(Yes it is a very old question but I can't resist posting an answer here...)
Not all amoeba are parasites. The common one that cause amoebiasis is Entamoeba histolytica, which can cause diarrhea in some infested individuals. Note that
infested is not equivalent to
infected. There are many types of bacteria colonizing the gut without causing any problems, including those contained in probiotics. Therefore it's really not necessary for the immune system to clear E. histolytica from the gut.
E. histolytica is normally separated from the gut
mucosal lining (surface) by the mucus layer, with or without secreted antibody. If it managed to penetrate that mucus layer, E. histolytica can start digest the
extracellular matrix (the matrix between cells) and cause a whole lot of problem. In response the gut cells will secret cytokines e.g.
IL-8 to recruit immune cells. That's when the original question's condition would occur, but it'd be more like a combined arms of immune cells against an army of amoeba...
Among the immune cells,
neutrophils, the most abundant leukocyte, are the first to arrive the battlefield.
They are numerous but ain't particularly "strong" or large. They can't
phagocytize (eat) the amoeba, but they can still kill amoeba by releasing
reactive oxygen species (basically the action is similar to bleach). However, more
virulent species of amoeba can kill neutrophils very effectively, as well as protecting themselves from neutrophils.
Before other components of the immune system are activated,
amoeba casualty ratio may be as high as
3000:1, but with other components of immune system the host would survive...
Moonah SN, Jiang NM, Petri Jr WA. Host immune response to intestinal amebiasis. PLoS pathogens. 2013 Aug 22;9(8):e1003489.