Something is moving in that stool ...

This patient developed bloody stool whilst on holiday in Africa. They continue on return home and he undergo a flexible sigmoidoscopy. Of course, stool samples are obtained (last image).
WHAT IS THE PATHOGEN?

a) Clostridium difficile

Can be seen moving down a microscope

b) Salmonella enterica

Can give bloody diarrhoea but its not it!

c) Entamoeba histiolytica

Rasberry stool, to be examined warm

d) Campylobacter jejuni

May also give bloody stool but that's not it

e) Vibrio cholerae

Hmm, rice-water stool...

explanation

Let me give you some more clues! Classically, there are 'flask-shaped' ulcers found on resectional histology in which the mucosal surface ulcer is rather narrow with a wider, necrotic submucosal component in which the amoeba multiply. Stools have been described as like "Raspberry jam" and when examined whilst still warm, something can be seen moving. Of course PCR is the best way of confirming the diagnosis. 

This patient had amoebic dysentery!  Mild cases can resolve without metronidazole.