Platyhelminthes (flat worms) as parasites of medical interest

Platyhelminthes (flat worms) as parasites of medical interest

Type of parasites Protozoa Helminths Arthropods Nematodes Trematodes Cestodes Platyhelminthes

Platyhelminthes Trematoda Planaria Monogenea Digenea Cestoda

CESTODES (tape-worms)

General Characteristics

General Characteristics: Majority are long, segmented and tape-like are called tapeworms. Dorso-ventrally flattened. Size varies from a few mm to several meters. The life cycle of tapeworms is simple in the sense that there are few larval stages, but complicated in that at least one intermediate host is required as well as the definitive host. Adult worms are found in the intestinal canal of man and animals.

General Characteristics: There are 3 regions in an adult worm: Scolex (head) Neck Strobila (body or trunk) Consist of a series of segment called proglottids. Scolex has suckers and sometimes hooks that serve as organs of attachment. Once anchored to the host's intestinal wall, the tapeworm absorbs nutrients through its skin as the food being digested by the host flows past it, and it begins to grow a long tail.

General Characteristics: Sexes are not separate. Reproductive system is present and complete in each segment!!! Because each proglottid contains the male and female reproductive structures, they can reproduce independently. Body cavity is absent. Alimentary canal is entirely absent. Nervous system is present. Excretory system is present like some other flatworms, cestodes use flame cells (protonephridia), located in the proglottids, for excretion.

Tapeworms are exclusively hermaphrodites; they have both male and female reproductive systems in their bodies. The reproductive system includes one or many testes, cirrus, vas deferens and seminal vesicle as male organs, and a single lobed or unlobed ovary with the connecting oviduct and uterus as female organs. There is a common external opening for both male and female reproductive systems, known as genital pore, which is situated at the surface opening of the cup-shaped atrium.

Even though they are sexually hermaphroditic, self-fertilization is a rare phenomenon. In order to permit hybridization, crossfertilization between two individuals is often practiced for reproduction. During copulation, the cirrus of one individual connects with that of the other through the genital pore, and then exchange their spermatozoa. Uterus

General Characteristics According to maturity of reproductive organs, three types of segments of the strobila can be recognized: Immature: male and female organs are not differentiated; Mature: male and female organs have become differentiated (male organs appear first); Gravid: uteri are filled with eggs (other organs are atrophied or have disappeared). Gravid proglottids can be released from the tapeworm's posterior end and leave the host in feces. They drop off, carrying the tapeworm eggs to the next host. Older segments are pushed toward the tip of the tail as new segments are produced by the neckpiece.

Nervous system The main nerve centre of a cestode is a cerebral ganglion in its scolex. Motor and sensory innervation depends on the number and complexity of the scolex. Smaller nerves emanate from the ganglion to supply the general body muscular and sensory ending. The cirrus and vagina are innervated, and sensory endings around the genital pore are more plentiful than other areas. Sensory function includes both tactoreception (touch) and chemoreception (smell or taste).

Classification of Cestodes Infecting Man

Classification of Cestodes Infecting Man: Cyclophyllidean cestodes (a, b) Pseudophyllidean cestodes (c)

Classification of Cestodes Infecting Man: Pseudophyllidean cestodes Scolex (head) has two slit-like sucking grooves called bothria (1 on the dorsal surface and 1 on the ventral surface) instead of suckers.

Classification of Cestodes Infecting Man: Cyclophyllidean cestodes Scolex is quadrate with four cup-like round suckers called acetabula; An apical rostellum with hooklets may be present.

Order Pseudophyllidea characteristics: Large worms consisting of a long chain of segments. Vitellaria (vitellin glands) are widely scattered in the parenchyma and are composed of many acini. Genital pore is on the ventral surface of the segment and is not marginal. Uterus opens to the exterior through a uterine pore from which eggs come out.

Order Pseudophyllidea characteristics Eggs are operculated and can develop only in water. Eggs are immature when oviposited and oncosphere gives rise to ciliated embryo (coracidium). Larval development proceeds in two intermediate hosts: First larval stage is called procercoid Second larval stage is called plerocercoid (or spargano).

Order Cyclophyllidea characteristics Large or small worms consisting of chains of segments. Vitelline glands are concentrated in a single mass. Common genital pore is marginal (on lateral side of segment); No uterine opening for the exit of eggs from the gravid uterus. Eggs only escape from the rupture or disintegration of ripe segments.

Order Cyclophyllidea characteristics Eggs are not operculated and can develop only in the intermediate host, fully embryonated. Oncosphere is never a ciliated embryo; Larval development proceeds in one intermediate host: Cysticercus Hydatid cyst (or Coenurus) Cysticercoid

Main differences between Pseudophyllidean and Cyclophyllidean Cestodes Pseudophyllidean Cyclophyllidean Head or scolex uterus bears 2 slit-like grooves (bothria) no branching, convoluted uterine tubes assume the form of rosettes Uterine pore present absent bears 4 cup-like suckers (acetabula) branching may or may not be present Common genital pore eggs Ventral; in the midline Operculated; gives rise to ciliated larvae lateral Not operculated; do not give rise to ciliated larvae

Pseudophyllidean cestodes infecting man: Adult worms in Intestine Diphyllobothrium latum (Fish Tapeworm) Larval stages in Man Spirometra mansoni (spargano)

Cyclophyllidean cestodes infecting man: Adult Worms in the Intestine Taenia saginata Taenia solium Hymenolepis nana Hymenolepis diminuta Dipylidium caninum Larval Stages in Man Echinococcus granulosus and E. multilocularis (Hydatid cyst) Taenia solium (Cysticercus)

Pseudophyllidea: Diphyllobothrium latum

Diphyllobothrium latum Common Name: Fish Tapeworm Broad Tapeworm Morphology Adult worm is yellowish grey in colour. Dark central markings in the strobila are due to the egg-filled uterus. Measures 3 to 10 meters in length! Life-span is for a period of 5 to 15 years.

Diphyllobothrium latum

Diphyllobothrium latum Scolex is spoon-shaped or spatulate. Scolex bears 2 slit-like grooves called bothria (1 on the dorsal surface and 1 on the ventral surface). Scolex has no rostellum and no hooklets. Neck is thin and unsegmented and is much longer than the head.

Diphyllobothrium latum 3,000 to 4,000 proglottids; A mature segment is filled with male and female reproductive organs. In gravid proglottids uterus at the center of the segment appears in the form of a rosette. Terminal segments shrink and becomes empty as eggs are constantly discharged. Dried up segments break off from the body in chains and are passed out in the host s feces.

Diphyllobothrium latum

Diphyllobothrium latum Ova Passed out in the host s feces in large numbers. Contains abundant granules and unsegmented ovum. Inconspicuous operculum at one end and a small knob at the other end. Does not float in saturated solutions of common salt. A single egg gives rise to a single larva. Not infective to man. Egg

Diphyllobothrium latum larva Passed first in water and then in the respective intermediate hosts. 3 stages: First larval stage Coracidium Ciliated oncosphere that develops from egg in water Second larval stage Procercoid Spindle-like solid body with cephalic invagination Found inside the cyclops (the first intermediate host) Third larval stage Plerocercoid Head is invaginated in the neck Found in the fresh water fish (the second intermediate host)

Diphyllobothrium latum Final Host Man, dog, cat (small intestine) 1 st I.H. Cyclops or Diaptomus 2 nd I.H. Fresh water fish, pike, trout, salmon, perch Mode of Infection for humans Ingestion of imperfectly cooked infected fish or roe containing plerocercoid larvae Infection Diphyllobothriasis G.I. disturbances and anemia Diagnosis Microscopic examination of feces for the characteristic operculated eggs

Spirometra spp.

Sparganosis

Cyclophyllidea: Taenia spp.

Taenia spp. life cycle

Taenia saginata

Beef Tapeworm; Unarmed Tapeworm of Man; Scolex is globular in outline with 4 circular suckers; Adult worms are white and semi-transparent; Measures about 5-10 meters or sometimes up to 24 meters!!! 1000 to 2000 proglottids; Live up to 10 years or more. Taenia saginata

Common genital pore is marginally situated; Vagina is provided with a sphincter muscle; Gravid proglottid consists of a uterus and a central longitudinal stem with 15-30 branches on each side; Gravid proglottid contains 97000 to 124000 ova; Gravid segments are expelled singly and force their way through the anal sphincter; Free gravid proglottid crawls out of the anal orifice and oviposits on the perianal skin. Taenia saginata

Taenia saginata Ova Liberated by rupture of ripe proglottids; No uterine opening; Spherical, thin, outer transparent shell; Inner embryophore is brown, thick walled and radially striated; Has an oncosphere with 3 pairs of hooklets; Eggs are resistant and remain viable for 8 weeks; Infective only to cattle.

Taenia saginata Final Host: Man Intermediate Host: cattle, cow buffalo Mode of Infection: eating beef containing cysticercus Pathogenesis (Taeniasis): Passage of proglottids in stool Mild irritation at site of attachment Epigastric pain Hunger fangs Weakness Weight loss Loss of appetite Pruritis Obstruction in intestine but also in bile and pancreatic ducts and appendix because proglottids are actively motile!

Taenia saginata Diagnosis Identifying characteristic eggs, proglottids or scolex Usual specimen is gravid proglottids (lateral branches 15-20) Concentration techniques for eggs (eggs rarely passed out in stool) Perianal swabs Treatment Praziquantel 5-10mg/kg single dose Criteria for cure Recovery of the scolex Negative stool examination 3 months after treatment

Taenia solium

Taenia solium Pork tapeworm; Armed tapeworm of man; Scolex is globular in outline with 4 circular suckers; Scolex has a rostellum armed with a double row of alternating large and small hooklets; Rostellar hooklets are shaped like daggers or Arabian poniards. 800-900 proglottids; Adult worms measure 2-5 meters and live up to 25 years!

Common genital pore is marginal and thick lipped; Vaginal opening is not guarded by a muscular sphincter; Gravid segments are expelled passively in chains of 5-6 at a time and not singly; Gravid proglottids contains approx. 30.000 to 50.000 eggs. Taenia solium

Taenia solium Ova Same as those of T. saginata; Infective to man as well as pigs; Thick brown striated embryophore surrounding a hexacanth embryo. oncosphere hooks

Taenia solium Final Host: Man Intermediate Host: Pig (accidentally Man, cysticercosis) Mode of infection: eating measly pork containing cysticercus Diagnosis: stool examination for proglottids/eggs

Taenia solium Pathogenesis Mild, non-specific abdominal complaints Proglottids are not as motile as T. saginata so organ obstruction is less likely. Cysticercosis Multiple Develop in any organ or tissue Neurocysticercosis (most serious zoonotic disease) Chorioretinitis vasculitis

Cysticercosis

Taenia solium Diagnosis: Intestinal Identifying the characteristic proglottids, eggs or scolex Cysticercosis Computed Axial Tomography Magnetic Resonance Imaging Treatment Praziquantel: 5-10 mg/kg single dose for children and adults Niclosamide not available locally Criteria for cure: Recovery of scolex Negative stool exam 3 months after treatment

Comparison between T. saginata and T. solium Taenia saginata Taenia solium length 5-10 meters 2-5 meters Head or scolex Large, quadrate, no rostellum and hooks Armed; with rostellum; with hooklets Number of proglottids 1000 to 2000 Below 1000 Expulsion Expelled singly and may be forced through the anal sphincter uterus Highly branched with 15-30 lateral branches on each side; thin; dichotomous Expelled passively in chains of 5 or 6 Lateral branches 5-10 on each side, thin, dendritic and vaginal sphincter is absent testes 300-400 follicles 150-200 follicles

Cyclophyllidea: Echinococcus granulosus

Echinococcus granulosus Taenia echinococcus Dog Tapeworm Hydatid Worm Man harbours the larval form and not the adult worms which however is found in the intestine of dogs and canines

Echinococcus granulosus Adult worms are small (3-6 mm in length) It is composed of a Scolex Neck Strobila 3 segments (occassionally 4) Immature Mature Gravid

Echinococcus granulosus Scolex bears 4 suckers and a protrusible rostellum with 2 circular rows of hooks.

Echinococcus granulosus

Echinococcus granulosus

Echinococcus granulosus Ova Ovoid in shape Resemble Taenia ova Hexacanth embryo with 3 pairs of hooks Infective to: Man Cattle Sheep and other herbivorous animals

Echinococcus granulosus Larva Found within the hydatid cyst developing inside the intermediate host; Represents the structure of the scolex of the future adult worm; Young larva are transformed into a hollow bladder (hydatis, drop of water); Brood capsules develop within the cysts and may contain thousands of scolices; On entering the final host, the scolex armed with a rostellum and 4 suckers become adult worms.

Echinococcus granulosus Definitive Host Dog Wolf Fox Jackal Intermediate Host Sheep Pig Cattle Horse Goat

Echinococcus granulosus

Echinococcus granulosus Pathogenesis Echinococcosis Pathology is caused by the developing larval cyst in the intermediate host; Most common site of involvement is the liver; Echinococcus granulosus cyst: Unilocular hydatid cyst Echinococcus multilocularis cyst: alveolar cyst Some may be asymptomatic for years; Rupture of cyst in the lungs may present coughing accompanied by allergic reactions.

Echinococcus granulosus

Echinococcus granulosus Encysted scolices of Echinococcus granulosus in lung "hydatid sand"

Echinococcus granulosus Encysted scolices of E. granulosus in lung "hydatid sand"

Echinococcus granulosus Encysted scolices of E. granulosus in lung "hydatid sand"

Echinococcus granulosus Diagnosis Radiographic findings Immunodiagnosis Antibody detection IHA IFA EIA Antigen detection

Echinococcus granulosus Treatment Surgical resection: not 100% effective Scolicidal agent Hibitane 95% ethanol Hypertonic 30% Normal Saline Solution PAIR technique for inoperable cyst Puncture, Aspiration, Injection, Reaspiration Intervention Albendazole

Hymenolepis species

Hymenolepis sp. Genus is derived from the membranous character of the egg shell hymen ; 3 testes in each mature segment; Uterus is sac-like and transverse; Eggs possess two membranes (outer membrane is thin and transparent); Larval stage is called cysticercoid; Small bladder containing the invaginated head proximally and a solid, elongated portion as a caudal appendage; There are 2 species: Hymenolepis nana Hymenolepis diminuta

Cyclophyllidea: Hymenolepis nana

Hymenolepis nana Dwarf Tapeworm Smallest tapeworm infecting man Found worldwide Mainly among children Only human tapeworm that can complete its life cycle in a single host Man can harbour both the adult and larval stages of the parasite Exception to the general rule that: Helminthes do not multiply inside the body of the definitive host

Hymenolepis nana Adult found in the ileum Delicate strobila 25 mm to 45 mm Worms may be present in large numbers from 1,000 to 8,000 Short life span, about 2 weeks Up to 200 proglottids Transverse uterus 3 testes

Hymenolepis nana Scolex Subglobular 4 suckers Provided with a short retractile rostellum armed with a single row of 20-30 hooklets Rostellar hooklets are shaped like tuning forks

Hymenolepis nana Ova Spherical or oval Floats in saturated solutions of common salt 2 distinct membranes Outer membrane is thin transparent and colourless Inner embryophore that encloses an oncosphere with 3 pairs of lancet shaped hooklets Intermembranous space is filled with yolk granules and 4-8 polar filaments emanating from little knobs at either end of the embryophore

Hymenolepis nana Mode of transmission: Direct Host ingests eggs that hatches in the duodenum Indirect pathway Accidental ingestion of infected arthropod intermediate host like rice and flour beetles in which cysticercoid larvae are released and develop into adult worms in the small intestine of the host

Hymenolepis nana

Hymenolepis nana Pathogenesis Symptoms are produced due to patient s immunological response to the parasite Asymptomatic for light worm burden Headache Dizziness (vertigo) Anorexia Pruritus of the anus Abdominal pain Pallor Desquamation of intestinal epithelial cell or as serious as necrosis may occur Regulatory immunity will eventually limit the infection

Hymenolepis nana Diagnosis Demonstration of characteristic ova in the stool Proglottids are not recovered because they undergo degeneration prior to passage Treatment Praziquantel 25mg/kg single dose Drug dosage is higher than that of taeniasis because of resistant cysticercoids in intestinal tissue

Hymenolepis nana Epidemiology Countries with warm temperature Southern USA Latin America Mediterranean East Asia Philippines

Cyclophyllidea: Hymenolepis diminuta

Hymenolepis diminuta Rat tapeworm Common parasite of rats and mice Accidental human infections Differs from Hymenolepis nana in morphology and life cycle because it requires an intermediate host 2 Hosts Larval stage: cysticercoid is passed in fleas Adult stage: in rats and mice and accidentally in humans especially children who accidentally ingest infected fleas

Hymenolepis diminuta

Hymenolepis diminuta Adult Larger than Hymenolepis nana Measures 60 cm in length

Hymenolepis diminuta Scolex Unarmed rostellum 4 suckers

Hymenolepis diminuta

Hymenolepis diminuta Proglottid (800 1000) Mature proglottids of H. diminuta from the laboratory rat. The three spherical bodies are testes which surround the ovaries, ootype and vitelline glands. The genital pores are on the left margin

Hymenolepis diminuta Ova Larger than H. nana Outer shell is yellowish in color Inner embryohore has 2 knob-like thickenings No polar filaments

Hymenolepis diminuta Cysticercoid of H. diminuta The suffix indicates it is like a cysticercus but this larva has no bladder but instead has a tail. The dark body within the spherical portion is the scolex. The longer the tail, the more mature the cysticercoid. This stage is found inside the intermediate host.

Hymenolepis diminuta Pathogenesis Hymenolepiasis Worm burden in rodents is relatively low In man, clinical manifestations are minimal and non-specific

Hymenolepis diminuta Treatment Praziquantel 25 mg/kg body weight single dose Epidemiology World wide Common among children due to ingestion of infected grain beetles, dried fruits, flour and cereals Prevalence of H. diminuta in Philippine rats is about 8%.

Cyclophyllidea: Dipylidium caninum

Dipylidium caninum Double Pored Dog Tapeworm Presence of bilateral genital pores in each segment Common intestinal parasite of dogs

Dipylidium caninum Adult 10-70 cm in length Pale reddish

Dipylidium caninum Scolex Small and globular 4 deeply cupped elliptical suckers Protrusible/retractile rostellum Rostellum has 1-7 rows of rose thorn shaped hooklets

Dipylidium caninum Strobila 200 proglottids narrow

Dipylidium caninum Mature proglottids 2 sets of male and female reproductive organs Bilateral genital pores

Dipylidium caninum Gravid proglottids A. Have size and shape of pumpkin seeds A B. Filled with capsules or packets of 8-15 eggs enclosed n an embryonic membrane B

Dipylidium caninum Proglottids

Dipylidium caninum

Dipylidium caninum

Dipylidium caninum Ova Passed out in the feces along with the proglottids Released by contraction of proglottids or disintegration outside the host Spherical Thin shelled With a hexacanth embryo These eggs, still wrapped in fragile egg packets, came from a single motile and gravid proglottid

Dipylidium caninum Intermediate hosts: Dog flea (Ctenocephalides canis, Trichoedectes canis) Cat flea (Ctenocephalides felis) Human flea (Pulex irritans)

Dipylidium caninum Pathogenesis Dipylidiasis Rarely multiple Symptoms are minimal Slight intestinal discomfort Epigastric pain Diarrhea Anal pruritus Allergic reactions

Dipylidium caninum Treatment Praziquantel 5-10 mg/kg body weight single dose Epidemiology USA Rhodesia Argentina China Philippines