06. Trematodes (Schisto) Flashcards
What is an example of a blood fluke? where are they found?
Schistosoma - in blood vessels
What is an example of a lung fluke? where are they found?
Paragonumus - in lungs
Whta is an example of a liver fluke? Where are they found? (5)
Largel liver fluke - Fasciola hepatica, Fasciola gigantica
Small liver fluke - Opisthorchis, Chlonorchis, Dicrocoelium
Found in the liver
How many intermediate hosts does Schistosoma have
1
What causes Schistosomiasis?
human acitivities, water
What are other names for Scistosomiasis?
Bilharziasis
Snail fever
Katayama fever
What is common in the geographic areas where schistosomisis is found, in terms of human habits? (3)
- Fresh surface waters are used for bathing or washing
- waters are contaminated with human feces or urine
- certain types of snails are present to host the intermediate stages of the parasite
What are the ways in which schisto are unusual trematodes? (4)
- They are called digeneic trematodes because they have 2 hosts (one intermediate and one definitive) rather than 3+
- They are dioecious rather than hermaphroditic
- They (the cercaria stage) infect their DH by directly penetrating the body surface rather than being eaten (the other ones it is by eating/drinking water, plants, animals (meat))
- They parasitize the intravascular niche (blood vessels, urinary bladder and hepatic portal system)
What kind of uses of water causes infection of schistosomes
- Water used for recreational purposes
- Water used for washing vegetables, fruits, clothes, dishes, etc…
What is the intermediate host of S. mansoni?
Biomphalaria
What is the intermediate host od S. haematobium?
Bilinus
What is the intermediat host of S. japonicum?
Oncomelina
What kind of schistosomiasis is caused by S. mansoni?
Intestinal schistosomiasis
Where is the parasite S. mansoni found in infection?
the mesenteric vein and the portal venous system
What is the basic pathological lesion of S. mansoni?
egg granuloma in the liver and colon
What are characters of acute schistosomiasis?
fever
enlarged and tender liver
desentery
eosinophilia
What are characters of chronic schistosomiasis?
asymptomatic intestinal or symptomatic hepatosplenic
What kind of schistosomiasis is caused by S. haematobium?
urinary schistosomiasis
Where is the parasite S. heamatobium found in infection?
the vesical and pelvic plexuses
What is the main pathologic lesion of S. haematobium?
egg granuloma
What is known as a major consequence of urinary schistosomiasis?
Squamous cell bladder carcinoma
What kind of schistosomiasis is caused by S. japonicum?
Oriental schistosomiasis
Where is the parasite S. japonicum found in infection?
inhabiting the superior and inferior mesenteric veins
Which schistosome is the most pathogenic among the ones that can infect humans?
S. japonicum
Who is infected by S. bovis and where in the world does this occur?
- normally infecting cattle, sheep and goats in Africa
- parts of southern Europe and the Middle East
Who is infected by S. rodhaini and where in the world does this occur?
- normally infecting rodent and carnivores
- in parts of Central Africa
What is Schistosomaisis’s rank in terms of socio-economic important?
- second after malaria
What age group is most often affected by schisto?
children under 14
What are the symptoms of Schisto?
- Amdominal pain, cough, diarrhea, fever, fatigue
- Eosinophilia: high eosinophil and granulocyte (WBC) count
- Skin symptoms: at the start if infection, mild itching and a paplar dermatitis of the feet and other parts after swimming in polluted streams containing cercaris
- Hepatosplenomegaly: enlargement of both the liver and the spleen (S. mansoni, S. japonicum)
- Genital sores: lesions that increase vulnerability to HIV infection. Lesions caused by schistosomiasis may continue to be a problem after control of the scistosomiasis infection itself. Early treatment, especially in children, which is relatively inexpensive, prevents the formation of the sores. (S. haematobium)
How is a Schisto infection diagnosed?
Microscopic examination of:
- stool - S. mansoni, S. japonicum
- urine - S. haematobium
What are the acute pathologies of Schisto?
- Cercarial dermatitis
- Katayama fever
What is Cercarial dermatitis?
Skin rash occurs upon massive penetration of skin by cercaria. This can lead to lesions at the site of penetrations
What is Katayama fever?
- It is a systemic hypersensitivity reaction against the migrating schistosomua. The disease, which consists of fever, fatigue and muscle pain starts a few weeks or even months after a primary infection
- Most patients recover spontaneously after 2 to 10 weeks - The disease occurs after a primary exposure
What are the chronic pathologies of schistosomiasis?
- Direct morbidity resulting from pathological changes and clinical manifestations induced by the deposition of eggs in tissues followed by the inflammatory immune reaction. This may cause hepatosplenomegaly, hepatic fibrosis, diarrhea and blood in the stool
- Additional morbidity such as anemia and growth retardation
What is the pathology of hepatosplenomegaly?
- It is a delayed type of hypersensitivity reaction resulting in severe pathology in the liver
- It appears to be a necessary host protective response against the soluble egg antigens secreted by the entrapped egg which are hepatotoxic (toxic to the liver)
- The granuloma consists mainly of a number of T and B lymphocytes, macrophages, eosinophils and other cells of the immune system
Describe the immune response to Schosiosomiasis
- Chronic morbidity in schistosomiasis is not due to the adult worms but the immune response of the host to the eggs trapped in tissues
- The trapped eggs secrete a range of molecules stimulating the CD4+ T-cell (T-helper cell) resulting in the formation of the granulomatous inflammation
- The T-helper cells secrete IL-13 and when it is bound to its receptor promotes the formation of the granuloma
- Schistosomes are complex organisms and so is the immune aspect of the host-parasite relationships
- Schistosomes have developed strategies to manipulate and/or escape the immune response of the host. For example, egg antigens supress cell-mediated immunity
