Medical Parasitology: Lecture 17: Platyhelminths 1

Helminths

Parasitic worms.

What’s in the Phylum Platyhelminths?

Flatworms

Phylum Platyhelminths: Features

Bilateral symmetry, ectoderm, mesoderm, and endoderm.

No body cavity or coelom- acoelomate.

Cephalization.

Mouth and gut, but no separate anus.

No circulatory or respiratory system.

Flatworms

Flukes (trematodes), monogeneans (fish parasites), and tapeworms (cestodes).

Class Trematoda

Aspidogastrea (parasites of fish). Digneans = Dignetic Trematodes (flukes).

Trematode Features in Life Cycle

Complex life cycles almost always involving a mollusk and a vertebrate. Adults are usually hermaphroditic.

Schistosoma spp AKA

Schistosomiasis.

Where does Schistosoma spp live?

In copula in blood vessels.

Schistosomiasis

Biharzia = snail fever

What are the 6 species of Schistosomiasis that affect humans?

S. mansoni

S. japonicum

S. haematobium

S. intercalatum

S. mekongi

S. guineensis

Schistosoma mansoni Distibution

Mostly Sub Saharan Africa. Some in South America and SW Asia.

Schistosoma japonicum Distribution

China and Philippines. Eradicated from Japan.

Schistosoma haematobium Distribution

Mostly Sub Saharan Africa. Some foci in SW Asia (Yemen).

Schistosomiasis- Diagnosis

Finding eggs in feces (S. mansoni and S. japonicum).

Finding eggs in urine (S. haematobium).

Anti-schistome antibodies.

Circulating worm or egg antigens.

S. mansoni Symptoms/Pathology.

Eggs become trapped in tissues.

Triggers granuloma formation (attempts to isolate infection).

Damages and enlarges liver, spleen and intestinal wall.

Impedes blood flow causing hypertension.

Distended abdomen.

Fatigue, diarrhea and dysentery.

Impaired growth and cognitive development in children.

What does S. mansoni trigger?

Granuloma formation (attempts to isolate infection).

What does S. mansoni damage?

Liver, spleen and intestinal wall.

What does S. mansoni enlarge?

Liver and spleen.

What does S. mansoni impede?

Blood flow causing hypertension.

S. mansoni Treatment and Control

Different drug target adults vs. juvenile worms (praziquantel and artemisinin).

Snail control using molluscicides.

Improved sanitation.

Avoiding excreting eggs into snail habitats

S. japonicum Symptoms/Pathology.

Similar to S. mansoni. Worse pathology due to higher egg production rate (1300-1500 eggs/day).

Eggs often appear in brain causing cerebral schistomiasis.

Acute form: Katayama fever (fever, chills, nausea, abdominal pain, rashes).

S. japonicum Treatment and Control

Same drugs as for S. mansoni.

Control more challenging due to multiple vertebrate hosts.

Snails are amphibious.

Avoid using night soil fertilizer.

S. haematobium Symptoms/Pathology.

Eggs trapped in bladder wall.

Infections with hematuria.

Long term infection associated with squamous cell carcinoma in the bladder.

Damage to ureters.

Increased susceptibility to HIV.

Hydronephrosis

Dilation of kidney.

Pyelonephritis

Bacterial infection in kidney.

S. haematobium Treatment and Control

Hematuria as an easy way to identify likely infection.

Population based treatment for control.

Educating children not to urinate into water.

Molluscicdes.

Schistomiasis Vaccine

Infection infers some partial immunity.

Light infections are usually asymptomatic.

Attenuated cercariae.

Vaccine are in human trials.

What does Fasicola spp cause?

Fasicoliasis.

What are the two Fasicola spp types?

Fasicola hepatica and Fasicola gigantica.

Fasicola spp: Fasicola hepatica: Distribution

Europe, Oceania, Americas, Africa, and Asia.

Fasicola spp: Fasicola gigantica: Distribution

Africa and Asia.

Where does Fasicola spp live?

In the liver of sheep, cows, and can inhabit humans.

How does Fasicola spp spread?

By adaptation to more snail hosts and movement of livestock.

How does Fasicoliasis cause anemia?

By worms burrowing into liver parenchyma.

In Fasicoliasis, what does worms in bile duct cause?

Inflammation and obstruct flow of bile (jaundice and impaired lier function).

What does Fasicoliasis damage?

Gall bladder.

Fasicoliasis: Treatment/Control

Anti-helminth drugs.

Avoid eating plants nearby susceptible snails and affected livestock.

What does Paragonimus westermani cause?

Paragonimiasis.

What are Paragonimus westermani?

Lung flukes.

Paragonimiasis.: Early Stage

Abdominal pain, fever, diarrhea, chest pain, and fatigue.

Paragonimiasis.: Established Stage

Pulmonary paragonimiasis. Cough, blood in sputum, bronchitis, wheezing, cough, and shortness of breath.

Paragonimiasis- Diagnosis, Treatment, Control.

Cough and blood in sputum.

Eggs in sputum or feces.

Cysts often seen in chest radiograms/MRI scans.

Serologic tests (check for antibodies in blood).