【正文】 Cestode parasites (Tapeworms) Medical Parasitology Course Department of Pathogen Biology Shantou University Medical College Jin Liqun 金 立 群 May 2022 Cestodes Platyhelminthes (the flatworms): Class Trematoda (The flukes or trematodes) Class Cestoda (The tapeworms or Cestodes) Characteristics: 1 Adult lives in the intestine of vertebrates. 2 One or two intermediate hosts. 3 Humans may serve as final host or intermediate host (Transport host or Paratenic host) 4 Hermaphroditic. 5 The nutrition of tapeworms is through integument (skin) as they lack digestive tract. Tegument Cestodes ? They have suckers or sucking grooves and teeth that grasp the host (Holdfast ans) ? Behind a short neck are repeated parts of the worm, each containing reproductive structures with eggs and sperm. perit/biology_image_gallery1.htm Strobila ? 1 Tiny scolex ? 2 Strobila which makes up most of the “worm” ? 3 The strobila consists of a linear series of proglottids ? 4 Each mature proglottid carries a set of female and male reproductive ans Classification of cestodes Phylum Platyhelminthes (flatworm) Class Cestoda Two important orders: Order Pseudophyllidea : Spirometra mansoni Diphyllobothrium latum( fish tapeworm) Order Cyclophyllidea : Teania solium (pork tapeworm) Teania saginata (beef tapeworm) Echinococcus granulosus (hydatid worm) The scolex is the part of the worm that anchors it to the intestinal epithelium and prevents that the worm is passed with the digested food. Morphology of tapeworms: The scolex Different types of scolices Some cestodes carry a rostellum which is armed with hooks. Muscular holdfast ans include suckers or acetabula (usually 4 per scolex), weakly muscled grooves (bothria, 2 per scolex). Scolex of Taenia Solium Strobilation ? Strobilation: asexual process of forming segments ? New proglottids are continuously formed in the neck just below the scolex (A) ? Along the length of the worm the proglottids increase in size and maturity, developing ? from premature (B) ? to mature (C) ? to the “gravid” stage (D) ? in which essentially the entire proglottid is filled with the uterus and eggs. The reproductive system ?The female includes a vagina from the genital pore to a seminal receptacle。 an ovary。 a single oviduct, the ootype, the duct from the seminal receptacle. ?The uterus leads from the ootype and may have either an opening or uteropore or end blindly. Proglottids without uteropores detach when gravid. ?The egg is formed in the ootype with the contributions from the ovary and the vitellaria. The male system consists of numerous testes, vasa efferentia from each testis to the sperm duct. The cirrus is surrounded by the cirrus pouch. Most often the cirrus pouch and female vagina enter a mon chamber, the genital atrium, and share a mon opening, the genital pore. Developmental stages ? With very few exceptions vertebrates are the final host harboring the adult tape worms ? Many invertebrates and vertebrates are parasitized as intermediate hosts ? The embryonate egg contains the oncosphere a larva that will perate the intestinal wall after eggs are swallowed by intermediate host ? The oncospheres of eucestoda have three pairs of hooks which makes it easy to identify them Diagram of oncosphere of Hymenolepis diminuta, dorsal view Taeniid eggs. The eggs of Taenia saginata and T. solium are indistinguishable morphologically. The eggs are rounded, 31 to 43 181。m, with a thick radially striated brown shell. Inside each shell is an embryonated oncosphere with 6 hooks. CDC Developmental stages (metacestodes) ? Pseudophyllidean cestodes ? procercoid: in the 1st ? Intermediate host.(at an end there is a cerere=tail with 6 hooklets) ? plerocercoid :The larvae look fairly similar to the adult In the second host ? Cyclophyllidean ? The medically important larvae are ? cysticercoid, ? cysticercus ? and hydatid ? (some of these larvae provided amplification ? （Coenurus=many scolices) (D. latum) (D. latum) (T. solium) (E. granulosus) (Hymenolepis sp.) Differentiation of the two orders (tapeworms) Pseudophyllidea Cyclophyllidea Scolex amp。 holdfast 2 sucking grooves 4 suckers Uterus curved ducts sacklike, without with opening opening Vitelline gland folliclelike, anterior masses, to ovary posterior to ovary Intermediate host 2 1 Egg elliptic, thin shell, spherical, thick an operculum, an egg embryophore, cell and many yolk cells an oncosphere Morphology of adult tapeworm Adult consists of segments (proglottids) 1 Scolex (head) 2 Neck (the region of segment proliferation) 3 Strobila ( A chain of segments behind the neck) Immature segments Mature segments Gravid segments Scolex/neck/ immature proglotid Anterior region of showing the scolex and neck region. The proglottids on the right are immature。 note that the reproductive