Listeria monocytogenes

Prepared by: Michael J. Huerkamp, DVM, Diplomate ACLAM
Date: April 2, 1999

Agent: Listeria monocytogenes

Listeria monocytogenes causes listeriosis – a rare disease, primarily foodborne, in infant or elderly humans. The bacterium has been found in unpasteurized milkd and a variety of raw foods, such as uncooked meats and vegetables, as well as in processed foods that become contaminated after processing, such as soft cheeses and cold cuts at the deli counter. In addition, many animals carry Listeria monocytogenes in their feces as a normal bowel inhabitant. Animals may be experimentally infected with Listeria monocytogenes in order to study the biology of the organism, immune responsiveness of the host, or to develop tests for diagnosis.

Potential Hazard: The bacterium may be present in the feces, brain, spinal cord of viscera of infected animals. Shedding in the feces can occur for a lengthy period of time. Listeria infection usually occurs in the outer lining of the brain. However, other body systems may be affected. The signs of human illness include headache, fever, nausea, vomiting, weakness and/or diarrhea. Abortion may occur in pregnant women. Humans usually acquire the organism from contaminated food or secondary to poor personal hygiene practices.

Recommended Precautions: The animal biosafety level II practices (DAR SOP 400-3) will protect husbandry personnel against exposure or infection. Vaccines are not available for use in humans.

References: MMWR 41(15): 251, 257-8, 1992.
Blood DC, Radostits OM. Veterinary Medicine, 7th ed., Bailliere-Tindall, 1989, pp. 582-7.