Ma'anar ƙamus na "Harrin Halittu" yana nufin sakin kwayoyin halitta da gangan, kamar kwayoyin cuta, ƙwayoyin cuta, ko gubobi, da nufin cutar da mutane, dabbobi, ko tsire-tsire. Wadannan hare-haren na iya faruwa ta hanyoyi daban-daban, ciki har da gurɓatar abinci da ruwan sha, watsar da wakili kai tsaye zuwa cikin muhalli, ko ta hanyar amfani da dabbobi masu kamuwa da cuta a matsayin vector. Sakamakon harin halitta na iya kamawa daga rashin lafiya mai sauƙi zuwa barkewar cututtuka da kuma yawan mace-mace.