The World Health Organization has now declared that the Zika virus presents an emergency for the global health community. We still have a lot to learn about Zika before we know how to control transmission and how exactly it affects pregnancies. This outbreak brings to light an important component of pregnancy: immune suppression. A pregnant woman’s immune system downregulates so that her body doesn’t reject the growing fetus. However, this downregulation means that she and the developing fetus are more susceptible to viruses that we normally fight off without any side effects. Some of these viruses can be transmitted to the growing fetus and cause a congenital infection. In medical lingo, doctors often refer to these infections as the “TORCH” infections: Toxoplasmosis, Other (syphilis, parvovirus B19), Rubella, Cytomegalovirus (CMV), and Herpes viruses (like varicella zoster virus or VZV). In 2015, ACOG refreshed their Practice Bulletin on four of these infections: CMV, parvovirus B19, varicella zoster (VZV), and toxoplasmosis.
CMV is the most common congenital infection and occurs in up to 2% of infants. CMV is a universal virus that can infect anyone. For non-pregnant individuals, there are usually no symptoms but people can experience chills, fever, muscle soreness, fatigue, and changes in liver function. Once someone is infected, the virus hides out in cells and can become reactivated and cause a secondary infection in the future. If a pregnant woman contracts CMV or has reactivation of CMV, the virus can pass to the fetus through the placenta, during delivery, or breastfeeding. Most infants who contract congenital CMV have no symptoms whatsoever at birth. When symptoms appear, they can be quite severe: hearing loss, liver problems, deficiencies in blood cells, heart problems, growth restriction, and even death. CMV can lead to lifelong disabilities.
You may have seen this viral infection more than once if you spend any time with pre-school age children. It’s called “Fifth Disease” or sometimes Slapped Cheek Disease because of the rash it often causes. Unfortunately, the infected person is contagious before the rash appears and is no longer contagious by the time the visible signs of the virus appear. Up to 65% of pregnant women have been exposed to parvovirus B19 at some point in their lives. If a pregnant woman becomes acutely infected with parvovirus B19, there is a 17% to 33% chance that the fetus will contract the infection. Most fetal infections resolve without any problems, but parvovirus B19 can lead to miscarriage and stillbirth.
Varicella Zoster Virus (VZV)
The first time someone is infected with VZV they get chickenpox, a near universal experience in my generation, that has now largely been eradicated by the vaccine introduced in 1995. A person infected with chickenpox is contagious 48 hours before the rash appears until the vesicles crust over. Unfortunately, after causing the initial awful, itchy, blistery rash, the virus hides out in the nerves. If it reactivates, it causes a painful rash known as shingles. If a pregnant woman contracts VZV for the first time, the biggest risk is pneumonia. If the virus is transmitted across the placenta to the fetus, the fetus could become infected with chickenpox. Symptoms of such an infection are rare, but devastating: skin scarring, limb abnormalities, damage to the eyes, and a small skull. Fortunately, primary VZV infection in pregnancy is rare because many women have immunity from the having chickenpox in the past or having the VZV vaccine.
Toxoplasmosis is a parasite that lives inside cells. People become infected with the parasite if they eat the parasite, often associated with uncooked meat, contaminated foods, and cat feces. (Hence why pregnant women should not change cat litter!) Most people exposed will have no symptoms at all or mild swelling of the lymph nodes. In pregnant women, if the toxoplasmosis parasite enters the bloodstream, it can pass to the fetus through the placenta. Up to 90% of infected infants will eventually have symptoms of the infection: vision difficulties, hearing loss, and developmental delay.