Several studies add support to the above scheme: firstly, APOE has been found to modulate severity of disease (or susceptibility to infection) in the case of several diseases of microbial cause, including two caused by HSV1 and herpes simplex virus type 2 (HSV2)—namely, herpes labialis (Itzhaki et al., 1997) and genital herpes (Jayasuriya et al., 2008). The gene discussed is APOE; the disease is infection.