Probiotics will feed protozoa (blasto) infections however a short term use of them may be necessary to reset the intestinal environment. Probiotics will not kill the parasite, however short term use should help the intestinal environment. sIga is secretory immune globulins that are necessary for intestinal health, please see this link http://pptu.lefora.com/2011/08/20/secretory-iga-siga/
The problem with blasto is that it is a diverse organism where sub types exist and for each sub type there is a different treatment option. For instance if you had sub type 1, it may be killed by another drug combination. See badbugs.org for the different combinations.
I host another forum for protozoa parasites at pptu.lefora.com - we do not have much on blasto but there are some other resource material available. Let me know if I can help you any further.