Listeriosis is caused by the bacterium , Listeria monocytogenes. The bacteria are found in soil and water. Vegetables can become contaminated from the soil or from manure used as fertilizer. Livestock become contaminated after eating contaminated silage or water. Unpasteurized milk, or foods made from unpasteurized milk may also contain the bacterium.
Occurrence is worldwide.
The incubation period ranges from 3 to 70 days, with the median incubation estimated at 3 weeks. A person with listeriosis usually has fever, muscle aches, and sometimes, nausea and vomiting. The bacteria may infect the brain and the membrane lining the brain causing meningoencephalitis. The onset of meningoencephalitis may be sudden, with fever, intense headache, nausea, and vomiting. Infected pregnant women may have minimal symptoms, characterized by a mild flu-like illness.