalodes are unsegnienled helminths which are flat and broad, resembling I he leal ol a tree or a llatlish (hence the nam Ebook Textbook of medical parasitology (6th edition): Phần 2lions 01 persons in Africa, Asia and Latin America. It is estimated that over 100 milion persons arc infected with s. haematobium, s. mattsoni and s. jaftoftieum each.SCHISTOSOMA HAEMATOBIUMHistoryThis vesical blood Huke, formerly known as Bilharzia haematobium has been endemic in the Nile valley in Ebook Textbook of medical parasitology (6th edition): Phần 2 Egypt for millenia. Its eggs have been found in the renal pelvis of an Egyptian mummy dating from 1250-1000 B.c. Schistosome antigens have been identEbook Textbook of medical parasitology (6th edition): Phần 2
ified by ELISA in Egyptian mummies of the Predynastic period, 3100 B.c. The adult worm was described in 1851 by Bilharz in Cairo. Its life cycle, inclCHAPTER 9Trematodes: Flukeslennalodes are unsegnienled helminths which are flat and broad, resembling I he leal ol a tree or a llatlish (hence the nam Ebook Textbook of medical parasitology (6th edition): Phần 2nched in the Nile valley, s. haematobium is also endemic in most parts ot Africa and in West Asia. An isolated locus oi endemicity in India was identified in Ratnagiri, south OÍ Mumbai by Gadgil and Shah in 1952. Ebook Textbook of medical parasitology (6th edition): Phần 2CHAPTER 9Trematodes: Flukeslennalodes are unsegnienled helminths which are flat and broad, resembling I he leal ol a tree or a llatlish (hence the namGọi ngay
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