Trematodes: Parasitic Flatworms (Quiz)

• Trematodes are multicellular helminthic parasites
• They have an egg, larva, and adult worm stages, observable microscopically and macroscopically

Reproduction

• Trematodes reproduce sexually via cross or auto fertilization

Shape

• Trematodes are dorsoventrally flat and unsegmented
• Schistosoma are leaf-like

Size

• Fasciolopsis buski is the largest trematode
• Fasciola hepatica is the largest liver trematode
• H. heterophyes and M. yokogawa are the smallest trematodes

Suckers

• Trematodes have 2 types of suckers
• Oral sucker for feeding
• Ventral sucker for attachment
• Acetabulum is present only in pseudophyllidian
• The word "trema" is Greek for "hole" and "eidos" means "appearance"
• Heterophyid has 3 types of suckers, the 3rd being genital suckers
• Trematodes have no hooks

Alimentary Canal

• Trematodes have an incomplete alimentary canal
• They have a blind ending gut with no anus
• They have intestinal cacae
• Waste is excreted via bilaterally symmetrical or midline bladders, and flame cells for filtration

Body Cavity

• Trematodes have no body cavity
• In nematodes, pseudocoelom exists instead of undifferentiated mesenchymal cells

Sexual Characteristics

• Trematodes are monoecious except for schistosomes
• They are hermaphroditic and not separate
• Males possess testes, vas deferens, and seminal vesicles
• Females possess ovaries, oviducts, vitelline glands, ootypes, and a uterus
• They have a complex reproductive system
• Schistosomes are diecious and only cross fertilize
• Monoecious trematodes auto fertilize and cross fertilize

Life Cycle

• Trematodes have 3 hosts, except for schistosomes, which have 2
• Intermediate host: snail
• Definitive host: man
• Some trematodes have 2 intermediate hosts, and 1 definitive host
• The first intermediate host is always a snail
• The second intermediate host can be a fish, crab, aquatic plant, snail, or ant
• Definitive host: man

Embryonic Development

• Trematodes are oviparous, laying eggs
• Some are viviparous releasing larva directly, or ovoviviparous

Schistosomes

• Dioecious, not hermaphroditic
• Schistosoma haematobium: bladder fluke
• Schistosoma mansoni: manson's fluke
• Schistosoma japonicum: oriental blood fluke
• Schistosoma mekongi
• Schistosoma intercalatum: diamond schistosome
• 6 S. malayensis

Faciola and Fasciolopsis

• F. hepatica: largest liver fluke, sheep/temperate liver fluke
• F. gigantica: giant liver fluke/ tropical (common in Ph)
• F. buski: largest trematode

Opisthorcis & Clonorchis

• Their testes are in tandem with ovary
• Circarae encyst in fish
• Opisthorchis felineus: cat liver fluke/Ciberia
• Opisthorchis viverrini: southeast asian liver fluke
• Clonorchis sinensis: chinese liver fluke/oriental

Heterophyes & Metagonimus

• Smallest trematodes (h)
• 3rd sucker (genital/gonotyl)
• Heterophyes heterophyes: vons siebolds
• Metagonimus yokogawai: yokogawa
• Paragonimus westermani: oriental lung fluke
• Lives in the lungs
• Testes are side by side, behind the ovary

Echinostoma & Artyfechinostomum

• E. ilocanum: garrison's fluke (PRISON first discovered)
• A. malayanum: malayan fluke
• Both have collar of spines near the oral sucker

Gastrodiscoides & Watsonius

• Possess a very large ventral sucker that is found in the posterior portion not in the midline/ventral side
• G. hominis: colon fluke (only in large intestine)
• W. watsoni: watson's fluke
• E. pancreatinum: pancreatic fluke Oral sucker is thick
• Dicrocoileum dendriticum
• Looks like a lancet
• Anterior and posterior end are tapered

Habitat

• Schistosomes are in the venous plexus, not literally in the blood cells
• Venous plexus means veins that are connected with each other
• Opisthorchis and Clonorchis are not really in the liver but in the bile duct which is just technically connected to the liver
• Heterophyes/Metagonimus spp. are found small intestine
• Opisthorchis spp. are found Bile duct
• Clonorchis spp. are found Bile duct

Egg Stage

• Their egg stage needs to be eaten first by the 1st IH (snail) before it can hatch its 1st stage larvae
• Heterophyes/Metagonimus spp.
• Opisthorchis spp.
• Clonorchis spp.
• MOT: ingestion
• Embryonated (if laid) "PEEF"
• Paragonimus spp.
• Echinostoma spp.
• Fasciola spp.
• Fasciolopsis spp. MOT: penetration

Larval Stage

• Miracidium
• Infective stage of the 1st IH except for (kato 3 gaina)
• Free living
• Ciliated
• Apical gland = releases proteolytic (lyse the protein in the skin) enzymes in the skin to the 1st IH to penetrate
• Sporocyst
• Remove its cilia, go to the liver and lymph spaces FOR SCHISTOSOMA ONLY UNDERGO ASEXUAL REP.
• Others: nothing happens in the sporocyst
• 1st and 2nd gen. In schistosomes
• Rediae
• Absent in schistosome
• Present in other trematodes
• 1st, 2nd asexual generation
• Circarae
• Infective stage of schistosomes
• Will move out of the snail and become free swimming again and infect the next IH
• The infective stage of the 2nd IH for all other trematodes EXCEPT for schistosomes spp.
• Schistosome spp. Circarae is the Infective stage to the DH (man) because it has no metacercarae
• For circarae stage, MOT are different:
• Plant = encystment
• Fish, crab, snail, ant = ingestion
• Once it is found in the 2nd IH, it will now develop to Metacercarae
• Metacercaria
• Infective stage of most trematode
• Infective to DH (man)
• Absent in schistosomes

Adult Worms

• Diecious species only Schistosoma spp.
• Monoecious species: e.g. Fasciola spp., Fasciolopsis spp.
• Clonorchis spp.

General Patterns

• First IH is always a snail
• Most species require a second IH.
• Hosts can be Fish, Crab,Plant or Ant
• Most clinically important species infect vertebrates

Blood Flukes - Schistosoma spp.

• The "most romantic parasite"
• Reside in the venous plexus
• "Schisto" split/divided, “soma" body
• Diecious, with male & female copulating (forever) for 20-30 yrs.
• Lacks a muscular pharynx. Sucker w/ delicate spine
• Cannot distinguish Schistosoma spp. by their adult stage, only by their EGG SATGE
• 2 hosts in lifecycle: snail (IH), man (DH)
• Tegument varies by species:
• S. japonicum: Smooth
• S. mansoni: Coarse tuberculate, large papillae w/ spines
• S. hematobium: Thick tuberculate, small tubercles

Schistosoma Species

• S. haematobium: Bladder Fluke, in the vesical venous plexus of the Urinary Bladder
• S. mansoni: Manson's Fluke, in the sigmoidorectal venous plexus
• S. japonicum: Oriental Blood Fluke, in the lleocecal venous plexus
• S. intercalatum: Diamond Schistosome, in the Mesenteric veins of the large intestine
• S. mekongi: resembles S. japonicum, in the Mesenteric veins of the small intestine

Egg Stage

• Non-operculated
• Possess spine-like projection
• Embryonated
• Schistosoma haematobium: Elliptical, sharp terminal spine, recovered in urine
• S. mansoni: Elliptical, sharp lateral spine, in stool
• S. japonicum: Rounded, small rudimentary knob, recovered in stool
• S. intercalatum: Related to S. Hematobium, equatorial diamond shape
• S. mekongi: Related to S. Japonicum, small inconspicuous knob Smaller than s. Japonicum

Larval Stage

• Miracidium develops into sporocyst and then cercaria
• Cercariae are the infective stage to the DH, forked tailed (bifurcated) elongated or forked (furcocercus cercarae)
• Rediae and Metacercariae is are absent in the larval stage of schistosoma
• MOT: Skin penetration

Other

• African schistosomes are more common in African countries such as S. mansoni, S. hematobium, and S. intercalatum
• Asian schistosomes are more common in Asian countries such as S. japonicum, S. mekongi, and S. malayensis
• IH (snails): species have different intermediate hosts
• Schistosoma japonicum – Oncomelania spp.
• Schistosoma mekongi – Neotricula aperta
• Schistosoma malayensis – Robertsiella spp.
• Schistosoma mansoni – Biomphalaria spp.
• Schistosoma haematobium – Bulinus spp.
• Schistosoma intercalatum – Bulinus spp.

Species Anatomy

• Female has no Laurer's canal, which are only in hermaphroditic worms
• Male is robust, thicker, with a gynecophoral canal for copulation
• Smaller anterior oral sucker compared to ventral sucker

S. haematobium

• Also known as vesical blood fluke or bladder fluke
• old parasite in Egyptian mummies, endemic in Egypt, Africa and West Asia
• Habitat: Vesical & Pelvic plexuses of veins
• Hosts: -Intermediate: Bulinus spp., Physopsis spp. -Definitive: Man

Simplified Life cycle

• Circarae penetrate skin of DH (man) in freshwater, loses fork tailed, becomes schistosomula
• Dermal veins in circulation --> heart (vena cava) --> lungs, will move out of the liver and mature into adults
• Adults go to the venous plexuses and uses their spines to penetrate the veins of the urinary bladder/ureter -Can cause hematuria and dysuria, releasing eggs in urine
• Embryonated eggs hatch in freshwater to release free swimming miracidium until it meets the IH (snail)
• Penetrates the snail, removes its cilia and becomes sporocyst
• Goes through 1st and 2nd asexual generation that mature into Circarae with fork tails
• Infect the DH

Diagnosis

Egg diagnostic stage. Occurs midday 12 noon - 3pm Must use unreserved urine

Detection Note:

• all schistosoma spp same ra ang life cycle ONLY differe sa organs na ila e infect/habitat Mature adult parasite copulate and goes to the the venus plexus, once adults mature, they migrate and copulate in the venous plexus. Immune recognition prevented by coating themselves with RBC antigens and major histocompatibility Ag

Pathogenesis

• Acure schistosomes is when reactions to the body occur once invaded by circarae.
• Symptoms include
• Dermatitis "Swimmers itch" causing maculopapular lesions due to release of toxic metabolite.
• Cough with non specific symptoms due to lung parasite

Disease

• Urinary bilharziasis or Egyptian hematuria or Urinary schistosomiasis
• Chronic Schistosomiasis occurs when a diseases goes untreated for an extended period of time.
• Is the result of deposited eggs and causes:
• Eggs in the bladder can cause dysuria and haematuria

Bladder will form egg granuloma , become inflamed and is surrounded by the Immune system

• Glandular metaplasia - change in epithelium due to egg clusters
• fibrotic changes and calcification will often develop and obstructive neuropathy that will block urine flow resulting in hydronephrosis

Late stage causes transitional cell carcinoma

1. Urine microscopy is performed on a 24 hr unpreserved urine

• Samples are examined embryonated, non-operculated,with terminal spine, pus, blood and quantification -Eggs may found in the seminal fluid and feces as well

2. Histology: Biopsy to examine the eggs
3. Ag detection - Detection of antigen in the serum /urine
4. Ab detection -IgE and IgG-4 cant differentiate between pat an present with allergic effects. It can only be used epidemiological study
5. Imaging- X-ray bladder to detect calcification

Treatment

1. Chemotherapeutic agents

   PraziQUANTEL 40-60mg/kg effective by targeting the tegument of of the schistosomes

2. METRIPHONATE 7.5mg/kg effective in paralyzing the worm. Note: it is important to improve sanitation in the community.

SCHISTOSOMA MANSONI

• Known as intestinal schistosomiasis or Manson's fluke -Profile of Africans as the consequence of the slave trade
• Widely distributed in Africa, South America & Caribbean Islands
• Habitat: Sigmoidorectal venous plexus (inferior mesenteric vein)
• Hosts: -Intermediate: Biomphalaria Australorbis and Tropicorbis spp.
• Definitive: Man, Monkeys & Baboons (endemic)

Explore the fascinating world of trematodes, multicellular helminthic parasites with complex life cycles. Learn about their unique characteristics, including sexual reproduction, dorsoventrally flattened shapes, and specialized suckers for feeding and attachment. This note covers their size variations and alimentary canal.