Pregnant women have an increased severity of infections with some organisms, including influenza virus, hepatitis E virus, herpes simplex virus, and malaria parasites. A new review on this topic includes an update on immunologic alterations during pregnancy.
Pregnant women are more severely affected by infections with some organisms, including influenza virus, hepatitis E virus, and herpes simplex virus, and malaria parasites. The evidence is more limited for organisms that cause coccidioidomycosis, measles, smallpox, and varicella. The threshold for diagnostic evaluation, as well as hospitalization and treatment, may be lower for pregnant women than for other patients, and this factor may bias some of the reports of increased disease severity.
• How does pregnancy impact the severity of influenza infection?
Pregnant women are at increased risk for severe illness from influenza virus infection. Cardiopulmonary adaptive changes occurring during pregnancy, such as increased heart rate and stroke volume and reduced pulmonary residual capacity, may increase the risk of hypoxemia and contribute to the increased severity. During the pandemic of 1918, maternal mortality was 27% (50% when influenza was complicated by pneumonia), and during the pandemic of 1957, 50% of deaths among reproductive-age women occurred among those who were pregnant. During the 2009 H1N1 influenza A pandemic, pregnant women were generally at increased risk for severe disease, including disease leading to hospitalization, admission to an intensive care unit, or death, as compared with nonpregnant women and the general population. In the United States, 5% of all deaths from pandemic influenza were among pregnant women, although pregnant women represent only about 1% of the U.S. population.
• What impacts the risk of malaria infection in pregnancy and what are the harmful effects?
In areas of high transmission, most women harboring parasites do not present with symptoms. Of pregnant women who are symptomatic, the majority are women having their first pregnancy; women who have been pregnant more than once and who live in areas where malaria is highly endemic are less likely to present with clinical signs or symptoms of malaria, even if they have high parasite loads. Pregnant women have a risk of severe malaria that is three times as high as that among nonpregnant women; a median maternal mortality of 39% has been reported in studies in the Asia-Pacific region. Maternal death also has been reported in association with P. vivax infection. The harmful effects of malaria (mainly due to P. falciparum) during pregnancy — maternal anemia, low birth weight, and preterm birth — have long been recognized. In areas of stable endemic transmission (e.g., sub-Saharan Africa), up to 25% of pregnant women have acute infection, leading to placental malaria. P. falciparum is the only species associated with placental sequestration, which is believed to be the cause of many of the manifestations of P. falciparum disease during pregnancy.
Morning Report Questions
Q: What is the impact of listeria infection during pregnancy?
A: Primarily a foodborne pathogen, listeria can contaminate a variety of raw foods, such as uncooked meats and vegetables, unpasteurized milk, and soft cheeses. Infection may be asymptomatic or may be manifested as an influenza-like illness; severe infection is rare during pregnancy, and no maternal deaths due to listeriosis have been reported among pregnant hospitalized women. L. monocytogenes infections most commonly occur during the third trimester and seem to be rare earlier in pregnancy. However, listeria has a predilection for the placenta and fetus, and, depending on the stage of pregnancy, listeriosis can lead to pregnancy loss, stillbirth, preterm birth, or serious neonatal disease.
Q: What changes in the immune system occur during pregnancy?
A: There is evidence that aspects of innate immunity (phagocytic activity, (alpha)-defensin expression, and numbers of neutrophils, monocytes, and dendritic cells) are maintained or enhanced during pregnancy, particularly during the second and third trimesters. Conversely, the number of CD3+ T lymphocytes (both CD4+ and CD8+) decrease during pregnancy as do Th1 and Th2 responses to mitogenic or antigenic lymphocyte stimulation. However, there is limited information on the longitudinal trends of such alterations during pregnancy. Levels of several cytokines are altered: levels of interferon-(gamma), monocyte chemoattractant protein 1, and eotaxin are decreased in most pregnant women, whereas tumor necrosis factor (alpha), interleukin-10, and granulocyte colony-stimulating factor levels rise. Data indicating that fetus-specific cytotoxic T-cell responses can be generated during pregnancy without loss of the fetus, as well as data from studies of pregnant mice showing normal memory T-cell development after lymphocytic choriomeningitis virus infection, contradict the idea of systemic immunosuppression during pregnancy. A more recent theory proposed a shift from Th1 to Th2 immunity during pregnancy. Th2 cells stimulate B lymphocytes, increase antibody production, and suppress the cytotoxic T-lymphocyte response, decreasing the robustness of cell-mediated immunity.