Understanding health effects of listeria – Part 1

What is listeria (1)

Listeria monocytogenes (Listeria) is a food-borne disease-causing bacteria; the disease is called listeriosis.

Listeria can invade the body through a normal and intact gastrointestinal tract.

Once in the body, Listeria can travel through the blood stream but the bacteria are often found inside cells.

Listeria also produces toxins that damage cells.

Listeria invades and grows best in the central nervous system among immune compromised persons, causing meningitis and/or encephalitis (brain infection).

In pregnant women, the fetus can become infected, leading to spontaneous abortion, stillbirths, or sepsis (blood infection) in infancy.

Approximately 2,500 cases of listeriosis are estimated to occur in the United States (U.S.) each year.

About 200 in every 1000 cases result in death.

Certain groups of individuals are at greater risk for listeriosis, including pregnant women (and their unborn children) and immune-compromised persons.

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. Human cases of listeriosis are, for the most part, sporadic and treatable.

Nonetheless, Listeria remains an important threat to public health, especially among those most susceptible to this disease.

Listeria is often isolated in cattle, sheep, and fowl, and is also found in dairy products, fruits, and vegetables.

What are the symptoms of listeria infection?

It is thought that ingestion of as few as 1,000 cells of Listeria bacteria can result in illness.

After ingestion of food contaminated with Listeria, incubation periods (from time of exposure to onset of illness) are in the range of one to eight weeks, averaging about 31 days.

Five days to three weeks after ingestion, Listeria has access to all body areas and may involve the central nervous system, heart, eyes, or other locations.

• Dr Anthony Nwaoney is a Consultant