Abstract and Introduction
Abstract
A key component of the response to emerging infections is consideration of special populations, including pregnant women. Successful pregnancy depends on adaptation of the woman's immune system to tolerate a genetically foreign fetus. Although the immune system changes are not well understood, a shift from cell-mediated immunity toward humoral immunity is believed to occur. These immunologic changes may alter susceptibility to and severity of infectious diseases in pregnant women. For example, pregnancy may increase susceptibility to toxoplasmosis and listeriosis and may increase severity of illness and increase mortality rates from influenza and varicella. Compared with information about more conventional disease threats, information about emerging infectious diseases is quite limited. Pregnant women's altered response to infectious diseases should be considered when planning a response to emerging infectious disease threats.
Introduction
As strategies to deal with emerging infectious disease threats are developed, a key component is consideration of special populations, including pregnant women. Several issues are relevant to infectious disease threats during pregnancy. First, changes in immunity and physiology during pregnancy may make pregnant women more susceptible to or more severely affected by infectious diseases. Second, the effects of infectious diseases on the fetus may be unknown and difficult to predict, and diagnosis of infection in the fetus or infant can be challenging. Third, prophylaxis and treatment appropriate for the general population might not be appropriate for pregnant women. We focus on the first of these considerations: the immunology of pregnancy and the effects of emerging infectious diseases on the pregnant woman.
Although knowledge of the immunology of pregnancy has evolved tremendously over the past decade, many unanswered questions remain, such as how immune function is altered during pregnancy and how this alteration may affect susceptibility to and severity of infectious diseases. Although the effects of some infectious agents during pregnancy are well known, knowledge about many others is limited. A challenge to the study of infectious diseases during pregnancy is the selection of an appropriate control group; many studies have been retrospective and without control groups. Compared with knowledge about more conventional infectious disease threats, knowledge about novel and emerging infectious diseases during pregnancy is even more limited. Such lack of knowledge causes concern, given that an altered response to infectious diseases during pregnancy may require altered responses to emerging infectious disease threats. We describe the immunologic changes that may affect the course of infectious diseases in pregnant women, briefly summarize what is known about infectious diseases during pregnancy, and then focus on the particular challenges of dealing with emerging infectious diseases in pregnant women.