MLS Review - Parasitology - Cestodes

MEDICAL LABORATORY SCIENCE REVIEW • CLINICAL PARASITOLOGY: CESTODES OUTLINE • Cestodes o General Characteristics o Laboratory Diagnosis o Classification based on Habitat o General Parts o D. latum o T. solium vs. T. saginata o H. diminuta o H. nana o D. caninum o E. granulosus • CLASSIFICATION BASED ON HABITAT • • CESTODES GENERAL CHARACTERISTICS • • • • • • • • • Flat and ribbon like bodies, have segmented bodies Elongated and can reach up to meters It does not have body cavity or alimentary tract It has excretory, nervous and reproductive system o One segment may contain both male and female reproductive organs Forms: Adult, one or more larva and ova o Ova → Larva → Adult o Procercoid - 1st stage larva o Plerocercoid - 2nd stage larva; infective to man All have hexacanth embryo except: Echinococcus granulosus o Hexacanth embryo - with six hooks o E. granulosus - contains hydatid cyst All are heteroxenous, except: Hymenolepis nana o Heteroxenous - infesting more than one kind of host All are under Cyclophyllidea, except: Diphyllobothrium latum (Pseudophyllidea) Adult consist of three parts: o Head (Scolex) - anterior part ▪ Organ/region of attachment/adapted ▪ Contains rostellum, hooklets, suckers o Neck - contain germinal tissues (site of origin of reproductive organs) ▪ Region of growth for segments (proglottids) ▪ Considered as the budding zone o Trunk (Strobilla) - entire body containing segments ▪ Immature proglottids - near the neck; only contains tissues ▪ Mature proglottids - mid part, contains reproductive organs ▪ Gravid/Ripe Proglottids - after mid part; composed of eggs • End portion detaches and goes with feces LABORATORY DIAGNOSIS • • Stool – most commonly used to identify tapeworms o eggs, occasional gravid proglottid and rare scolex after treatment Biopsy – for Echinococcus granulosus Serological Test - ELISA o Principle: ag-ab reaction between parasite ag and human ab Perianal Swab – High recovery for E. vermicularis ova Adult Worm in Intestines (Definitive Host) (usually found in small intestine) o D. latum o T. solium o T. saginata o H. nana o H. diminuta Larval Stage in Man (Accidental Intermediate Host) o D. latum (sparganosis) o T. solium o Echinococcus granulosus GENERAL PARTS HEAD (SCOLEX) • • • • • • • • • • Four cup shaped structure (suckers) – for attachment in the intestinal mucosa o Cyclophyllidea - cuboidal shape o Pseudophyllidea - spatula shape o Bothria - absence of suckers Rostellum – fleshy hooks or apical protrusion o Some may contain hooklets Treatments are based on removing the scolex in the intestinal mucosa T. solium – globular scolex with hooklets H. nana – globular scolex, retractile rostellum Y shape D. caninum – prominent conical rostellum with protrusion E. granulosus - globular scolex with hooklets D. latum – almond/spatulate/spoon-shaped scolex T. saginata - globular scolex without hooklets; short rostellum H. diminuta – globular scolex without hooklets; rudimentary (undeveloped) apical rostellum NECK • • Region of growth for strobila Budding zone where segments originates TRUNK (STROBILA) • • • • Entire chain of proglottids or segments Young/Immature, Mature, Gravid Mature Segment - Hermaphroditic segments Ripe/Gravid segment - Uterus filled eggs Mature Gravid Diphylobothrium NO DISTINCT Broader than long latum Taenia solium 100-200 follicular Longer than broad (pork tapeworm) testes Taenia saginata 300-400 follicular Longer than broad (beef tapeworm) testes Hymenolepis nana 3 testes and 1 Saccular Uterus and diminuta ovary Echinocccus 1 set of Coiled/Loosely twisted granulosus reproductive uterus with midline structure lateral evagination • E. granulosus - contains head, neck, and 1 each immature, mature, and gravid segments 1 Diphylobothrium latum • • • • • • • Also known as Broad Fish Tapeworm or Russian Broad Tapeworm Only pseudophyllidean cestode to infect man; May cause vitamin B12 deficiency (Megaloblastic Anemia) Scolex: With 2 false cuplike suckers or sucking grooves (bothria); Almond shape or spatulate or spoon-shaped head Proglottid: Wider than they are long; Rosette gravid proglottid (central uterine); ovary Ova o Size range: 55-75 µm long, 40-55 µm wide o Shape: Somewhat oblong o Embryo: Undeveloped, termed coracidium o Shell: Smooth; yellow-brown in color o Other features: Operculum on one end; terminal knob on opposite end Life Cycle of Diphylobothrium latum o Definitive Host: man o Intermediate Host: fresh water crustaceans ▪ 1st IH: Copepods/cyclops ▪ 2nd IH: Fresh water fishes like pile, eel, trout (2nd IH is usually a smaller fish that is ingested by a larger fish) o Infective Stage To: ▪ Man: plerocercoid ▪ 2nd IH: procercoid (1st stage larva) ▪ 1st IH: procercoid Taenia solium vs Taenia saginata Common Name Definitive Host Intermediate Host Infective Stage Length Scolex Proglottid or Segment Uterus (Lateral Branches) Stain: India ink Vaginal Sphincter T. solium Armed Tapeworm (possess scolex with rostellum & hooklets); Pork tapeworm Man; prok; Cysticercus cellulosae; egg 2-3m Small and globular Rostellum with hooks (Double Crown) <1000 T. saginata Unarmed Tapeworm; Beef tapeworm Accessory Ovarian Lobe Ova Note: hexacanth embryo • T. solium Mature segment T. saginata Absent • Size range: 28-40 µm by 18-30 µm • Hooklets: Three pairs; hexacanth embryo • Other features: Radial striations on yellow: brown embryophore Apolysis - natural detachment of gravid proglottid from the main body Hymenolepis diminuta • • • • • Also known as Rat Tapeworm Infective stage to man in H. diminuta – Cysticercoid larva Scolex: With four suckers; small (rudimentary) apical rostellum without hooks (underdeveloped) Proglottid: Rectangular; Saclike uterus filled with eggs; Often difficult to see Ova o With hexacanth embryo o Average size: 55 by 85 µm o Hooklets: Three pairs; hexacanth embryo o Polar thickenings: Present o Polar filaments: Absent o Embryophore: Present; colorless Man; cattle/cow; Cysticercus bovis 5-10m Large globular Without rostellum nor hooks 1,000-2000 Square; 7-15 thick & Rectangular; 15-30 dendritic on each side thin and dichotomous on each side Absent Present 2 Hymenolepis nana • • • • • • Also known as Dwarf Tapeworm Smallest cestode to infect human intestine; Most common cestode in humans Deadliest due to its small size’s ability to migrate to brain Scolex: With four suckers; small rostellum with one row of hooks Proglottid: Rectangular; Saclike uterus filled with eggs Ova: o Average size: 45 by 38 µm o Hooklets: Three pairs; hexacanth embryo o Polar thickenings: Present o Polar filaments: Present o Embryophore: Present; colorless • • • • • • Adult: scolex, small neck, and three proglottids, one at each developmental stage (immature, mature, gravid) o With twisted or coiled uterus Ova: indistinguishable to Taenia eggs; cannot be recovered in human Hydatid Cyst Fluid – highly antigen that may lead to anaphylactic shock Casoni Test – Skin Test for E. granulosus Infective stage of man to E. granulosus: hydatid cyst Adult: Dipylidium caninum • • • • • Also known as Dog or Cat Tapeworm or Pumpkin Seed Tapeworm or Double Pored Tapeworm Infective Stage to Dipylidium caninum – Cysticercoid larva Scolex: With four suckers; club shaped armed rostellum with up to seven circlets Proglottid: Pumpkin Seed mature and gravid proglottid; Two sets of reproductive organs; o With two genital pores; full eggs enclosed in embryonic membrane o Proglottids contain pumpkin-seed like amount o Vase-shaped segments Ova o Number of eggs in enclosed packet: 5-30 o Diameter range per egg: 30-60 µm o Individual egg features: Six-hooked oncosphere Echinococcus granulosus • • • Also known as Dog Tapeworm or Hydatid Tapeworm Definitive Host: Dogs Intermediate Host: Sheep and Man o Man is accidental host 3