Parasitic Platyhelminths - Trematodes

Trematodes general description

Small dorso-ventrally flattened, non-segmented, worms with simple anatomy.

All digenea (trematode subclass) are parasitic with 2 suckers that they use to attach Whitin the host
→ Oral sucker contains the mouth whose muscular pharynx allows it to pump food into its blind-ending gut

All hermaphrodites except schistosomes

Many have actin spines that help the worms anchor themselves

General treatment of Platyhelminths

Praziquantel → Paralysis of musculature

Describe liver flukes

Fasciola hepatica: agent of fascioliasis

Found in bile ducts, gallbladder, and pancreas

Large (3-5 cm)

-Multibranched uterus is situated under the abdominal sucking disk
-Testis are branched too and located in the middle part of the body

Liver fluke life cycle

Mainly:

• We acquire the Encysted Metacercaria on aquatic plants/ plants near water bodies

• It excysts in the duodenum

• Adults are the form found in the hepatic ducts

• We (and mammals) shed unembryonated eggs in feces

F. hepatica clinical presentation

Migration through the liver causes symptoms proportionate to worm burden

General symptoms: Fever, abdominal pain, diarrhea, eosinophilia

Heavy infection → Epithelial hyperplasia and fibrosis

Biliary obstruction due to worms can lead to cirrhosis

Fascioliasis diagnosis

Unembryonated eggs in feces

Fascioliasis prevention

Avoiding aquatic vegetables

Chinese or Oriental liver fluke

Clonorchis sinensis

Parasite of man, dogs, and cats, and EXTREMELY common southeast Asia

C. sinensis life cycle

Mainly:

• We ingest the Metacercariae form in the flesh or skin of freshwater fish

• Excystation occurs in the duodenum

• Adults are found in biliary ducts

• Embryonated (unlike fascioliasis) eggs are passed in feces

Clonorchiasis clinical presentation

Irritation and inflammation of the bile ducts leading to their dilation and the formation of Pigmented Gallstones

Liver: Enlarged, necrotic, tender and high ALT/AST

Lung flukes general description

Paragonimus westermani agent of paragonimiasis

Asia, Africa, South America

Plump reddish-brown, oval

Paragonimus westermani life cycle

Mainly:

• We ingest crustaceans bearing the encysted form: Metacercariae

• They excyst in the duodenum

• Adults are found in lungs, where they lay eggs which are then excreted in the sputum or re-swallowed and passed in stools

• The form in stools is embryonated eggs

Lung fluke disease clinical presentation

Adult worms in the lungs get encapsulated in granulomas (often 2 at a time), Rupture can result in:

• Dry cough

• Blood-stained rusty-brown sputum

• Inflammation of the pleural membrane

*Note: X-ray looks like X-rays for T

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Chronic high worm burden can result in:

• Chronic bronchitis

• Dyspnea

• Fibrosis

Cerebral paragonimiasis symptoms

Granulomatous abscesses → Epilepsy, headaches, fever, nausea, vision impairment, seizures

Paragonimiasis diagnosis

• Eggs in sputum or stool samples

• May take biopsy to look for eggs in tissues

• Serology

Blood flukes description

Schistosoma spp - agents of Schistosomiasis (Bilharziasis)

Female is long and slender, male is thick and shorter, and forms a characteristic groove in which the female reposes

Schistosoma life cycle

Mainly:

1. Eggs released from humans

2. Eggs mature in the marine environment (Snail involvement)

3. Snails eventually release the Cercariae form, which has a bifurcated tail (like fish) and is capable of free-swimming

4. Cercariae penetrates the human skin and loses its tail becoming a schistosomulae that can travel hematogenously to the liver

5. Reach adulthood in liver

6. Paired male and female adults will migrate to different sites depending on the specie:

   1. S. japonicum and S. mansoni worms will migrate to the mesenteric venules of the bowel/rectum

   2. S. haematobium

Schistosoma virulence factors

• Collagenases

• Eggs have spines that facilitate their retention

• Necrosis-causing enzyme releases leads to the release of the eggs into the intestines or bladder

Schistosomiasis clinical presentation

• Type 1/4 Hypersensitivities

• Schistosoma dermatitis

• Acute schistosomiasis:

  • Cough

  • Hepatosplenomegaly (Hyperplasia to make up for lack of blood flow)

  • Lymphadenopathy (due to obstructions)

  • Eosinophilia

• Chronic schistosomiasis

  • S. japonicum / mansoni:

    • Hepatosplenomegaly

    • Portal hypertension

    • Esophageal varices

  • S. haematobium:

    • Inflammation & fibrosis

    • Obstruction

    • Uremia

    • Hydronephrosis

    • Pulmonary hypertension

    • Risk factor for Squamous Cell Carcinoma of the Bladder

Diagnosis of schistosomiasis

Diagnose different species depending on spine position

S. haematobium: Apical spine
S. mansoni: Lateral spine
S. japonicum: Vestigial spine

H→M→J (Straight→Diagonal→Useless)

Schistosomiasis prevention

Avoid sewage water