There are 6 species of Listeria bacteria. They are known as saprophytes in soil. [[Listeria monocytogenes|L.monocytogenes]] and [[Listeria ivanovii|L.ivanovii]] are pathogens carried by sheep and goats and shed in faeces and milk especially during stress. They can cause septicaemia, encephalitis, abortion and endophthalmitis in ruminants. Outbreaks of [[Listeriosis|Listeriosis]] often linked to silage feeding.