11 - schistomes Flashcards
What is the global distribution of schistosomiasis?
Mostly found in Africa (especially eastern Africa) but it is also has low to moderate presence in parts of south america and Asia
What are some advantages of secondary hosts?
- increased reproductive potential, as a-sexual reproduction can occur in secondary hosts
- increases the range of the parasite in space and time
- the parasites can still survive when one host is scare
- an intermediate host can channel a parasite towards it’s definitive host
What are the three major factors responsible for maintaining schistosome transmission?
- pollution of water with urine/faeces containing eggs
- presence of a suitable host
- human contact with water infected with cercariae
How do cercarie locate the definitive host?
The use water turbulence and skin derived fatty acids and use their forked tail to swin towards the host
How do cercariae enter the human, once they’re located them.
The cercariae attach to the skin and use proteases to break through the epidermis. They then shed their glycocalyx (to avoid complement) and shed their tails to become schistosomula
What are the three developmental stages that schistosomula go through during migration?
Skin schistosomula, lung schistosomula and liver schistosomula (they mature in the liver)
What is the life span of an adult schistosome?
Up to 5 years (dependant on species)
Where are adult schistomes usually found in the human body?
The venous system (S. haematobium are found in the veins surrounding the liver, where as the other species are found in the veins surrounding the small intestines)
What is the main cause of pathology in a schistome infection
The immune response of the eggs which have been forced into tissues such as the intestine or the bladder
What are miracidia?
A motile, ciliates larval stage of schistosomes which are released when eggs hatch in fresh water and that infect snails
What are sporocysts and what is their role in the schistosome life cycle?
Sporocysts are a non motile form of schistosomes that develop from miracidium inside snail tissue. Secondary sporocysts produce numerous cercariae that can infect a human host when released from a snail.
What is the first clinical phase of human schistosomiasis and what is it caused by?
Cercarial dermatitis/ swimmers itch which is a rash caused by an allergic reaction as a result of cercariae burrowing through the skin
What are the common clinical features of acute schistosomiasis/katayama syndrome and what are the symptoms caused by?
- a dry cough, mild to moderate hepatosplenomegaly, fever, weight loss and giant hives
- caused by parasite maturation
What are the symptoms of an established infection of S. haemotobium?
- blood in the urine
- painful or difficult urination
- abdominal pain
- bladder inflammation
What are the symptoms of established infections of schistosomes such as S. mansoni?
- abdominal pain
- diarrhoea (That may be bloody)
- Hepatomegaly (sometimes with splenomegaly)
