CCL2 and infection: As shown in Additional file 1: Fig. S10, cytokines in the brain (TNF-α, CCL-2, CXCL-2, CXCL-10, IL-1β, IL-6, IL-17, and M-CSF) were upregulated after infection at 3 dpi, and the cytokine content gradually decreased with extension of the infection time.