Several species can be infected by Listeria monocytogenes, among them birds, fishes, shellfish and crustaceans, but most cases of clinical listeriosis have been reported in bovines, ovines and caprines. Listeriosis can brake out sporadically. Clinical manifestations in animais inelude encephalitis in adults, septicemia with focal hepatic necrosis in young ruminants and no ruminants, abortion, especially in sheep, goats and cows, premature childbirths or dead fetuses, mastitis and conjunctivitis. The primary manifestaron of this disease in pigs is the septicemia, being less frequent encephalitis and abortion. On the other hand, although birds are subclinical carriers, sporadic cases of listeriosis have been described, being more frequent septicemia and less common meningoencephalitis. Some evidences indicate that hay and grass silage have been sources of listeriosis, however, some authors have contemplated the possibility of venereal transmission. The intestinal mucous is the most common road of entrance, after the oral ingestion in the case of septicemic and abortive listeriosis. It is difficult to find data on the economic impact of the listeriosis. Nevertheless, this should not be the only motive to improve detection, disinfection and handling methodologies of the microorganism. It is also necessary to consider a possible connection between the animais and its role as carrier or infection source for humans, which could occur as a result of direct contact or by consumption of contaminated food of animal origin.