Influenza Viruses and Amplifier Hosts

Different species have different thresholds for how much of a particular virus they have to be exposed to before they get infected. An amplifier host is one in which the virus like replicates often at an accelerated rate and like spews forth at extremely high levels. Ebola could literally be on a syringe that was used three days ago and there's just the tiniest, tiniest amount of disease on it.