ESR1 and infection: We therefore studied the expression of some genes coding for some steroidogenic enzymes (cyp11b1 and cyp19a1a and cyp19a2) and estrogen receptors (era, erb1 and erb2) in the testis, the main organ that synthesizes biologically active steroids de novo [60], and brain, as the brain is the main target tissue of the virus, of both species upon in vivo infection and in the testis upon in vitro infection.