Platehelminths Flashcards
Classification of Helminths
- Tapeworms (cestodes)
- Flukes (trematodes)
- Round worms (nematodes)
Tapeworms and flukes = platyhelminths (flatworms)
Definitions
Host: living organism on which the parasite lives and causes harm
Definitive host: organism in which the adult or sexually mature stage of parasite lives
Intermediate host: organism in which the parasite lives during a period of its development only
Reservoir host: source of infection and potential re-infection of humans and as a means of sustaining a parasite when it is not infecting humans
General characteristics of platyhelminths, hosts, diagnosis
Bilateral, symmetrical flattened worms
Definite head end
Lacking body cavity
Hosts: intermediate (larval stage), definitive (adult stae)
Diagnosis: microscopic examination of stool for eggs
Flukes (trematodes) - morphological features, general life cycle, examples
1cm long
Leaf-like
Hermaphrodite except blood fluke
Almost all have 2 suckers, oral (anterior) and ventral
General outline of life cycle
- egg (diagnostic stage) —-> sporocysts in intermediate host —-> metacercariae in 2nd intermediate host –> ingestion or skin penetration –> adult worm in definitive host
Examples (classification by habitat)
- blood fluke: schistosoma
- liver fluke: clonorchis sinensis
- lung fluke: paragonimus westermani
- intestinal fluke: fasiolopsis buski
Schistosomiasis - main species, life cycle
Disease also known as bilharzia
Blood flukes
2nd most important parasitic disease after malaria
Main species
- S. mansoni
- S. japonicum (china and SE asia)
- S. haematobium
- S. mekongi
Life cycle:
- eggs develop into cercariae in snail and released into water –> penetrate human skin –> mature into adults and migrate to portal blood then to
– mesenteric venules of bowel/rectum (all except S haematobium)
or
– venous plexus of bladder (S. haematobium)
Schistosomiasis - clinical features
3 stages
- dermatitis (penetrate skin): urticaria
- migration: fever, chills, GI upset, cough, eosinophilia
- chronic infection: egg deposition, GRANULOMATOUS tissue reaction
- -> liver (hepatosplenomegaly)
- -> cirrhosis (all except haematobium)
- -> bladder (haematuria, calculus, carcinoma – haematobium)
Schistosomiasis - diagnosis and treatment
Diagnosis
- stool or urine microscopy for parasite eggs
- rectal or bladder biopsy
Treatment
- PRAZIQUANTEL
- ->40 mg/kg/day in 1-2 doses for mansoni/haematobium
- -> 60 mg/kg/day in 2-3 doses for japonicum, mekongi
Clonorchiasis - transmission, prevalence
Clonorchis sinensis
Liver fluke
China, SE asia, Japan
Adult fluke infects biliary tracts
Transmission: raw, poorly cooked or salted/pickled infected FRESHWATER FISH
Clonorchiasis - clinical disease and complications
Asymptomatic (most cases)
Acute infection:
- fever, eosinophilia (inflammation and intermittent obstruction of biliary ducts)
- upper abdominal pain, hepatomegaly, obstructive jaundice
Chronic infection:
- recurrent cholangitis, pancreatitis
- risk of cholangiocarcinoma in long standing cases
Clonorchiasis - diagnosis and treatment
Diagnosis:
- stool for microscopy for presence of eggs
- endoscopy: duodenal aspirate for microscopic exam of eggs
- USG, CT, MRI imaging for fluke in bile ducts or gallbladder
- operative finding
Treatment:
- praziquantel PO 2 days
or
- albendazole PO 7 days
Paragonimiasis - transmission, clinical features, diagnosis, treatment
Paragonimus westermani
Lung fluke
China, SE asia, Japan
Transmission: ingestion of infected crustaceans (inadquately cooked or pickled crab/crayfish)
Clinical features
- light infections: asymptomatic
- acute symptoms: cough, abdominal pain, low grade fever (2-15 days after infection)
- long term:
- – mimic bronchitis or TB, cough with blood tinged sputum
- – CNS: epileptic seizures (rare)
- – GI: abdominal pain, bloody diarrhoea
- – Skin: subcutaneous nodules in lower abdomen (firm, mobile tender)
Diagnosis: stool or sputum for eggs
Treatment: Praziquantel
Tapeworm (cestodes) - general morphology, examples
Adult: ribbon-like flattened
No digestive tract
All adults worms are INTESTINAL parasites
3 parts:
- head (scolex) with organs of attachment, with hooks and suckers
- neck with actively dividing cells for growth and production of new segment
- body composed of multiple segments (proglottids)
Examples
- pork tapeworm: taenia solium/asiatica
- beef tapeworm: taenia saginata
- fish tapeworm: diphyllobothrium latum (B12 def)
- Hydatid disease: echinococcus
Taeniasis - epidemiology, transmission, clinical features, rare complications
T. solium: central and south america, africa, SE asia
T. saginata: worldwide wherever beef is consumed
Transmission: raw or undercooked beef (saginata) or pork (solium, asiatica)
Clinical features:
- mostly asymptomatic or mild – pass proglottids in faeces
- more symptoms in T. saginata (larger worm) – abdominal pain, LOA, LOW
Rare complications:
- tapeworm lodged in appendix, biliary ducts (obstructive symptoms)
- cysticercosis
Taenia solium - main complication and pathogenesis, clinical presentations, diagnosis, treatment, prevention
CYSTICERCOSIS
- ingestion of EGGS of T. solium by humans –> humans become accidental intermediate host (rather than pigs)
- larvae develop in humans = VERY SEVERE
Larva –> brain, muscles, skin, other tissues
- epilepsy or fatal encephalopathy (neurocysticercosis)
- muscle, eye, skin nodules
Diagnosis:
- intestinal taeniasis: hx of proglottids in faeces, stool for eggs/ proglottids
- cysticercosis: brain scan (CT, MRI, Xray) –> calcified cysts, radiological survey of skeletal muscles, serology
Treatment:
- Praziquantel
- Cysticercosis: Albendazole + Praziquantel
Prevention:
- consume thoroughly cooked pork only
- personal hygiene
Echinococcosis - transmission, species, clinical features
Hydatid disease/ Hydatidosis
Zoonotic infection caused by larval stage tapeworms
Worldwide, particularly sheep rearing areas
Transmission: ingestion of ova; humans are accidental intermediate host infected by close contact with infected dogs, foxes, wolves
Echinococcus granulosus: solitary cyst (cystic)
Echinococcus multilocularis: multiple cysts (alveolar)
Clinical features:
- most are asymptomatic
- slowly enlarging masses, most commonly affect liver and lung
- hydatid cysts in liver, lung, brain, bone –> local complications from pressure inflammation
- rupture and spillage of cyst fluid –> hypersensitivity
