Made it possible for mob to be infected with several viruses at once.

code/game/objects/effects/decals/Cleanable/humans.dm

@@ -11,7 +11,7 @@
 	random_icon_states = list("floor1", "floor2", "floor3", "floor4", "floor5", "floor6", "floor7")
 	var/list/viruses = list()
 	blood_DNA = list()
-	var/datum/disease2/disease/virus2 = null
+	var/list/datum/disease2/disease/virus2 = list()
 	var/amount = 5
 
 /obj/effect/decal/cleanable/blood/Del()
@@ -144,4 +144,4 @@
 	icon = 'blood.dmi'
 	icon_state = "mucus"
 	random_icon_states = list("mucus")
-	var/datum/disease2/disease/virus2 = null
+	var/list/datum/disease2/disease/virus2 = null

code/game/objects/items/devices/scanners.dm

@@ -129,7 +129,7 @@ MASS SPECTROMETER
 	if (istype(M, /mob/living/carbon))
 		if(M:reagents.total_volume > 0)
 			user.show_message(text("\red Warning: Unknown substance detected in subject's blood."))
-		if(M:virus2)
+		if(M:virus2.len)
 			user.show_message(text("\red Warning: Unknown pathogen detected in subject's blood."))
 	if (M.getCloneLoss())
 		user.show_message("\red Subject appears to have been imperfectly cloned.")