Listeria May Be a Cause of Early Undiagnosed Miscarriage

New research suggests the bacteria that causes listeriosis may be a bigger threat in early pregnancy than previously thought. Usually considered a danger to late pregnancy, scientists suggest early undiagnosed miscarriages could be caused, in some cases, by infection with Listeria.

Added to that, the bacteria Listeria monocytogenes sickens approximately 1,600 people each year, with about 1,500 hospitalizations and 260 deaths, according to the Centers for Disease Control and Prevention (CDC). Infection with the bacteria is where the name listeriosis comes in, and its impact on unborn children, the elderly, and those with compromised immune systems can be deadly.

Pregnant women are a high-risk group for listeria and are 10 times more likely than the general population to suffer listeriosis. The bacteria causes meningitis and contributes to sepsis, stillbirths, preterm labor, miscarriages, and potentially fatal infections in newborns.

While listeria is generally associated with harm during the third term of pregnancy, a new study published in the journal mBio charted the deadly path of listeria infection during early pregnancy through a study involving rhesus macaque monkeys.

Listeria May Be a Cause of Early Undiagnosed Miscarriage — *Image by James Archer, CDC/Public Health Image Library*

From Contaminated Food to Early Miscarriage

Listeria bacteria spreads primarily through contaminated food. For this study, four pregnant primates were inoculated with a virulent strain of L. monocytogenes isolated earlier from 11 pregnant women who had suffered stillbirth, premature labor, and miscarriage. The reproductive and immune system of macaques are similar to humans, offering a window into how listeria impacts early pregnancy.

From observation, blood, tissue, and microbe analysis, research authors found the following:

First trimester exposure to listeria consistently resulted in fetal death within one to two weeks of exposure.
The female monkeys suffered few, if any, symptoms.
Shedding of bacteria in the stool was first evident within five days in three monkeys. In the fourth, no bacteria was shed in the stool, yet fetal death still occurred.
In the infected female primates, high levels of L. monocytogenes were located in the placenta, less so in tissues outside the uterus.
The rate of fetal death for primates infected in this study during the first-trimester (100%) was higher than earlier studies that investigated infection during the third-trimester (30%). The study authors note that "the maternal-fetal interface in early pregnancy in the macaque is exquisitely sensitive to listeriosis."

Study authors suggest the speed and efficiency by which listeria causes fatal infection could be the reason for some human miscarriages that do not appear to have a cause. "There are effective antibiotics available. It is treatable. The issue is that because it's asymptomatic, the fetus may be infected by the time anyone realizes the mother was infected," noted graduate student and lead author in the study Bryce Wolfe, who studies cellular and molecular pathology at the University of Wisconsin-Madison, in a press release.

Protect Yourself Against Listeria

Whether or not you are planning on becoming pregnant, steer clear of certain foods to reduce your risk of contracting listeria. Although many individuals suffer no, or mild symptoms, others can suffer meningitis, and risk increases with age and chronic illness. Problem products include:

Soft cheeses: Cheeses like brie, and unpasteurized feta, are up to 160 times more likely to cause listeria. Be sure cheese is pasteurized and also avoid Camembert and quesco fresco, which is easily contaminated during production.
Unpasteurized milk: While raw milk may be trendy, it can carry a heavy host of pathogens including Salmonella, Listeria, Campylobacter, and Escherichia coli (E. coli).
Raw spouts and melons: The growing conditions for sprouts are the same for serious bacteria, like E. Coli and listeria. Avoid sprouts, even organic and home-grown, including clover, radish, alfalfa, and mung bean, unless they are thoroughly cooked to kill the bacteria. Rinse melons before cutting, throw away melons left at room temperature for more than four hours, and discard refrigerated, cut melon within seven days.

Deli meats, hot dogs, smoked fish: Deli and other compilation meats like hot dogs and sausages can be dangerous unless heated to an internal temperature of 165ºF. The same goes for meat spreads and lunch meats. Refrigerated smoked fish is risky as well.

For pregnant women, listeria can silently stalk an unborn baby. Reproductive physiologist and professor of comparative biosciences and obstetrics and gynecology at UW-Madison, Thaddeus Golos, remarked in the press statement:

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.

With continued research, study scientists hope to better understand how the bacteria so successfully targets the human reproductive system, and to apply that understanding to other serious maternal infections, including Zika.