Hytadid cysts Flashcards
Describe the echinococcus parasite - structure, prevalence, and its transmission.
- Most unpleasant of flatworm parasites as it forms larval cysts (what happens sometimes in T.solium)
- Atypical parasite as humans are not the definitive host, which are canines.
- Humans have become hosts via zoonosis – unnatural.
- It was endemic all over the world – New Zealand, Iceland, and tropics. It has now been eradicated via control of dogs.
- The adult cestode is very small, only a few mm long with a few segments (but very populous) and is found in gut of canines while the larval stage (hytadid cysts) are large and found in wide range of vertebrates – sheep, camels, goats and humans.
- The Turkana tribe in north Kenya have strong relationship with dogs and hence have a high incidence of Hytadid cysts.
Transmission –>
– Echinococcus infections spread to humans/other intermediate hosts via canine faeces or contaminated food or water.
– The eggs have an outer membrane which allows it to survive for months/years.
Describe the echinococcus life cycle.
– The adult tapeworm is found in canine, where it attaches to small intestine and produces lots of eggs in canine which enter environment via its faeces.
Intermediate host:-
- The eggs are then eaten by the intermediate host via faecal-oral transmission – these can include sheep, camels, goats and humans.
- The eggs will hatch within the intestine of the intermediate host to release oncospheres which will penetrate the gut and enter the bloodstream.
- The oncosphere will be swept around the body until it develops into the larval stage called a hytadid cyst.
- The cyst is unilocular – spherical with a thick outer membrane that surrounds a fluid filled cavity.
- They grow slowly and brood capsules inside will contain hundreds of protosclices (larvae) which each can give rise to an adult worm.
- The hytadid cysts can reside in livers, lungs and other organs. The consequences a cyst will have on health depends on its size and the organ in which they develop – e.g a small cyst in liver wouldn’t cause much harm but could be fatal in the brain.
What are the two main echinococcus species in humans and what kind of disease do they cause?
- Echinococcus granulosus - causes cystic echinococcosis.
2. Echinococcus multilocularis - causes alveolar echinococcosis.
Describe features of cystic echinococcosis - prevalence, pathology, diagnosis and treatment.
- Most common form of human echinococcus.
- Results in cystic echinococcosis, here the cysts are very obvious/discrete.
- Adult present in intestine of canines and larvae stages are in different vertebrates as listed above.
Prevalence
– Widely distributed parasite infection all over the world, including the Mediterranean coast, Middle East, South America, new Zealand, parts of Africa and Europe. In sheep farming regions.
Pathology –>
- cysts can cause damage to the affected organs – cysic echinococcus.
- e.g. in liver where they can result in biliary obstruction, cirrhosis.
- In the lungs they can lead to obstruction of the bronchials.
- In the brains there could be obstruction of CSF flow leading to hydrocephalus.
- If the cyst ruptures it will release a lot of foreign material in the body and could lead to anaphylactic shock. Therefore during treatment care is taken not to damage cysts.
Diagnosis is via imaging of the cysts – by CT scans, ultrasound, radiographs and MRI. Serological tests such as ELISA are used to confirm results. Ultrasound is preferred as it cheap and gives instant results.
The distinct cyst like structure makes it easier to identify.
Treatment is via the removal of the hytadid cysts from the organs. Surgery is 90% effective but can be risky depending on skills of professionals involved and risk of infection as well as location, size and age of the cyst. Albendazole can be used on smaller cysts, but on larger cysts surgery are needed – chemotherapy can then be used to prevent reoccurrence.
Describe the features of alveolar echinococcosis.
Causes alveolar echinococcosis, the cysts are not discrete/obvious – more virulent than cystic form.
– Adult forms are in found in the small intestines of foxes and dogs while larvae stages are in different rodent species (they are intermediate hosts). Parasite transmission is heavily affected by predator-prey relationship.
Prevalence
- Much more rare in humans but its prevalence is increasing. Found in cold climates with a high prevalence in Alaska, Siberia and Northern China.
- Emerging due to the breakup of the Soviet Union, as pockets of deprivation have emerged in former soviet states.
- Simultaneous occurrence of granulosis and multilocularis can occur very rarely in endemic areas of both forms, such as in western china.
Pathology
- Here the hytadid cysts have much thinner walls than granulosus that will develop and spread in hosts liver’s by penetrating through intestinal walls.
- They grow much more slowly, like a slow-growing malignant tumour. The cysts here will contain a mass of separate vesicles with gelatinous instead of fluid.
- Cysts have been likened to neoplasms, as they will break off and metastasise into other parts of the hosts’ body and sometimes form cysts in alveoli regions which can be fatal.
Diagnosis –> is difficult since the cysts are not discrete and protoslices may not be seen. Ultrasound is often complemented by a CT scan, with confirmation by serological tests.
Treatment is not effective –> mortality is 60-70% after treatment and 100% without. Surgical removal and chemotherapy for up to 2 years is the only effective procedure.
– > Prevention only ways to control.
E.g. the fox population in Europe is increasing and poses as problem to eradication of the parasite.
Both human Echinococcus forms are becoming more prevalent in many European countries due to fox populations and there seems to be fox-rodent cycle emerging.
