Trematodes (Flukes)

Trematodes (Flukes)

• Unsegmented helminths that are flat and broad
• Resemble tree leaves or flatfish
• Name "Fluke" originates from the Anglo-Saxon word 'floc', meaning 'flatfish'
• Characterized by prominent suckers with a central hole (trema: hole, eidos: appearance in Greek)

Classification

• Systemic: Based on evolutionary relationships (see Table 13.1 for details)
• Habitat: Categorized by the location in the host body (see Table 13.2)
• Blood flukes infect the blood
• Liver flukes infect the liver
• Intestinal flukes infect the intestines
• Lung flukes infect the lungs

Zoological Classification (Table 13.1)

• Schistosomatoidea superfamily includes the Schistosomatidae family
• Schistosoma genus includes species like S. haematobium, S. mansoni, S. japonicum, S. mekongi, and S. intercalatum
• Paramphistomatoidea superfamily contains the Zygocotylidae family
• Gastrodiscoides Watsonius genus includes the species G. hominis, W. watsoni
• Echinostomatoidea superfamily contains the Fasciolidae family
• Fasciola Fasciolopsis genus includes the species F. hepatica, F. buski
• Opisthorchioidea superfamily includes Opisthorchiidae and Heterophyidae families
• Opisthorchis genus includes species like O. felineus and O. viverrini
• Clonorchis Heterophyes and Metagonimus genera include the species C. sinensis, H. heterophyes and M. yokogawai
• Plagiorchioidea superfamily contains the Paragonimidae family
• Paragonimus genus includes the species P. westermani

Habitat Classification (Table 13.2)

• Blood flukes include Schistosoma haematobium, Schistosoma mansoni, and Schistosoma japonicum
• Liver flukes include Clonorchis sinensis, Fasciola hepatica, and Opisthorchis spp
• Intestinal Flukes include Fasciolopsis buski, Heterophyes heterophyes, Metagonimus yokogawai, and Watsonius watsoni
• Large intestine: Gastrodiscoides hominis
• Lung flukes include Paragonimus westermani

General Characteristics of Flukes

• Size varies from barely visible (Heterophyes) to large and fleshy (Fasciola and Fasciolopsis)
• Possess 2 muscular cup-shaped suckers (distomata):
  • Oral sucker surrounds the mouth at the anterior
  • Ventral sucker (acetabulum) is located in the middle, ventrally
• Body covered by an integument which may have spines, papillae, or tubercles
• Lack a body cavity, circulatory, and respiratory systems
• Alimentary system includes an oral sucker-surrounded mouth, a muscular pharynx, and an esophagus
• Esophagus bifurcates anterior to the acetabulum, forming 2 blind caeca that reunite in some species, appearing like an inverted Y
• Anus is absent
• Excretory system includes flame cells and collecting tubules that empty into a posterior median bladder
• Rudimentary nervous system made of paired ganglion cells
• Most are hermaphroditic (monoecious) except schistosomes, which have separate sexes (dioecious)
• Hermaphroditic flukes self-fertilize, although cross-fertilization can occur
• Schistosomes have sexes separate, with males and females living in copula, the female residing in the male's gynecophoric canal
• Trematodes are oviparous, laying operculated eggs, except in schistosomes

Life Cycle of Flukes

• Medically significant trematodes belong to Digenea subclass, digenetic, requiring 2 hosts
• Definitive hosts
  • Mammals
  • Humans
  • Animals pass the adult stage of the parasite
• Intermediate hosts
  • Freshwater mollusks
  • Snails, where asexual/larval stages occur
• Some require a second intermediate host
  • Fish
  • Crabs for encystment
• Eggs from the definitive host hatch in water, producing the motile, ciliated miracidium
• Miracidium infects the snail intermediate host
• Miracidium develops into a sporocyst ('bladder containing seeds'), where germ balls proliferate for asexual replication
• In Schistosomes sporocyst develops into a second-generation sporocyst, forming cercariae via sexual multiplication
• In hermaphroditic trematodes sporocyst matures into redia
• Redia produces cercariae
• Cercariae: develop in the sporocyst of shistosomes, or rediae of other trematodes
• Mature cercariae leave the host snail and become free-living in the water
• Cercariae are tailed larvae (forked tail in Schistosomes)
• Cercariae infect the final host through skin penetration (Schistosomes) or by encysting as metacercariae on plants or in intermediate hosts
• Metacercariae are infective to humans when ingested via plants (F. hepatica, F. buski, W. watsoni), fish (C. sinensis, H. heterophyes) or crabs (P. westermani)
• Larval development involves asexual multiplication, where a single miracidium can produce millions of cercariae
• Cercariae is the infective stage in Schistosomes
• Metacercariae is the infective stage in other trematodes

Schistosomes (Blood Flukes)

• Dioecious trematodes causing Schistosomiasis (bilharziasis)
• Schistosomiasis: water-borne and affects millions yearly in Africa, Asia, and Latin America
• S. haematobium, S. mansoni, S. japonicum infect over 100 million each.
• S. mekongi and S. intercalatum are other species infecting humans
• Male worm is broader with a gynecophoric canal to hold the female
• Schistosomes were originally called Bilharzia, named after Theodor Bilharz in 1851
• Inhabit venous plexuses of definitive hosts

Schistosoma Haematobium

• Endemic to Nile Valley, Egypt for millennia
• Eggs found in Egyptian mummies from 1,250–1,000 BC
• Schistosome antigens found in mummies from 3,100 BC
• Described by Bilharz in 1851 in Cairo, life cycle by Leiper in 1915 in Egypt
• Entrenched Nile valley: also endemic in Africa and West Asia
• Found in Ratnagiri, south of Mumbai, India in 1952
• About 200 million are at risk, 90 million infected globally
• Adults live in vesical/pelvic plexuses of veins

Morphology of S. Haematobium

• Adult male
  • 10–15 mm long x 1 mm thick
  • Finely tuberculated cuticle.
  • 2 muscular suckers
  • Small oral sucker
  • Large ventral sucker
  • Gynecophoric canal extends behind ventral sucker
• Adult female
  • Long and slender, 20 mm x 0.25 mm
  • Cuticular tubercles confined to ends
  • Gravid: 20–30 eggs in uterus, up to 300 eggs daily
• Egg
  • Ovoid
  • About 150 µm x 50 µm
  • Nonoperculated
  • Brownish yellow transparent shell
  • Terminal spine at one pole (characteristic)

Egg Expulsion of S. Haematobium

• Eggs laid in vesical/pelvic venules or mesenteric-portal, pulmonary arterioles, ectopic sites
• Deposited with spine pointing posteriorly
• Migrate through vesical wall, spine pierces & lytic substances released
• Enter urinary bladder lumen, mixed with extravasated blood
• Discharged in urine, mainly at the end of micturition
• More eggs in urine midday
• Ectopic eggs die, evoke tissue reactions
• Found in rectal biopsies, rarely live in feces

Life Cycle of S. Haematobium

• S. haematobium completes its cycle in 2 hosts
• Humans are only definitive hosts (no known animal reservoir)
• Infective form: Cercaria larva
• Freshwater snails are intermediate hosts
• Urine-passed eggs embryonate in water to release ciliated miracidia
• Miracidia swim, penetrate snail tissues, reach the liver
• Bulinus snails in Africa, Ferrisia tenuis limpet in India, are intermediate hosts

Development in Snail

• Miracidia lose cilia, pass through 1st and 2nd-generation sporocysts for 4-8 weeks
• Asexual reproduction makes a large number of cercariae
• Cercaria has elongated ovoid body and forked tail (furcocercous cercaria)
• Cercariae escape the snail
• Cercariae swim in water for 1–3 days, penetrate unbroken skin of bathers through creating lytic substances

Development in Human

• Cercariae shed tails, become schistosomulae, enter peripheral venules
• Migrate through vena cava, right heart, pulmonary circulation, left heart, systemic circulation, to the liver
• Schistosomulae grow, become sexually differentiated adolescents (20 days after penetration)
• Migrate against bloodstream to inferior mesenteric veins, finally reaching the vesical and pelvic venous plexuses
• Mature, mate, start laying eggs
• Eggs appear in urine around 10–12 weeks after cercarial penetration
• Adult worms live for 20–30 years

Pathogenicity and Clinical Features of Schistosomes

• Classified by stages of infection:
  • Skin penetration and incubation
  • Egg deposition and extrusion
  • Tissue proliferation and repair
• Incubation:
  • Cercarial dermatitis (swimmer's itch, transient itching with petechial lesions)
  • General anaphylactic/toxic symptoms
  • More severe in visitors
• Anaphylactic/toxic symptoms:
  • Fever
  • Headache
  • Malaise
  • Urticaria
• Accompanied by:
  • Leucocytosis
  • Eosinophilia
  • Enlarged tender liver
  • Palpable spleen
  • More common S. japonicum (Katayama fever)
• Oviposition can cause:
  • Painless terminal hematuria (endemic hematuria)
  • Initial microscopic hematuria that becomes gross
  • Micturition frequency and burning
  • Cystoscopy
  • Hyperplasia
  • Inflammation of the bladder mucosa
  • Minute papular or vesicular lesions
• Clinical features during tissue proliferation and repair
  • Chronic stage marked by granular appearance of vesical mucosa (sandy patches) with fibrosis and hyperplasia
  • Dense infiltration with lymphocytes, plasma cells, eosinophils occurs at egg deposition sites causes pseudoabscesses
  • Trigone initially involved, entire mucosa becomes inflamed, thickened, and ulcerated
  • Secondary bacterial infection causes chronic cystitis
  • Calculi forms due to deposits of oxalate and uric acid crystals around eggs/blood clots in the bladder
  • May have obstructive hyperplasia (hydroureter) of the ureters and urethra
  • Chronic schistosomiasis is associated with squamous cell carcinoma of the bladder
  • S. haematobium, now classified as a human carcinogen
  • Bladder carcinoma is associated with schistosoma hematobium
  • Bile duct carcinoma due to clonorchis sinensis
  • Bile duct carcinoma due to Opisthorchis viverrini
• May significant disease may occur in the lungs and central nervous system
• Ectopic lesions to the spinal cord, skin, and genital organs exist
• Spinal cord ectopic lesions cause transverse myelitis-like syndrome
• Schistosomiasis favors urinary carriage of typhoid bacilli.

Laboratory Diagnosis of Schistosomes

• Urine Microscopy
  • Eggs with terminal spines shown microscopically
  • Centrifuged urine or filtration with nucleopore filters
  • More eggs at the end of micturition in blood and pus
  • Nucleopore filtration technique quantifies infection intensity
  • Eggs can be found in seminal fluid
• Histopathology
  • Diagnosis of infection by showing eggs in bladder mucosal biopsy
• Detection of Antigen
  • Detection via specific schistosome antigens is also possible through specific:
  • Circulating anodic antigen (CAA)
  • Circulating cathodic antigens (CCA)
• ELSA
• This test uses monoclonal antibodies with high sensitivity; only done in specialized labs
• Detection of Antibody
  • Can be detected with:
    • Complement fixation tests (CFT)
    • Bentonite flocculation tests
    • Indirect haemagglutination (IHA)
    • Immunofluorescence
    • Gel diffusion tests
  • Two serological tests at Centers for Disease Control and Prevention :
    • Falcon assay screening test (FAST) also called ELISA
    • Confirmatory enzyme-linked immunoelectrotransfer blot (EITB)
    • FAST shows the S. haematobium with high specific and sensitivity antibody(95-99%)
• Intradermal Skin Test (Fairley’s test)
  • Positive for all schistosomiasis. with antigen from infected snails, eggs, cercariae, adult worms in laboratory animals for the intradermal allegic test, using infected animals for antigen
• Imaging
  • Bladder/ureteral calcification X-ray of abdomen
  • Ultrasonography for:
    • Hydroureter
    • Hydronephrosis
    • Intravenous pyelogram (IVP) and cystoscopy in indirect diagnosis testing

Shistosome Treatment and Prophylaxis

• Preferred drug: Praziquantel
  • With the (40mg/kg for 1 day dose)
• Alternative for S. haematobium infections: Metriphonate
  • Given for (7.5 mg/kg weekly for 3 weeks)
• Prophylaxis against Schistosomes:
  • Eradicate the snails of infectious fluke.
  • Control spreading through human waste.
  • Treat those tested as being infected
  • Avoid entering contaminated waters

Schistosoma Mansoni

• Discovered due to the presence of eggs with lateral spines in a West Indian patient from then, it became known as to be named the S. mansoni
• Regions of distribution in Africa, South America, and the Caribbean islands.
• Habitat: Adult lives in inferior mesenteric veins along
• Similar to S. haematobium besides for other factors:
  • Smaller in size as adults with pointed tubercles
• Uterus only contains around 1-3 eggs/
• 4-5 week periods of time are needed for cercariae to penetrate to the start of production Lateral Spines and yellowish tint also

Schistosome Life cycle

• Hosts: Monkeys and baboons in endemic-prone regions along with humans as an optimal definitive variety of hosts.
• fresh-water snails of the Biomphalaria genus
• Fork-tailed infective properties
• As they grow to mature, they move toward liver arteries and the gut walls and through the venules
• Pass to lumens so that they can be transferred through feces

###Pathogenicity Aspects

• Following Skin Penetration through cercariae causes rash in localized areas
• Occurrences from the maturation of the liver for up to 4–8 weeks fever is at highest with individuals showing eosinophilia
• Egg Deposits will then turn into intestine and lead to bilharzasis so colicky pains arise
• eggs then lead to granulomas that cause portal hypertension

Diagnosis and Prevention

• Stool test
• Kato-Katx, tissue biopises will confirm antibody
• Prazinquantel is treatment with caution with snails.

Major Points for Schistosomes

• Dioecious forms of seperation
• The messenteric regions will be more suceptible and leaf body with bifurcated regions
• Defintive hosts- Humans Intermediate: Snail Infect: Tercaris and Swimer Treatment- Bathe and keep safe

Fasciola Hepatica

• Liver flukes
• Described almost 600 years ago in 1379
• Largest and most common liver region but primary host are domestic livestock like sheep
• Can lead to liver rod in stock

Morphology

• Adult worms are big and leaf like almost 5% inches or so
• It has rounded with oral sucker or 15 mm Can survive live up to 50 years

Hosts and Symptoms

• Sheep and Goats or limonea snials.
• Infection spreads as water beds are consumed
• Worms live out of passages and embryos or larvae escape before the snails mature
• The cercarie may survive long in water until those that develop.
• Acute phases leads to heptaomegaly or eosinophilia and then can persist through the gut causing damage and death.

Treatment and Prevention

• Bile extractions with eggs
• ELISA testing or the control with cleaning of waters.

Nematodes

• Class-worm which has threadlike appearance when earth worms may infect
• Parasites in water.
• Can cause swelling and cylindrical symptoms where the excretory regions have little to little.

Lifecycle

Phasmid and human as the final one.

Larva Migrans

• A loss of ability and the infection in dermis layers.

• Ascaris Lumbricaide

• Most common one of worms with high burden infection and sanitary issues will spread
• A trioral lip is formed around mouth
• Fertilized and unfertilized eggs exist.
• Can show no symptom in patient because it is small as the worms are in the lungs with a few to compare.
• Toxicity can infect at high.

###Trichuris

• Small with anterior, where most is in intestine with low.
• A triple shell forms around it with mucus when infection arrives in an acute format

Trichinella Spiralis

• Muscles and direct route to life cycle
• Female has a vivacious discharge
• There is a parasite with direct line of the species.

Diagnosis

• Smoking will harm and long term infection in lungs through muscle that is the main issue
• Spiral is a huge effect

• Strongyloidiasis

• Small body with long range effects on life cycle and is parasitic infection
• Is very unique and there are some who have infections that they have been made by certain factors:
• Skin infections
• Eggs can be found as there are constant signs with no direct host
• Hyperinfections may also occur.
• There, steriloids and immuno is required and if it has long prolonged time, than that will affect many points
• High levels of antibodies

• Diagnosis

• Sputum
• Stolls can be infected as to look
• A skin test can be done All of these should then be treated to those patients.