Listeria may pose a greater health risk during early-stage pregnancy than previously reported

Researchers from the University of Wisconsin–Madison School of Veterinary Medicine (USA) have published results demonstrating that infection by the bacterium Listeria monocytogenes during early pregnancy can cause a greater risk of miscarriage and other neonatal complications than previously thought

The team utilized a primate model of the infection in order to observe the effects that the bacteria have on the developing fetus. It was previously known that the bacteria are dangerous in the third trimester of pregnancy; however, as corresponding author Ted Golos reported: “What wasn’t known with much clarity before this study is that it appears it’s a severe risk factor in early pregnancy.”

The study, conducted using macaques, saw pregnant animals infected with a low dose of bacterial culture not dissimilar to what would be found in contaminated food. The infection was monitored through fecal and blood samples and the fetus examined through ultrasound.

After 7–13 days post-infection the macaques experienced fecal shedding, maternal bacteremia and intrauterine fetal death. The tissues were then harvested and researchers demonstrated that bacterial burden was lowest in the maternal tissues, higher in the placenta and endometrium, and highest in the fetus. They went on to suggest that the immune mechanisms that the mother uses protects her own tissues but affects the placenta, leaving the fetus in a vulnerable state, a process also of relevance to other infections, such as Zika.

Bryce Wolfe, the lead author of the study concluded: “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.”  This may suggest that many miscarriages that were thought to not have a cause may have been due to Listeria infection.

The team now intends to continue their research to better define host—pathogen interactions at the maternal—fetal interface.

Source: Wolfe B, Wiepza GJ, Schotzko M, et al. Acute Fetal Demise with First Trimester Maternal Infection Resulting from Listeria monocytogenes in a Nonhuman Primate Model. mBio. doi: 10.1128/mBio.01938-16 (2017);


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