أسئلة الثالثة بارا PPPM (قبل التعديل)

• Cestoda are long, segmented, tape-like worms.
• They are endoparasitic, and adults inhabit the small intestine of a definitive host.
• Some cestodes invade human tissue during their larval stages, forming tissue tapeworms.

Classification

• Order Pseudophyllidea includes:
  • Diphyllobothrium mansoni (Spirometra mansoni)
  • Diphyllobothrium latum
  • Diphyllobothrium proliferum
• Order Cyclophyllidea includes:
  • T. solium
  • Taenia saginata
  • T. multiceps
  • Echinococcus granulosus
  • E. multilocularis
  • Hymenolepis nana
  • Dipylidium caninum
  • H. diminuta

Mode of Infection

• Humans can be infected by adult tapeworms or larval stages.

Intestinal Cestodes Infections

• Human infection occurs in the definitive host with adult cestodes.
• These includes:
  • Taenia saginata
  • Taenia solium
  • Hymenolepis nana
  • Hymenolepis diminuta
  • Diphyllobothrium latum
  • Dipylidium caninum

Extra-Intestinal or Tissue Cestodes

• Human infection occurs in the intermediate host with larval cestodes
• These include:
  • Cysticercus cellulosa of Taenia solium (Cysticercosis)
  • Coenurus cyst of Multiceps multiceps (Coenurosis)
  • Sparganum or plerocercoid larva of Diphyllobothrium mansoni or D. proliferum (Sparganosis)
  • Hydatid cyst of Echinococcus granulosus or E. multilocularis (Hydatid disease)
  • Cysticercoid larva of Hymenolepis nana

General characteristics

• Cestodes are flattened dorso-ventrally and vary in length from a few millimeters to several meters.
• They lack a body cavity and a digestive system.
• Nutrition occurs via absorption of nutritive materials from the surrounding medium through the body wall.
• The excretory system includes multiple flame cells, collecting tubules, and 4 longitudinal excretory ducts (2 dorsal and 2 ventral) that run laterally and open into a bladder in the last segment.
• They have a nervous system with multiple central nerve ganglia in the scolex region.
• The tegument absorbs nutrients through the body wall.
  • It has a protective function.
  • It secretes chemicals to prevent worm digestion.

Morphology

• Adult worms are divided into three parts: scolex, neck, and strobila
• The scolex has variable shapes and organs of attachment such as bothria or suckers to hold the tapeworm in place.
• There are two main types of holdfast organs:
  • Suckers are typically 4 cup-shaped muscular suckers, or 4 cup-shaped muscular suckers with a rostellum armed with rings of hooks.
  • Bothria are two elongated shallow grooves or pits.
• The neck is the region of growth.
• The strobila consists of segments classified according to the degree of maturity of their genital organs: immature, mature, and gravid segments.

Types of Segments

Immature Segment

• Located near the neck.
• Genital organs are not yet differentiated.

Mature Segment

• They are Hermaphroditic, having single or paired male and female genital systems, such as in Dipylidium caninum.
• Reproduction can occur through self-fertilization (within a single segment) or cross-fertilization (between different segments).

Gravid Segment

• Contains:
  • a posterior part of the parasite, except in Pseudophyllidean parasites.
  • atrophied organs except for the uterus, which is filled with eggs and varies in shape.
• Gravid segments are either separated and passed with stool actively or passively.

Male Genital System

• Consists of multiple testes throughout the dorsal surface of the segment.
• Consists of :
  • vasa efferentia
  • vas deferens
  • seminal vesicle
  • ejaculatory duct
  • cirrus organ surrounded by the cirrus sac that opens in the common genital pore.
• Some cestodes, like Hymenolepis species, have only 3 testes in each mature segment.
• The common genital pore is present on the mid-ventral surface in Pseudophyllidean parasites or on the lateral borders in Cyclophyllidean parasites.

Female Genital System

• Located on the ventral surface of segments.
• It consists of a bi- or trilobed ovary that connects to the oviduct and unites with the common vitelline duct at the ootype.
• Cyclophyllidea have a blind tube uterus.
• Pseudophyllidea uterine opens to the outside at ventral surface.
• Cyclophyllidea: Packed mass-like situated behind the ovary.
• Pseudophyllidea contain multiple vitelline follicles scattered in each segment.

Life cycle

• The life cycle is completed in 2 different hosts, definitive and intermediate
• Adult tapeworms live the small intestine of definitive hosts.
• Cestodes need two hosts (definitive and intermediate) to complete their life cycles.
• An exception is Hymenolepis nana, which can complete its life cycle in only one host.
• Sometimes, humans can act as an intermediate host and harbor cestode larvae in different organs.

Diphyllobothrium mansoni (Sparganosis)

• Taenia solium (cysticercosis) or Taenia multiceps (coenurosis)
• Echinococcus granulosus (hydatid disease)
• Hymenolepis nana
• Pseudophyllidean tapeworms have operculated, immature eggs (diagnostic stage).
• After maturation, eggs hatch releasing coracidium needing fresh water.
• The coracidium is infective for the first intermediate host Cyclops where it changes to procercoid.
• When Cyclops is ingested by fish, the procercoid develops into the plerocercoid (infective stage)..
• Humans and fish-eating animals are infected when they eat undercooked fish with plerocercoid.
• Cyclophyllidean tapeworms have non-operculated, mature eggs with hexacanth (6-hooked) embryos.
• When the eggs are ingested by the intermediate host, onchospheres are freed, penetrate the intestinal wall, enter the circulation, and develop into larval stages.
• Definitive hosts become infected upon ingestion of the larval stages in different organs and tissues.

Differences Between Pseudophyllidea and Cyclophyllidea

Scolex

• Pseudophyllidea: Elongated and has Bothria
• Cyclophyllidea: Globular and has suckers and hooks

Mature Segment

• Genital pore:
  • Pseudophyllidea: Ventral and open ventrally
• Cyclophyllidea: Lateral and Blind
• The uterus
  • Pseudophyllidea: Scattered
  • Cyclophyllidea: Single mass
• The vitellaria
  • Pseudophyllidea: Absent
  • Cyclophyllidea: Present
• Gravid Segment:
  • Pseudophyllidea: Operculated
  • Cyclophyllidea: Non-operculated

Eggs

• Pseudophyllidea: Immature and needs water for development.
• Cyclophyllidea: Mature and don't need water.

Intermediate Hosts

• Pseudopphyllidea has Two hosts
• Cyclopphyllidea has One host

Larval Stages

• Pseudophyllidea has solid larvae: Procercoid and Plerocercoid
• Cyclophyllidea has Cystic larvae: Cysticercus, Coenurus, Hydatid, and Cysticercoid

Members

• Pseudophyllidea: Diphyllobothrium latum, Diphyllobothrium mansoni, Diphyllobothrium proliferum.
• Cyclophyllidea: Taenia saginata, Taenia solium, Teania multiceps, Echinococcus granulosus, Echinococcus multilocularis, Hymenolepis nana, Hymenolepis diminuta, Dipylidium caninum.

Pathogenicity

• The pathogenicity in tapeworms comes from adults and larvae.
• Pathogenic lesions are caused:
  • Competing with the host for nutrients such as vitamin B12 (e.g., D. latum).
  • Local intestinal inflammatory reactions (e.g., Hymenolepis nana).
  • Mechanical intestinal obstruction (e.g., Taenia saginata).
  • Migration to different organs and tissues with pressure effects (e.g., Diphyllobothrium mansoni (sparganosis), Taenia solium (cysticercosis), and Echinococcus granulosus (hydatid disease)).

Clinical Picture

• Most tapeworm infections are asymptomatic
• Heavy infections may cause symptoms.
• Larval infections (extra-intestinal) are more serious.
• Clinical presentation depends on the number, size, and location of tissue larvae.

Diagnosis

• Diagnosis of intestinal tapeworm infections is by stool examination
• Diagnosis of extra-intestinal infections is by:
  • Radio-imaging
  • Tissue biopsy
  • Immuno-diagnostic techniques.