New research conducted at the University of Wisconsin-Madison and published in the journal mBio has found that Listeria monocytogenes food poisoning can be a serious miscarriage threat in early pregnancy. Scientists at the university’s school of veterinary medicine studied how pathogens affect fetal development and change pregnancy outcomes.
Dr. Ted Golos, a UW-Maidson reproductive physiologist and professor of comparative biosciences and obstetrics and gynecology said, “for many years, Listeria has been associated with adverse outcomes in pregnancy, but particularly at the end of pregnancy. What wasn’t known with much clarity before this study is that it appears it’s a severe risk factor in early pregnancy. It’s striking that mom doesn’t get particularly ill from Listeria infection, but it has a profound impact on the fetus.”
Listeriosis sickens about 1600 Americans every year. The people who get sickest from this type of infection are the elderly and newborn babies. Pregnant women usually don’t get very sick if they contract listeriosis, but they can suffer premature birth, miscarriage, or stillbirth. Babies can even be born seriously ill with listeriosis.
Dr. Charles Czuprynski, a UW-Madison professor of pathobiological sciences and director of the UW-Madison Food Research Institute said, “the problem with this organisms is not a huge number of cases. It’s that when it is identified, it is associated with severe outcomes.”
Many foods can cause serious illness in pregnant women. As a general rule, they are advised to avoid unpasteurized milk, raw cider, soft cheese, sprouts, melons, and some deli meats because of the threat of Listeria and other types of pathogenic bacteria that can be in those products. And there is zero tolerance for Listeria in ready to eat foods for exactly this reason.
Dr. Sophia Kathariou, a North Carolina State University professor of food science and microbiology, gave the researchers a strain of Listeria that caused miscarriage, stillbirth and premature delivery in at least 11 pregnant women in 2000. Four pregnant rhesus macaques at the Wisconsin National Primate Research Center were fed doses of Listeria that were comparable to what may be in contaminated food.
Bryce Wolfe, lead author of the study who is a UW-Madison graduate student studying cellular and molecular pathology, monitored the speed and progression of the bacteria’s spread. Czuprynski said, “the animal ingested it; she tracked it being shed in fees and showing up in the bloodstream. They did ultrasound analysis of the fetus, and could then show events in terms of where the organism was preceding fetal demise.”
None of the monkeys showed any obvious signs of infection or illness before their pregnancies ended. Samples taken after intrauterine fetal death showed that the bacteria had invaded the placenta and the endometrium, which is the lining of the uterus. Wolfe said, “in that region, there’s a rich population of specialized immune cells, and it is exquisitely regulated. When you introduce a pathogen into the midst of this, it’s not very surprising that it’s going to cause some sort of adverse outcome disrupting this balance.”
Researchers think that inflammation caused by the maternal immune response to the fast-moving Listeria affects the placenta, stopping it from protecting the fetus. The placenta usually acts as a barrier against bacteria and harmful substances, but the researchers think that the mother’s immune system’s attempt to clear the bacteria actually damages the placenta, leaving the fetus open to harmful bacteria and toxins.
The researchers think that Listeria monocytogenes bacteria, and perhaps other pathogens, may be the cause of some miscarriages that are undiagnosed. The bacteria is so quick to reproduce and spread that it is hard to control. And because the mother’s illness is so mild and she may even be asymptomatic, the fetus may be infected before the mother even knows she is sick.
Listeriosis is treatable, but only if it is diagnosed. Sometimes, doctors have their patients take a prophylactic course of antibiotics if the woman has eaten food that may be contaminated with Listeria bacteria.