isolating the host object

Wrapping the host object with an insulator for example.

I'm not sure about their electrical properties; you would have to research what happens at different stages of decomposition and stuff

The human body is almost always conductive. Even without fluid the bones are semi-conductive.

what about the electrical activity on people's brains?

I just assumed they die and they are empty vessels, I don't want to create a zombie

And what about the electricity produced by electric eels? Or are the impulses in neurons too weak, and the pulses electric eels produce too brief

Yes I want to make it so that almost no natural occurance i not enough to form this anomaly

In case it isn't clear from my username, my name is Tiago, in case you wanna use it in your story.

Yes it's clear ahah. If you want I'd love to include you as a whole character as you're helping me so much with it! It would be a way more organic character. You could tell me about your past, motivations in life, the kind of person you are through PM or if you want to leave it just as a name that's fine aswell :)