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The blood fluke story - labwork in the field

Posted by Anouk Gouvras on May 19, 2014 6:42:13 PM

Jambo from Tanzania,

 

I realise I'm a bit late with this post so lets get straight to it. Just a warning though, this will be a rather disgusting post so get ready to be grossed out.

 

You'll remember from my previous post about our school visits that we collect stool samples from infected children. This is because we collect the miracidia larval stage that hatches out of the parasite eggs. And these eggs come out with stool.

 

The blood fluke life cycle - a recap

 

Schistosoma. The worm pair releases schistosome eggs into the blood system. The eggs pierce through the wall of the intestinal/urinary tract and exit the host when he/she defecates or urinates. They reach fresh water and hatch out into a larval stage called miracidia.

 

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Life cycle of Schistosome, blood fluke parasite and the specimens we collect during our fieldwork (circled in yellow).

 

So in order to collect miracidia we need stool from infected children. Diagnosis of infection is achieved using the Kato Katz method: a specimen of stool viewed on a microscope slide. If schistosome (blood fluke) eggs are observed in the stool specimen then the person is infected with at least one pair of schistosomes. For more information on diagnosis have a look at this video.

 

Collecting eggs from stool

 

Once we know which kids are infected we go to the schools and get stool samples (see previous post). We take these back to the lab and then a long process of stool filtering begins. We filter the stool for schistosome eggs, these we place in water and light. This induces them to hatch out into miracidia. We collect the miracidia onto special cards that store their DNA. We transport these back to the UK.

 

We use a pair of filters called Pitchford funnels (devised by Pitchford & Visser). The inner smaller funnel has bigger pores that allow the schistosome eggs to pass through but stops larger pieces of stool. The outer funnel is made of a finer mesh with pores that stop schistosome eggs from going through, this allows us to pour lots of water through the funnel thereby washing the eggs of stool material that may stop them from hatching.

 

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Pitchford Funnels (devised by Pitchford & Visser). Credit Fiona Allan.

 

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Stool Samples. Credit Fiona Allan.

 

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Sieve to break up stool. Credit Fiona Allan.

 

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Using the sieve to break up the stool sample.

 

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Pouring stooly water through Pitchford Funnel. Credit Fiona Allan.

 

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Myself and Mr John processing stool samples. Credit Fiona Allan.

 

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Adding formalin to left over stool samples to kill of anything inside. These are disposed of safely later. Credit Fiona Allan.

 

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>Revocatus adding formalin to stool. Credt Fiona Allan.

 

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My Nagai releasing the eggs and some water into a petri dish.

 

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Petri dishes of eggs and water. Waiting to hatch.

 

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Fiona starts checking for miracidia swimming in the petri dish.

 

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Fiona and James in the lab in National Institute for Medical Research in Mwanza.

 

Sometimes out in rural areas where we use local hospitals to process our samples things can go wrong, such as a power cut. No electricity means no light through the microscope. Thankfully we rise to the challenge and strap our head torches round our microscopes as an alternate source of light. Not quite as clear but it still works.

 

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Even a power cut will not stop us, we use our head torches as a light source and continue working.

 

So that's it for now. Tune in for the next post - snail collecting on the banks of Lake Victoria.

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