July 15, 2019

Why are Pregnant Women So at Risk for Listeria Infections?

The ongoing Listeria monocytogenes outbreak linked to commercially prepared, prepackaged caramel apples and that may be associated with plain apples packed by Bidart Brothers has sickened 32 people and killed seven. Ten of these illnesses were in pregnant women; one woman suffered a fetal loss. Why is this infection so serious in pregnant women?

Pregnant womanOne theory is that in pregnancy, the immune system is suppressed so the body doesn’t reject the embryo and fetus. This reduction in immunity may be why these women are so susceptible to listeriosis and why the complications can be so severe. Researchers at Berkeley, however, discovered that Listeria monocytogenes bacteria use the immune system suppression to invade the placenta where they are protected from the mother’s immune system.

Once the bacteria are in the placenta, they can grow rapidly, then emerge to infect the maternal liver and spleen. One theory is that miscarriage occurs as a defense mechanism so the body is protected from the source of the bacteria’s growth. It is difficult for any bacteria to cross the placental barrier, but once they do, complications can be very serious. Scientists think that the bacteria can cross the endothelium of the maternal blood vessels, and get into the fetal circulatory system of the placental villi.

In most people, most Listeria bacteria that get into the body are destroyed in the liver. But some can hide out in cells called hepatocytes in the liver. This leads to “hepatocyte lysis” and the bacteria are then released in large numbers into the bloodstream. The bacteria can also hide out in macrophages, a type of white blood cell, where they are protected against immune response and some antibiotics.

Children, the elderly, and those with chronic illness or compromised immune systems are also more susceptible to Listeria infections because of suppressed immunity and other problems with the liver and other organs. People who have undergone organ transplants, those with liver and kidney disease, diabetes, and AIDS are also at greater risk for complications from a Listeria infection.

The time it takes for the bacteria to reproduce in hepatocytes and macrophages, and the time it takes to get into the placenta, reproduce, and emerge into the blood stream may be why the incubation period between exposure to Listeria monocytogenes and the onset of symptoms is so long. The incubation period can range from three days to 70 days. Most pregnant women become ill about six weeks after infection. Knowing this time frame will help doctors trace back the food or water that is the source of the bacteria.

Pregnant women should always be careful about what they eat to avoid any food poisoning, especially listeriosis. Common advice is to avoid eating deli meats, smoked meats, undercooked and uncooked eggs, undercooked and raw meat and seafood, raw milk, sprouts, raw milk cheeses, soft cheeses, and unpasteurized cider. These products are all susceptible to bacterial contamination, especially Listeria bacteria. And since Listeria bacteria can grow at refrigerator temperatures, all of these foods are risky. Wash all produce thoroughly, and avoid cross-contamination between uncooked meats, seafood, and eggs and foods eaten raw.

In the current outbreak, if you ate any commercially prepared, prepackaged caramel apples this fall or winter, monitor yourself for the symptoms of listeriosis. They include high fever, severe headache, muscle aches, confusion, diarrhea, nausea, and stomach and abdominal cramps. Pregnant women, unfortunately, may only have a very mild flu-like illness, but listeriosis can cause stillbirth, miscarriage, and infection in the newborn baby that can be very serious.

If you do get ill, treatment is available. It’s important to get to your doctor as soon as you suspect something is wrong to receive antibiotic treatment.


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