C9 and mastitis: TMEM154 has been shown to be associated with reduced susceptibility to peste des petits ruminants virus [43] and ovine progressive pneumonia virus in sheep [44]; C9 plays an important role in the immune response to sheep mastitis [45]; ZNF283 is involved in the interaction between foot-and-mouth disease virus and the host [46] and can inhibit the production of porcine reproductive and respiratory syndrome virus and the synthesis of viral RNA [47]; and PRNP is associated with resistance to scrapie in sheep [48].