Contributor: Gordon K. Klintworth
Listeriosis is a bacterial infection caused by Listeria monocytogenes.  Human infection usually presents as bacteremia (sometimes with septicemia), meningitis, or meningoencephalitis. An uncommon presentation is a characteristic encephalitis involving the brain stem, which is frequently fatal. Risk factors are an immunodeficiency state due to disease or therapeutic agents (leukemia, lymphoma, rheumatoid arthritis, organ recipients), pregnancy and the elderly. Infection acquired during pregnancy can cause abortion, fetal death and neonatal infection. A disseminated infection causes multiple microabscesses or granulomas. Giant cells are usually absent in the granulomas. Oculoglandular listeriosis is a rare manifestation that may follow infection from animals in which fever is associated with Parinaud ocular glandular syndrome.