From what I understand about it, any reptile can be infected with Entamoeba invadens, however Rhacodactlyus geckos are particularly susceptible to it while most other reptiles are not. That is not to say that your ball pythons that died did not die from it--you cannot rule it out without having had a necropsy done. It is possible that your snakes that died, did die from it and that one or more of your other snakes could have it and that there was some recent cross contamination which infected your geckos with it. Or, the snakes that died had it, your geckos contracted it from them at the time, but it did not cause an issue until now. Sometimes it can lie dormant in Rhacs until they experience stress, are placed together for breeding or the temperatures start to rise in the spring and their bodies begin to prepare for breeding. So, my best advice would be to get fecals done on all of your snakes and to practice very strict quarantine procedures with the geckos that you are currently treating.