The human family have bullet holes, he kileld them, not allowing zombification, this will be even worse if is discovered there is a actual cure or the people that are able to go around all variants already and he killed them for nothing.
The kid is likely a after apocalypse child, so she was possibly a variant but too young to show clear signs, that is if this zombie parasite did infect everybody alve and being able to keep consciousness and not rotting is a anomaly trait, maybe they were normal humans that survived for years..