Early progression of infected design was start from small idea : fungal can infect human brain and can be control him or her. The ideas literally swapped idea of zombie virus with fungal infection. The idea was pretty new and unique and can be done if you check discovery channel that show as an reference how fungal things attack ants and insects. Early design start with couple restrictions of the rules. First, it must look realistically freaky but not goofy look. Second, it should away from pirate of the caribbean's dutch ship crews. Third, it doesn't nervelessly to be nasty gore look but can be beautiful somehow.