That's exactly how God slayed the firstborn because they were infected by the last of the grain that was tainted which was saved just for them.

You're issue is not with me but with cause and effect how God slayed the first born. You really should read Colin J. Humphreys' book Miracle of Exodus. He's a brilliant scholar who has explained most of the events in Exodus.

Since this explanation makes the most sense how God did it and you presented no better alternative then you're just blowing smoke.