Trematodes (Flukes)

Aspect Details

Phylum Platyhelminthes (Flatworms)

Common Name Flukes

Body Structure Bilaterally symmetrical, leaf-like or elongated, with suckers for

attachment

Life Cycle Complex, requiring multiple hosts (definitive and intermediate

hosts)

Hosts Involved Definitive host (usually vertebrates), intermediate host (typically

mollusks)

Transmission Ingestion of contaminated food, water, or through direct contact

with infected water

Reproductive System Hermaphroditic (in most species); some have separate sexes

Eggs Operculated, which allows them to hatch under specific

conditions in water

Larval Stages Miracidium, sporocyst, redia, cercaria, metacercaria (depending

on species)

Habitat in Host Varies depending on species: liver, intestines, blood vessels,

lungs, etc.

Common Diseases Fascioliasis, Schistosomiasis, Paragonimiasis, etc.

Symptoms Abdominal pain, diarrhea, jaundice, or respiratory symptoms

(dependant on species)
 Diagnosis Identification of eggs in stool/urine, imaging techniques (e.g.,
ultrasound, CT scan)

Treatment Praziquantel, Albendazole, Triclabendazole (depending on

species)

Prevention Avoiding raw or undercooked aquatic food, improving sanitation

Study Table: Paragonimus westermani (Oriental Lung Fluke)

Category Details

Common Name Oriental Lung Fluke

Definitive Hosts Humans, cats, dogs, wild carnivores

1st Intermediate Host Antemelania asperata, Antemelania dactylus (snails)

2nd Intermediate Host Sundathelphusa philippina (mountain crab)

Paratenic Hosts Wild boars (less common)

Mode of Transmission Ingestion of raw/undercooked infected crab or crayfish

Habitat in Host Lung parenchyma (also ectopic: brain, skin, abdomen, etc.)

Morphology (Adult) Reddish-brown, coffee bean-shaped; 7–12 mm x 4–6 mm

Egg Morphology 80–118 µm × 48–60 µm, yellow-brown, thick shell, flattened

operculum, abopercular thickening

Life Cycle Highlights Egg → Miracidium → Snail (sporocyst → rediae → cercariae) →

Crab (metacercariae) → Human ingestion → Excyst in
duodenum → Peritoneum → Diaphragm → Lungs (adults)

Prepatent Period 65–90 days

Pathogenesis Fibrotic cysts with adult worms and eggs in lungs; ectopic
migration possible

Pulmonary Symptoms Chronic cough, hemoptysis, chest pain, dyspnea, low-grade

fever

Ectopic Manifestations Cerebral paragonimiasis (seizures, hemiparesis), cutaneous

(migrating nodules), abdominal, ocular, cardiac, etc.

Diagnosis (Microscopy) Eggs in sputum, stool, or aspirates; best with NaOH

concentration method

Radiologic Findings Cavitary/nodular infiltrates, pleural effusion (often mimics TB)

Hematology Eosinophilia, ↑IgE (esp. in acute stage)

 Serology ELISA (96–99% sensitivity), Immunoblot, CF test, Intradermal
test

Molecular Tests LAMP assay – field-friendly DNA detection tool

Neuroimaging (Cerebral cases) CT/MRI: grape-cluster ring-enhancing lesions with edema

Treatment (First-line) Praziquantel: 25 mg/kg TID × 2–3 days

Alternative Drugs Triclabendazole (single dose, better compliance); Bithionol

(alternative)

Prevention Avoid raw/undercooked crabs, proper cooking, health education

Epidemiology (Philippines) Endemic in Sorsogon, Mindoro, Samar, Leyte, Zamboanga del

Norte, Basilan, Davao Oriental, Cotabato

Associated Cultural Practices Consumption of raw crabs in dishes like kinagang, kinilaw,
sinugba

Common Misdiagnosis Often misdiagnosed as pulmonary tuberculosis (PTB) due to

overlapping symptoms and radiologic features

Fasciolopsis buski, Fasciola hepatica, and Fasciola gigantica

Feature Fasciolopsis buski Fasciola hepatica Fasciola gigantica

Common Name Giant intestinal fluke Sheep liver fluke Tropical liver fluke

Habitat in Humans Small intestine Bile ducts of liver Bile ducts of liver

Definitive Hosts Humans, pigs Sheep, cattle, humans Cattle, sheep, humans

Intermediate Host Planorbid freshwater snail Lymnaeid snail (e.g., Lymnaea Lymnaeid snail (e.g., Lymnaea
truncatula) auricularia)

Infective Stage Metacercaria Metacercaria Metacercaria

Mode of Transmission Ingestion of metacercaria on Ingestion of metacercaria on Ingestion of metacercaria on

aquatic plants aquatic plants aquatic plants

Egg Morphology Large, oval, operculated; Large, oval, operculated Similar to F. hepatica
indistinct from Fasciola spp. (similar to F. buski)

Adult Morphology 2–7.5 cm long, no cephalic 2–3 cm long, with cephalic Larger than F. hepatica (up to
cone cone 7.5 cm), broader

Pathology Inflammation, ulceration, Biliary obstruction, hepatitis, More severe hepatic damage
intestinal obstruction liver cirrhosis due to larger size

Geographic Distribution Southeast Asia Worldwide (esp. temperate Africa, Asia (tropical areas)
zones)

Diagnosis Stool: eggs indistinguishable Stool, serology Stool, serology

from Fasciola
 Treatment Praziquantel Triclabendazole (drug of Triclabendazole
choice)

Clonorchis sinensis vs. Opisthorchis spp.

Feature Clonorchis sinensis Opisthorchis felineus Opisthorchis viverrini

Adult Morphology Elongated, flat, ~10–25 mm Similar to C. sinensis but Similar to O. felineus but
long; oral sucker small, ventral slightly shorter; testes lobed generally smaller (7–12 mm);
sucker slightly larger; two (not branched); shape more testes lobed and tandem
highly branched testes in slender
posterior end

Egg Morphology 27–35 µm × 11–20 µm; Very similar to C. sinensis; Eggs similar to other two;
operculated; prominent slightly smaller and narrower minor size variation makes
shoulder; small knob at species differentiation by egg
posterior end morphology difficult

Geographic Distribution East Asia (China, Korea, Eastern Europe, Russia, Southeast Asia (Thailand,
Vietnam) Siberia Laos, Cambodia)

Intermediate Hosts 1st: Bithynia snails; 2nd: 1st: Bithynia tentaculata; 2nd: 1st: Bithynia siamensis
freshwater fish (cyprinids) freshwater fish goniomphalos; 2nd: freshwater
fish

Definitive Hosts Humans, dogs, cats Humans, carnivorous Humans, dogs, cats
mammals (dogs, cats, foxes)

Pathology Chronic infections: cholangitis, Similar to C. sinensis; may Closely associated with
bile duct obstruction, induce liver damage and cholangiocarcinoma,
cholangiocarcinoma inflammation especially in endemic areas

Diagnosis Fecal examination for eggs; Egg detection; species Same as O. felineus;
serology/PCR for confirmation differentiation difficult on molecular methods for specific
morphology alone ID

Schistosoma spp. (Blood Flukes)

(From Belizario & Paniker)

Feature Schistosoma japonicum Schistosoma mansoni Schistosoma haematobium

Common Name Oriental blood fluke Manson's blood fluke Vesical blood fluke

Geographic Distribution Philippines, China, Indonesia Africa, South America, Africa, Middle East
Caribbean, Middle East

Definitive Hosts Humans, pigs, dogs, cats, Humans Humans

rodents, cattle

Intermediate Host Oncomelania hupensis Biomphalaria spp. (snail) Bulinus spp. (snail)
quadrasi (snail)

Mode of Transmission Skin penetration by cercariae

in freshwater
 Habitat in Host Mesenteric venules of small Mesenteric venules of large Venous plexus of urinary
intestine intestine bladder

Egg Morphology Ovoid, small lateral spine or Oval, lateral spine Oval, terminal spine
hook; 46–110 × 37–90 µm

Egg Route of Exit Feces Feces Urine

Pathogenesis Granuloma formation around Granulomas in liver and Granulomas in bladder wall →
eggs → hepatosplenic intestines → hepatosplenic hematuria, bladder fibrosis,
disease, CNS lesions, schistosomiasis squamous cell carcinoma
pulmonary hypertension

Acute Phase Katayama fever (fever, Similar acute syndrome Similar acute syndrome
malaise, eosinophilia)

Chronic Disease Hepatosplenomegaly, portal Hepatosplenomegaly, portal Bladder wall fibrosis,

hypertension, cor pulmonale, hypertension obstructive uropathy, bladder
seizures (cerebral cancer
schistosomiasis)

Diagnosis (Direct) Kato-Katz (stool), MIFC, rectal Kato-Katz (stool) Filtration of urine, microscopy
biopsy

Diagnosis (Serology) COPT, ELISA, IHA ELISA, IHA ELISA, IHA

Treatment Praziquantel 60 mg/kg (2 Praziquantel 40 mg/kg (1–2 Praziquantel 40 mg/kg (1–2

doses) doses) doses)

Prevalence in PH Endemic in 28 provinces; most Not endemic in PH Not endemic in PH

important species in PH

Snail Control & Prevention Sanitation, health education,

snail habitat modification,
molluscicides, GIS mapping

Unique Features Smallest eggs; zoonotic; can Largest lateral spine among Only species excreted in urine;
cause cerebral and pulmonary schistosome eggs associated with bladder cancer
lesions

Heterophyes heterophyes vs. Haplorchis taichui

Feature Heterophyes heterophyes Haplorchis taichui

Group Intestinal fluke (Heterophyid) Intestinal fluke (Heterophyid)

Transmission Ingestion of metacercariae in Same

undercooked fish

Definitive Hosts Humans, dogs, cats, birds Humans, dogs, cats, birds

1st Intermediate Host Snail (species varies: freshwater, Melania juncea (brackish water snail in
brackish, or marine) PH)
 2nd Intermediate Host Fresh/brackish/marine fish (under scales, Same; over 30 fish species reported in PH
muscle, etc.)

Adult Size < 2 mm, pyriform or oval < 2 mm, elongated

Morphology Scale-like spines; gonotyl near left ventral Same; sometimes less prominent gonotyl
sucker border

Testes Posterior; various arrangements Same

Ovary Globular/slightly lobed; submedian Same

pre-/post-testicular

Egg Morphology Ovoid, operculated, light brown, 20–30 × Same

15–17 μm

Egg Features Smooth operculum, no abopercular knob; Same; indistinguishable from

symmetrical miracidium Clonorchis/Opisthorchis

Life Cycle Notes Cercariae from snails encyst in fish Same; often base of fins
muscles, fins, scales

Site of Adult in Host Small intestine Small intestine

Pathogenesis Mucosal burrowing, inflammation, excess Same; PUD/APD-like symptoms, colicky

mucus, ulcer-like symptoms pain, mucoid diarrhea

Severe Manifestations Eggs may embolize to heart, brain, spinal Same

cord

Diagnosis Stool exam (Kato thick > formalin-ether), Same; distinguish from
PCR in low burden Clonorchis/Opisthorchis

Treatment Praziquantel 25 mg/kg TID × 1 day Same

Epidemiology Egypt, Israel, India, China, Korea, Japan, Philippines (Compostela Valley), emerging
Philippines in 8 Mindanao provinces

Prevalence (PH) Previously low (<1% nationwide) Up to 31% in Monkayo, Compostela

Valley

Reservoir Hosts Dogs, cats, birds Same

Prevention & Control Avoid raw/undercooked fish, lab Same; surveillance in raw fish–eating
surveillance, education regions (e.g., kinilaw areas)

Echinostoma ilocanum vs. Artyfechinostomum malayanum

Feature Echinostoma ilocanum Artyfechinostomum malayanum

Group Intestinal fluke (Echinostome) Intestinal fluke (Echinostome)

Transmission Ingestion of metacercariae in snails (2nd Same

intermediate host)

Definitive Hosts Humans, pigs, dogs, cats, rats Humans, pigs, dogs, cats, rats
1st Intermediate Host Gyraulus convexiusculus, Hippeutis Not identified in PH (likely same as E.
umbilicalis ilocanum)

2nd Intermediate Host Pila luzonica, Vivipara angularis Lymnaea cumingiana, Ampullarius
canaliculatus

Adult Size 2.5–6.6 mm (L) × 1–1.35 mm (W) 5–12 mm (L) × 2–3 mm (W)

Shape Tapered posterior end Rounded posterior end

Collar Spines 49–51 43–45

Testes Deeply bilobed, tandem in third quarter 2 large testes, each with 6–9 lobes,
arranged in tandem

Ovary In front of anterior testis Small, rounded, pre-equatorial

Egg Morphology Straw-colored, 83–116 × 58–69 μm Golden brown, 120–130 × 80–90 μm

Egg Features Operculated, indistinct from Same

Fasciola/Fasciolopsis

Site of Adult in Host Small intestine Small intestine

Pathogenesis Ulceration, inflammation, diarrhea Same

(sometimes bloody)

Diagnosis Detection of eggs in stool Detection of eggs in stool

Treatment Praziquantel 25 mg/kg TID for 1 day Same

Epidemiology (PH) Northern Luzon, Leyte, Samar, Mindanao Northern & Central Luzon, Siargao Island

Reservoir Host Likely rats Likely rats

Prevention & Control Avoid eating raw/undercooked snails (2nd Same

intermediate hosts)