Listeriosis

Listeriosis occurs in a variety of animals including humans, and most often affects the pregnant uterus, the central nervous system (CNS) or the bloodstream. During pregnancy, infection spreads to the foetus, which will either be born severely ill or die in-utero. In non-pregnant animals, listeriosis usually presents as meningitis, encephalitis. In humans, infection most often occurs in the immunocompromised and elderly, and to a lesser extent the pregnant woman, the unborn, or the newly delivered infant. Infection can be treated successfully with antibiotics, however 20–40% of human cases are fatal..

In domestic animals (especially in sheep and goats) listeriosis usually presents as encephalitis, abortion, or septicaemia, and is a cause of considerable economic loss.

The genus Listeria comprises six species of Gram-positive bacteria. Almost all cases of listeriosis are due to Listeria monocytogenes although up to 10% of cases in sheep are due to Listeria ivanovii.

Listeriae are ubiquitous in the environment worldwide, especially in sites with decaying organic vegetable material. Many animals carry the organism in the faeces without serious infection. The consumption of contaminated food or feed is the principal route of transmission for both humans and animals, however other means of transmission occur.

Human listeriosis is rare (<1 to > 10 cases per million people in North America and Western Europe), but because of the high mortality rate, it is amongst the most important causes of death from food-borne infections in industrialized countries. In the UK, human listeriosis is the biggest single cause of death from a preventable food-borne disease. Listeriosis in domestic animals is a cause of considerable economic loss. Control measures should be directed towards both to exclude Listeria from food or feed as well as inhibiting its multiplication and survival. Silage which is spoiled or mouldy should not be used, and care should be taken to maintain anaerobic conditions for as long as possible.

Dietary advice is available for disease prevention, particularly targeted at ‘at risk’ individuals to modify their diet to avoid eating specific foods such as soft cheese and pâté.