An infectious disease of humans and animals caused by the bacteria Listeria monocytogenes and L. ivanovii. Both humans and animals can be carriers, which excrete the bacterium in feces. Sheep, goats, and cattle can excrete the bacteria in milk, without clinical symptoms of mastitis. The most important pathway of infection is probably through food. Listeria monocytogenes has frequently been isolated from grass silage (fermented fodder), especially from silage of inferior quality, which is an important source of infection in ruminants. Relatively few animals develop clinical disease, but a high proportion can be latent carriers. Humans most likely ingest the bacteria with contaminated food, such as meat and meat products, raw milk and milk products, and unwashed vegetables.

Encephalitis is the most common form of disease in ruminants, and septicemia with involvement of several organs, including the pregnant uterus, occurs most commonly in monogastric animals, including very young sheep, goats, and calves.

Most human cases are sporadic, but food-borne epidemics occur. Abortions, perinatal disease, and disease in immunosuppressed individuals are most common. Perinatal disease is dominated by septicemia, widespread microscopic abscesses, and meningitis. In adults, meningitis is by far the most common manifestation, but in immunosuppressed individuals encephalitis occurs, possibly with a pathogenesis similar to encephalitis in ruminants.

Clinical diagnosis is based on symptoms, on isolation of L. monocytogenes, and on histopathological examination of affected tissue, especially brain tissue. Medical bacteriology