The Pennsylvania Department of Agriculture issued a consumer alert yesterday regarding the consumption of raw milk from a Pennsylvania dairy:

Consumers who have purchased raw milk from Misty Meadow Farm in Bernville, Berks County, any time after April 16 should discard it immediately due to the risk of Listeria contamination, Agriculture Secretary Dennis Wolff said today.

Raw milk is milk that has not been pasteurized or homogenized.

"During routine inspection of the dairy, a preliminary test showed the presence of Listeria bacteria in some raw milk samples," said Wolff. "If consumers have raw milk from this farm, they should discard it immediately."

Listeriosis is the disease caused by Listeria monocytogenes. It is acquired by the ingestion of contaminated foods. Certain groups of individuals are at great risk for listeriosis. These are pregnant women (and their unborn children) and immunocompromised persons (e.g., transplant recipients). Among infants, listeriosis occurs when the infection is transmitted from the mother, either through the placenta or during the birthing process. These host factors, along with the amount of bacteria ingested and the virulence of the strain, determine the risk of disease.

Listeria can invade the body through a normal and intact gastrointestinal tract. Once in the body Listeria bacteria can travel through the blood stream, but are often found inside cells (they are "intracellular" pathogens). Listeria can co-opt the cell’s machinery to its own advantage by manipulating the host cell genes, and then move directly from cell-to-cell, avoiding many of the host’s defense mechanisms5. The bacteria also produce toxins that damages cells.

For unknown reasons, in immune-deficient hosts Listeria invades and grows best in the central nervous system, causing meningitis and/or encephalitis (brain infection). In pregnant women, the fetus is most heavily infected, leading to spontaneous abortion, stillbirths, or sepsis in infancy.

Every year in the U.S. approximately 2,500 cases of Listeriosis are known to occur4. (It is likely that more cases go unrecognized). About 500 deaths per year are attributed to listeriosis6. These statistics indicate true misfortunes, as listeriosis is a preventable condition.

Learn more about Listeriosis at the About-Listeria Web site.