The mean incubation period of ∼229 days that we measured for Tg(M83+/−:Gfap-luc+/−) mice after intraperitoneal challenge with 50 μg of α-synuclein fibrils is surprisingly similar to the incubation time after intracerebral inoculation (∼216 days) of the same mouse line with 30 μl of a 1% brain homogenate from sick TgM83+/+ mice, implying that intraperitoneal infection can be very efficient in causing disease (17). This evidence concerns the gene SNCA and infection.