Cestodes: Introduction to Parasitology PDF

Cestodes LECTURE (3) INTRODUCTION TO CESTODEs 1  Cestodes  Long, segmented and tape-like worms.  They are endoparasitic, adult inhabits small intestine of definitive host. ...

Cestodes LECTURE (3) INTRODUCTION TO CESTODEs 1  Cestodes  Long, segmented and tape-like worms.  They are endoparasitic, adult inhabits small intestine of definitive host.  Some cestodes invade human tissue by their larval stages (tissue tapeworms) ‫ألراجل املتأخر بريف‬ ‫سويل السجني اكن ملط معلوهل ايكو لقو ده‬  Diphyllobothrium mansoni (Spirometra ‫ دقيقة‬can ‫بسبب انان ادته‬ mansoni).  T. solium  Diphyllobothrium latum  Taenia saginata  Diphyllobothrium proliferum  T. multiceps  Echinococcus granulosus  E. multilocularis  Hymenolepis nana  Dipylidium caninum.  H. diminuta 2  Cestodes Man may be infected with the adult tapeworms or Larval stages: Human infection (Definitive Human infection (Intermediate host) with larval host) with adult cestodes cestodes (THD)2 ‫فضيحة اتين ل سويل امللط يف املنصورة مع هايدي بعد فضيحة انان‬  Cysticercus cellulosa of Taenia solium  aenia saginata (Cysticercosis).  aenia solium  Coenurus cyst of Multiceps multiceps (Coenurosis).  Sparganum or plerocercoid larva of  ymenolepis nana Diphyllobothrium mansoni or D. proliferum  ymenolepis diminuta (Sparganosis).  Hydatid cyst of Echinococcus granulosus or E.  iphyllobothrium latum multilocularis (Hydatid disease).  ipylidium caninum  Cysticercoid larva of Hymenolepis nana. 1. Flattened dorso-venterally & vary from few millimeters to several meters in length 2. The body cavity and digestive system are absent. 3. Nutrition: occurs by absorption of nutritive materials from the surrounding medium through the body wall. 4. Excretory system: multiple flame cells, collecting tubules & 4 longitudinal excretory ducts (2 dorsal and2 ventral) running laterally to open in bladder at last segment. 5. Nervous system: multiple central nerve ganglia at the region of the scolex. 6. Tegument Cestodes absorb all the nutrients through their body wall (tegument). Has a protective function. Secretes chemicals that prevent worm digestion by host by inactivation of host digestive enzymes. 3  Cestodes The adult worm is divided into 3 parts:  Variable shapes and it is provided with organs of attachment.  Provided with bothria or suckers as organs of attachment to keep the tapeworm in place.  Two main types of holdfast organs: ❶ 4 cup-shaped muscular suckers, or 4 cup-shaped muscular suckers and a rostellum armed with one or more rings of hooks. 2 elongated shallow grooves or pits. ❷ Region of growth.  Classified acc. to degree of maturity of genital organs into: 1. Immature segments. ❸ 2. Mature segments. 3. Gravid segments. 4  Cestodes Types of segments:  Presents near neck.  Hermaphrodite, contain  At posterior part of parasite  Genital organs not single & sometimes 2 sets of except Pseudophyllidean differentiated. male and female genital parasites. systems (Dipylidium caninum)  All organs are atrophied except  Reproduction by uterus which is filled with eggs a. Self-fertilization and takes different shapes. (in single segment) or  Separated & passed to outside , b. Cross fertilization actively or passively with stool. (in different segments).  Consists of multiple testes throughout  On ventral surface of segments, consist of dorsal surface of segment, vasa bi- or trilobed ovary → Oviduct which efferentia, vas deference, seminal vesicle, unites with the common vitelline duct at ejaculatory duct, cirrus organ surrounded the ootype. by the cirrus sac, that opens in the common genital pore. Blind tube Opens to outside  In some cestodes only 3 testes are at ventral surface present in each mature segment e.g. through a separate Hymenolepis species. uterine pore  Common genital pore is present either on behind common Mid-ventral surface as genital pore Pseudophyllidean Packed mass Multiple vitelline Lateral borders as Cyclophyllidean like situated follicles scattered parasites. behind ovary in each segment 5 Cestodes 6  Cestodes The adult worms inhabit the small intestine of the definitive host. Cestode complete their life cycles in 2 different hosts, definitive and intermediate  Except Hymenolepis nana which may complete its life cycle only in man (definitive and intermediate hosts). Sometimes, man acts as an intermediate host and harbours the larvae of some cestodes in different organs and tissues, 1. Diphyllobothrium mansoni (sparganosis) 2. Taenia solium (cysticercosis) & Taenia multiceps (coenurosis) 3. Echinococcus granulosus (hydatid disease) 4. Hymenolepis nana.  The eggs are operculated and immature (diagnostic stage).  After maturation, in fresh water, the egg hatches liberating coracidium.  The coracidium is infective for the 1st intermediate host, ❶ Cyclops where it develops into 1st larval stage, procercoid.  When Cyclops is ingested by fish, the procercoid develops into the 2nd larval stage, plerocercoid (infective stage).  Man, and fish-eating animals, infected by ingestion of undercooked fish containing the infective stage.  The passed eggs are non-operculated, mature and containing hexacanth (6-hooked) embryos.  When the eggs are ingested by the intermediate host, the onchospheres are liberated, penetrate the intestinal wall, ❷ gain access to the circulation and develop into the larval stages in different organs and tissues.  Definitive host becomes infected by ingestion of these larval stages. 7 Cestodes 8 Cestodes 9  Cestodes Elongated Globular  Bothria Suckers and hooks Ventral Lateral  Open ventrally Blind  Scattered Single mass  Absent Present  Operculated Non-operculated Immature Mature Need water for Do not need water development Two hosts One host Solid larvae: Cystic larvae: 1. Procercoid 1. Cysticercus 2. Plerocercoid 2. Coenurus 3. Hydatid 4. Cysticercoid Diphyllobothrium latum Taenia saginata Diphyllobothrium mansoni Teania solium Diphyllobothrium Teania multiceps proliferum Echinococcus granulosus Echinococcus multilocularis Hymenolepis nana Hymenolepis diminuta Dipylidium caninum 10  Cestodes The pathogenicity of tapeworms is due to the adult worms and the larval stages. They cause pathogenic lesions by: 1) Competing with host nutrients as vitamin B12, e.g. D. latum. 2) Local intestinal inflammatory reactions, e.g. Hymenolepis nana. 3) Mechanical intestinal obstruction, e.g. Taenia saginata. 4) Migration to different organs and tissues with pressure effects, e.g. Diphyllobothrium mansoni (sparganosis), Taenia solium (cysticercosis) and Echinococcus granulosis (hydatid disease). The majority of tapeworm infections are asymptomatic. It may be symptomatic in heavy infection. Larval infections (extra-intestinal) are more serious. The clinical picture depends on the number, size and site of tissue larvae.  Diagnosed by :  Diagnosed by: Stool examination. Radio-imaging Tissue biopsy Immuno-diagnostic techniques. 11